Numerical simulation of dc-SQUID by FEM coupling with circuit equation taking into account phase difference of Josephson

junction

Naoya Terauchi, So Noguchi, and Hajime Igarashi

(Hokkaido University)

For development of high-performance superconducting quantum interference device (SQUID), it is desired to

analysis an electromagnetic phenomenon by numerical simulation. We have developed a simulation code of 3D

finite element method (FEM). In the previously developed code, the characteristics of superconducting thin film

and the macroscopic non-linear voltage-current property of Josephson junction were taken into account. However,

the non-linearity of voltage-current property is too strong to simulate the electromagnetic phenomenon accurately.

In this presentation, the quantization of magnetic flux is newly taken into account, and the SQUID is simulated

coupling the 3D FEM with electrical circuit equations. In the electrical circuit, phase difference at the Josephson

junction is also taken into account as microscopic phenomenon. Figure 1 shows a simulation result; the time

transition of the SQUID voltage obtained by the developed simulation code and the Runge-Kutta method. The

Runge-Kutta method is a conventional method. These two results do not agree well. The disagreement would be

caused by the difference of inductance in the two methods. In the FEM, the current path is time-varying in HTS

ring of finite width, therefore the actual inductance dependent on the current path is also varying. On the other hand,

in the Runge-Kutta method, the current path is assumed as a line current, so the inductance is constant and different

from that of the FEM. For development of a SQUD the macroscopic electromagnetic simulation taking into

account the accurate inductance value is imperative.

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 0.05 0.1 0.15 0.2

Vo

ltag

e (μ

V)

Time (μs)

Developed code

Runge-Kutta method

Figure 1. Time transition of SQUID voltage.

FDP-1

Quantum Interference in DC-SQUIDs Comprising Two Sub- Micron Aluminum Josephson Junctions:

Deviation from Classical Model

K. Miura*, K. Kikuchi, H. Shimada, Y. Mizugaki

(The University of Electro-Communications (UEC Tokyo))

In a small Josephson junction, the critical current IC is often found experimentally to be smaller than the value

IC0 expected by the Ambegaokar-Baratoff theory because of the effect of quantum phase fluctuations. It is empirically

known that IC decays from IC0 with decreasing the energy ratio between the Josephson coupling energy EJ and the

charging energy EC [1]. It is given by 21

C

J

2C0

C 2

1

E

E

I

I

. (1)

We also observed that quantum interference patterns of a dc-SQUID comprising sub-micron Al junctions deviated

from the classical model [2].

In this paper, we have compared the quantum interferences of three samples having different values of maximal

critical currents (Sample A~C). Figure 1(a) shows the equivalent circuit model of the dc-SQUID we used. The critical

current ICsq is modulated by applying a control current Icont directly to SQUID loop. Samples were fabricated using

e-beam lithography and shadow evaporation techniques. The maximal values of critical currents were varied by

changing oxidation conditions and deposition angles. Figure 1(b) shows optical and scanning electron micrographs

of Sample B. All the measurements were conducted in a compact dilution refrigerator at around 100 mK. In order to

compare the quantum interferences, the normalized critical current ICsq / ICsq0 are plotted in Fig.1 (c) as functions of

the effective energy ratio EJeff / EC. The effective Josephson coupling energy EJ

eff is given by

cont

0

Jsq0effJ ,

cos LIEE

, (2)

where EJsq0 is the Josephson coupling energy obtained by the Ambegaokar-Baratoff relation. In the classical model,

Icsq / ICsq0 is proportional to EJeff / EC, which means it has the slope of unity (two dashed lines) in Fig.1(c). The

experimental data of Sample A with the highest EJeff / EC tend to follow the classical model. On the other hand,

Samples B and C have steep slopes as compared to the classical model, which means that ICsq / ICsq0 decreases rapidly

with decreasing EJeff / EC. Our results indicate that quantum interference in the dc-SQUIDs is also influenced by

quantum phase fluctuations.

[1] M. Thinkham, Josephson effect in low-capacitance tunnel junction, in: H.Grabert, M.H. Devoret (Eds.),

Single Charge Tunneling, Plenum Press, New York, 1992, pp. 139-166.

[2] Y. Mizugaki et al. , Physica C 484 (2013) 206.

Figure 1. (a) Equivalent circuit of a fabricated dc-SQUID. (b) Optical and SEM images of Sample B.

(c) Dependence of normalized the critical current ICsq / ICsq0 on the effective energy ratio EJeff / EC.

(a) (b)

80 μm

500 nm

L / 2L / 2

–V

+V+Ib

–Ib

+Icont –Icont

(c)

0.001

0.01

0.1

1

1 10 100 1000

I Csq

/

IC

sq0

EJeff / EC

Sample ASample BSample Cslope of unity

FDP-2

Two-SQUID axial gradiometer using active magnetic shield

Akira Tsukamoto1,*, Tsunehiro Hato1, Seiji Adachi1, Yasuo Oshikubo1, Yusik Moon1, Masaki Sugisaki2, Masayuki Motoori2, Keiichi Tanabe1

(1ISTEC-SRL, 2JOGMEC) It is possible to find a metallic ore deposit by precisely measuring an anomalous distribution of the Earth’s magnetic field at the land surface (magnetic survey method). Since the Earth’s field changes by about several tens of nT (magnetic quiet day) or several hundreds of nT (geomagnetic storm) in a day, a gradiometer which can eliminate global changes of the magnetic field is suitable for use in the magnetic survey. In this study, we have developed an axial gradiometer consisting of two HTS-SQUIDs with a nonmagnetic cart for mobile measurement of dBz/dz. To keep feedback control during movement, an active shielding system using a fluxgate magnetometer was used. Figure 1 shows a photograph of the gradiometer system. The system including a cryostat covered with an aluminum RF shielding case, electronics such as FLL circuit, AD converter, wireless communication unit, Gyro sensor system, and battery was suspended from the ceiling of a frame. Therefore, the system attitude (vertical direction) was self-controlled by gravitational attraction. The baseline length was 0.3m. The active shielding system was evaluated by swinging motion with angular amplitude of 3 degree. Figure 2 shows the measured signals of two SQUID magnetometers (red and blue lines) and difference of them (black line) before and after applying the active shielding system. The field variation of 850 nTpp was reduced to 50 nTpp by using the active shielding system. The gradient signal obtained by difference of two magnetometer signals was 5 nTpp in real-time measurement as shown in a magnified graph. The gradient signal can be reduced to 1 nTpp (purple line) after adjustment of a subtraction parameter.

This work is a part of mineral exploration renovating program conducted by Japan Oil, Gas and Metals National Corporation (JOGMEC) and is fully funded by Ministry of Economy, Trade and Industry, Japan.

Figure 1. A photograph of the 2-SQUID gradiometer for mobile Figure 2. Effects of the active magnetic shield on the measured

measurement of dBz/dz of geomagnetism. signals during swinging.

FDP-3

Slit length dependence of rf-SQUID resonant frequency

Akira Sakai, Takuya Ashizuka, Yuji Miyato, Hideo Itozaki

Graduate School of Engineering Science, Osaka University

Superconducting quantum interference devices (SQUIDs) have been applied to wide variety

of magnetic sensing. Rf-SQUIDs must operate at high frequency, coupled with a readout coil. In

this study, Rf-SQUIDs were fabricated with YBa2Cu3Oy (YBCO) thin films deposited on SrTiO3

substrates. The resonant frequency formula for an rf-SQUID is,

f = 1

2π√LC

and depends on inductance L and capacitance C of the SQUID. Changing these parameters can

adjust resonant frequency. However, it is not clear to which part of the SQUID the L or C relates.

So we calculated the resonant frequency of the SQUID with an electromagnetic simulator. In

this calculation, superconductor was supposed to be perfect conductor, and dielectric constant of

an STO substrate was 2000. The SQUID model was set with the outer diameter of 3.5 mm, hole

size of 100×100 μm2, and slit width of 10 μm. The readout coil was positioned 0.5mm above the

SQUID. Electromagnetic field distribution was found to concentrate on SQUID slit at the

resonant frequency. It indicated that the SQUID slit should be strongly connected to the

resonant frequency. Therefore, SQUIDs with various slit length were designed for fabrication of

real device. For example, the SQUID design of slit length 5.1mm is shown in Fig.1. The

resonant frequency of SQUIDs decreased from 1200 MHz to 583.5 MHz, with increasing the

slit length ℓ from 1.465 mm to 5.1 mm[Fig.2]. Since the frequency decreasing trend was

proportional to 1/√ℓ, we concluded that L or C of the SQUID should partly come from the slit

length partly as shown in Fig.2.

Fig.2 The relation between slit length

and resonant frequency.

Fig.1 The SQUID dimensions. The length was

changed from 0.3 mm to 0.4 mm, and b

from 0.4 mm to 0.8 mm. Therefore, the

total slit length was changed from 3.1 mm

to 5.1mm.

a mm

b mm

3.5mm

FDP-4

5μm

10μm

100μm

10

0μ

m

Fig.1 The design of rf-SQUID.

00.20.40.60.8

11.21.41.61.8

2

0 1 2 3 4 5 6 7 8 9 1011

Res

onan

t fr

equen

cy[G

Hz]

Outer diameter [mm]

Fig.2 The relation between the outer diameter of the rf-SQUID

and (a) their resonant frequency and (b) effective area.

(a)design of the whole and

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 1 2 3 4 5 6 7 8 9 10 11

effe

ctiv

e ar

ea [

mm

2]

outer diameter [mm]

(b)center region of the rf-SQUID.

Resonant frequency dependence on outer diameter of high Tc rf-SQUID

Takuya Ashizuka, Akira Sakai, Yuji Miyato, Hideo Itozaki

Graduate School of Engineering Science, Osaka University

1-3 Machikaneyama, Toyonaka, Osaka 560-8531 Japan

E-mail: ashizuka@sup.ee.es.osaka-u.ac.jp

Superconducting quantum interference devices (SQUIDs) have been applied to wide variety of

magnetic sensing. An rf-SQUID can detect magnetic field signal by applying external rf-magnetic

field with its resonant frequency. The design of the rf-SQUID is important because it is related

with the resonant frequency and the effective area. In this study, we investigated its outer diameter

dependence of resonant frequency and effective area. The resonant frequency and the effective

area of the rf-SQUID was investigated by both electromagnetic field simulator and experiment.

In the experiments, we fabricated the rf-SQUID with YBa2Cu3Oy (YBCO) thin films deposited

on SrTiO3 substrates. The design of the SQUID were 5 types changing its outer diameter from 3.5

mm to 7 mm. We got the results of the resonant frequency for 5 types and the effective area for 3

types from 5 mm to 7 mm. The SQUID loop size, the slit width and Josephson junction width of

the SQUID were respectively 100 × 100 μm2, 10 μm and 5 μm (Fig.1). When increasing the

outer diameter of SQUID from 3.5 mm to 7 mm, the resonant frequency of SQUIDs was

decreased from 1108 MHz to 654 MHz. On the other hand, when increasing the outer diameter

of SQUID from 5 mm to 7 mm, the effective area of SQUID was increased from 0.30 mm2 to

0.39 mm2 (Fig.2). In the simulation, we built the SQUID model in electromagnetic field simulator.

The design of SQUID model were 9 types changing its outer diameter from 2 mm to 9 mm. We

investigated their resonant frequency and the effective area. It indicated that the operation

frequency and the effective area of the rf-SQUID should depend on the outer diameter of the

SQUID from both the electromagnetic field simulation and the experiment results.

Outer

Loop Slit

(a) (b)

diameter Simulation

Simulation

Experiment

Experiment (a)

(b)

FDP-5

Study of Ultra-Low Field SQUID-MRI System with a LC Resonator

M. Yamamoto*，H. Toyota，S. Kawagoe，J. Hatta，S. Tanaka

(Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi, Aichi 441-8580, Japan.)

We are developing an Ultra-Low Field (ULF) MRI system using HTS-rf-SQUID for food inspection. The

advantage of the ULF MRI system is that non-magnetic contaminants, which are difficult to be detected by a

magnetic sensor can be detected and localized. The system uses HTS-SQUID with a high sensitivity that is

independent of the frequency, because the signal frequency is reduced in the ULF. However the detection area of

HTS-SQUID is difficult to be increased. Therefore, we studied to increase the detection area using a LC resonator.

The LC resonator is composed of a coil (22.9 mH, Φ40 mm inner diameter) and a capacitor (setting resonance

frequency 1890 Hz). The signal is detected by a copper wound coil of the resonator, and transferred to HTS SQUID

which inductively coupled to the coil in liquid nitrogen.

The ULF MRI system is utilizing a pre-polarization magnet of 1.1 T, measurement field of 44.4 µT and gradient

field of 27.7 µT/m. The magnet was placed outside a magnetically shielded room. After a sample was pre-polarized

in the magnet, it was transferred from the magnet to measurement field and under the SQUID with the LC

resonator within 0.7 s. The pulse sequence is shown Figure 1. Radial scanning with spin echo technique was used.

We have studied reconstruction of 2D-FFT method using a gridding method in addition to a filtered back projection

method.

In this research, we combined the LC resonator with an ULF MRI system, and obtained the 2D-MRIs. As a result,

the signal detector, which consists of the SQUID and the LC resonator, provided a 1.5 times larger detection area.

Figure 1. Pulse sequence for 2D-MRI

Gｙ

Bp

LC resonator

Measurement

Signal

624 ms

5 sor more

Main trigger

BAC

Bm

512 ms

0.53 ms

Transfer time

1.06 ms

500 ms 500 ms

256 ms 256 ms

694 ms

Gｚ

FDP-6

Development of Non-Destructive Evaluation System Using an HTS-SQUID Gradiometer with an External Pickup Coil

J. Kawano*,1, S. Kawauchi1, F. Ishikawa1, K. Tanabe2

(1The Chugoku Electric Power Co., Inc., 2ISTEC-SRL) We investigated the possibilities of non-destructive evaluation (NDE) system using an HTS SQUID gradiometer for the purpose of detecting defects in a real field such as a power plant. In order to detect defects in magnetic or magnetized conductors used as a practical material, correct operation of SQUID sensor in a relatively high static magnetic field is required. Moreover, a flexible sensor or sensor probe is needed to detect defects in a real field. An external pickup coil method is one of the solutions of these requirements. In the past research, we could observe defect-induced magnetic signals without appreciable influence of static magnetic field by employing the external pickup coil method. (In this case, the pickup coil was fixed and cooled by LN2 in a cryostat.)

In the present research, we have fabricated a flexible sensor using a normal conducting Cu pickup coil, and have investigated its performance. The Cu coil, as an external pickup coil, was connected using a Cu wire to the input coil of the SQUID. The SQUID was fixed and cooled by LN2 in a cryostat, while the pickup coil was set outside of the cryostat. The characteristics of the SQUID sensor connected with the Cu pickup coil vary with varying the pickup coil parameters such as the diameter of the Cu wire and the number of turns. In the present study, we fabricated 4 pairs of Cu pickup coils with the diameter of Cu wire of 0.4mm, 0.5mm, the number of turn of 28, 32, 56, the size of pickup coil of 35mm, 45mm. Measured results showed that the number of turn and the size of pickup coil had relatively small influence on the sensitivity of the SQUID sensor with the external pickup coil, and suggested that the performance of the present SQUID sensor is mostly determined by the resistivity of the Cu coil.

FDP-7

Magnetic coupling between SQUID and Probe

of STM-SQUID Microscope

Kouhei Hisayama*, Yasunori Matsui, Yuji Miyato, and Hideo Itozaki

(Graduate School of Engineering Science, Osaka University)

We have developed an STM-SQUID microscope by combining a scanning tunneling microscope (STM) and a

high-Tc superconducting quantum interference device (SQUID) to observe the surface morphology and magnetic

field. In our microscope, a permalloy probe (the diameter: 90 µm) with high permeability, whose tip was

electrochemically polished, was placed between the SQUID and the sample. The probe played the role of a flux

guide to transfer the local magnetic field of the sample to the SQUID. The probe tip could be approached as close

as possible to the sample surface within a few nm by an STM feedback control with the tunneling current from the

sample to the probe. We have investigated on magnetic coupling between the SQUID and the probe. They were

separated from 4.5 mm to 0.1 mm. We used a Ni thin film as a sample. Magnetic signal that detected by SQUID

increased as distance between the SQUID and the probe decreased (Fig 1). When the distance was 3 mm, amplitude

of SQUID signal was about 0.5 mV (Fig 2(a)), and when the distance was decreased 0.1 mm, amplitude became 5.8

mV (Fig 2(b)). On each experiment, we used the same SQUID, probe and sample. The obtained magnetic image

became clear as distance between the SQUID and the probe decreased (Fig 2). Therefore the end point of the probe

should be closed to the SQUID hole as possible as it could be. It makes clearer magnetic image.

(a) (b)

Figure1. SQUID output and distance between SQUID Figure2. Sample surface magnetic image.

probe. Sample is Ni thin film.

Distance between SQUID and probe are 3

mm (a) or 0.1 mm ( b).

Distance between the

SQUID and the probe [mm]

SQ

UID

ou

tpu

t [m

V]

500nm

SQ

UID

ou

tpu

t [m

V]

3

Distance [μm] 2.3 Distance [μm]

500nm

-4 2.3

2

0

2

4

6

8

0 2 4 6

SQ

UID

ou

tpu

t a

mp

litu

de

[mV

]

-3

FDP-8

Microstructure Observation of CaFe2As2 Family Thin Films by Transmission Electron Microscopy

T. Kawaguchi*,1, S. Harada2, R. Fujimoto3, Y. Mori3, I. Nakamura3, T. Hatano3, T. Ujihara2,

H. Ikuta3

(1VBL, Nagoya Univ., 2Dept. Materials Science and Engineering, Nagoya Univ., 3Dpt.

Crystalline Materials Science, Nagoya Univ.)

For single crystals of CaFe2(As1xPx)2 (P-Ca122), superconductivity was observed in a small range of 0.03 x

0.05, with the highest transition temperature (Tc) of 15 K [1]. The samples with larger phosphorous contents

underwent a structural transition to the “collapsed tetragonal” phase and superconductivity was suppressed [1]. On

the other hand, epitaxial thin films of P-Ca122, which were successfully grown on (La,Sr)(Al,Ta)O3 (LSAT)

substrates by molecular beam epitaxy (MBE) recently, showed a superconducting transition up to higher phosphorous

contents [2]. In addition, the x=0.14 thin film had a Tc of 21.4 K that is higher than the maximum value of the bulk

samples. In this report, we investigated in detail the microstructure of the P-Ca122 thin films by transmission electron

microscopy (TEM) and scanning transmission electron microscopy (STEM).

P-Ca122 thin films were grown on LSAT(100) and MgO(100) substrates with substrate temperatures of 650-700oC

and a growth rate of 100 nm/h by MBE. The elements were supplied by heating solid sources of Ca, Fe, As and GaP.

The composition of the thin films was adjusted using data of a flux monitor mounted in the growth chamber and an

ex-situ analysis by an electron probe micro-analyzer (EPMA).

First, we investigated the element distribution of a thin film with x=0 grown on a LSAT substrate by energy

distribution x-ray spectroscopy (EDS) elemental mapping equipped in STEM. The composition of the thin film was

homogeneous and defects were hardly observed. Furthermore, the atomic arrangement of the layered structure of

CaFe2As2 was clearly resolved by STEM. These observations indicate that the thin film has a good crystalline quality.

A thin Ca-O layer (2-3 nm), however, formed at the interface between the thin film and LSAT. A similar Ca-O layer

was also observed in the P-doped thin film. These results indicate that P-Ca122 reacts with LSAT substrates during

the growth. Such a Ca-O layer was not observed for an x=0 thin film grown on MgO, indicating that CaFe2As2 does

not react with MgO. On the other hand, the thin film on MgO had many domains that are 45o-rotated to each other

about the c-axis lattice direction, and stacking faults of (100) plane were observed. This is probably due to the large

lattice mismatch between CaFe2As2 and MgO.

[1] S. Kasahara et al., Phys. Rev. B 83, 060505 (2011).

[2] T. Hatano et al., submitted to ISS2014

FDP-9

MBE growth of superconducting NdFeAs(O,F) thin film without a fluoride top layer

M. Chihara

*, N. Sumiya, K. Arai, T. Hatano, H. Ikuta

(Department of Crystalline Materials Science, Nagoya University)

Among the various iron-based superconductors discovered to date, LnFeAs(O,F) (Ln: lanthanoid) has the highest

critical temperature (Tc) that is a great advantage for applications. We have realized the growth of superconducting

NdFeAs(O,F) thin films by molecular beam epitaxy (MBE) [1]. In these earlier studies, fluorine was doped from a

NdOF top layer that was formed on the mother compound, NdFeAsO. Although, superconducting thin films with

Tc as high as bulk samples can be obtained by this method, it has a disadvantage for some applications such as

planar superconducting junctions, because the surface is covered with NdOF. Therefore, superconducting thin films

without having such a top layer is highly desired. Recently, a one-step growth of SmFeAs(O,F) by using FeF2 as F

source was reported [2]. Here, we report another method that realized such a one-step growth of NdFeAs(O,F).

NdF3, Fe, As, Ga, and O2-gas were used as the source materials. NdF3 supplies both Nd and F, in excess of F. The

excess F was removed by Ga, which works as a F-getter [3]. The most crucial improvement from our previous

studies was the elimination of undesirable gas. It turned out that an unignorable amount of N2 gas existed in the

chamber, detected by QMS (Quadrupole Mass Spectrometer). This stemmed from the PBN (Pyrolitic Boron

Nitride) crucible used for the Fe source, probably through a reaction between the crucible and the source element.

By changing the PBN to an alumina crucible, the amount of N2 was greatly suppressed. Thereafter, we adjusted

carefully the supply of oxygen and Ga, and have grown several thin films. Figure 1 shows such a NdFeAs(O,F)

thin film that was single phase. The c-axis length was 0.8578 nm, indicating that fluorine was doped although no

NdOF layer was grown on top to the thin film. Figure 2 shows the temperature dependence of resistivity for the

same thin film, and indeed we observed a clear superconducting transition with an onset Tc of 50 K. We think that

N2 had hindered the growth of NdFeAs(O,F), and increasing the migration of the raw materials was crucially

important to realize the one-step growth of superconducting NdFeAs(O,F).

[1] T. Kawaguchi et al., Appl. Phys. Lett. 97, 042509 (2010). [2] M. Naito et al., ISS2013 FD-2. [3] T. Kawaguchi

et al., Appl. Phys. Express 4, 083102 (2011)

Fig. 1. XRD pattern of an as-grown NdFeAs(O,F) thin film. Fig. 2. Temperature dependence of

resistivity of the thin film of Fig. 1.

0 10 20 30 40 50 60 70 80100

101

102

103

104

105

001

003 004

005 006

007

Inte

nsi

ty (

cps)

002

2 (degree)

MgO

NdFeAs(O,F)/MgO

0 100 200 3000

0.2

0.4

0.6

Temperature (K)

Res

isti

vit

y (

m

cm)

Tc=50 K

NdFeAs(O,F)/MgO

FDP-10

One-step Growth of SmFeAs(O,F) Films by Molecular Beam Epitaxy

Takanobu Tsuneki*,1

, Hiroaki Sugawara1, Masahito Sakoda

1, Daiki Watanabe

1,

Akiyasu Yamamoto2, and Michio Naito

1

(1Department of Applied Physics, Tokyo University of Agriculture and Technology,

2Department of Applied Chemistry, University of Tokyo)

The iron-based superconductor, SmFeAs(O,F), has the highest Tc of 56 K and is the most attractive in potential

applications for superconducting devices. In the previous article [1], we reported on our growth of superconducting

SmFeAs(O,F) films by post-growth F diffusion. The F diffusion approach provides films with excellent

superconducting properties but has a problem of the existence of an undesired layer of SmOF and/or SmF3 on the

surface of films. This is a serious problem for multilayer deposition required for fabricating sandwich-type Josephson

junctions. To avoid this problem, we have been developing one-step growth of superconducting 1111 films without

post-growth F diffusion. The key issue for one-step growth is a fluorine source. The assist by molecular F2 or HF gas

is not realistic. A few candidates have been proposed as a solid fluorine source. Atomic F from FeF3 accompanied with

the decomposition of FeF3 FeF2 + F was proposed by Nagoya group, but we found that FeF3, even if so-called

“anhydrous”, is hydroscopic and contains a substantial amount of water, which is an obstacle to reproducible growth.

Our previous attempt to use SmF3 also encountered poor reproducibility [2]. The reason is that SmF3 is too stable to

decompose at the substrate temperature as low as 650C, suggesting that “softer” (= easier to decompose) fluorides

are preferable as a fluorine source. In this presentation, we report that FeF2 is a promising candidate as a fluorine

source.

In the growth of the films, we codeposited Sm, Fe, FeF2 and As in oxygen atmosphere in an UHV chamber. FeF2 was

deposited from FeF2 pellets using resistive heating. The deposition for 10 min produced 850 Å thick films of

SmFeAs(O,F). We have found that with FeF2 as a fluorine source, the growth window to obtain phase-pure

SmFeAs(O,F) is much wider than with SmF3. The highest Tcon

(Tcon

) is 56.0 K (54.0 K) on CaF2. Figure1 shows M-H

hysteresis and Jc-B of one SmFeAs(O,F) film grown on CaF2. The Jc of the film is high, 2.4 MA/cm2 at 5 K, under

self-field.

[1] S. Ueda et al., Appl. Phys. Letters 99, 232505 (2011).

[2] S. Ueda et al, Appl. Phys. Express 5 053101(2012).

Figure1 (a) M-H hysteresis curve and (b) Jc-B of SmFeAs(O,F) films grown on CaF2(001).

FDP-11

FeSe0.5Te0.5 thin films grown on CaF2 substrate

by pulsed laser deposition

Pusheng Yuan, Zhongtang Xu, Qi Liu and Yanwei Ma

Key Laboratory of Applied Superconductivity, Institute of Electrical Engineering, Chinese

Academy of Sciences, PO Box 2703, Beijing 100190, China

Abstract

Superconducting epitaxial FeSe0.5Te0.5 thin films on CaF2 (001) substrate were prepared

by pulsed laser deposition. By varying the deposition temperature (250-350 oC) and thickness

(30-130 nm) high purity phase and fully epitaxial films are obtained. It is found that the c-axis

lattice, determined by both the film thickness and the deposition temperature, is linearly

related to the superconducting transition temperature (Tc). When c-axis constant reaches a

minimum, the best films are obtained. These films showed Tconset

= 20 K and Tc0= 18.8 K, Jc of

these films at T= 4.2 K was 0.5×106Acm

2 in self-field and 0.2×10

6 Acm

2 at 7 T,

respectively.

FDP-12

Effects of Co-Doping on Cl-doped Y123 Thin Films Prepared by Fluorine-Free MOD Method

Takanori Motoki*,1, Jun-ichi Shimoyama1, Akiyasu Yamamoto1, Hiraku Ogino1,

Kohji Kishio1, Genki Honda2 and Tatsuoki Nagaishi2

(1University of Tokyo, 2 Sumitomo Electric Industries, Ltd.)

The fluorine-free metal organic decomposition (FF-MOD) method has been developed as one of the promising

method to prepare RE123 (RE:rare earth elements) thin films because of the very fast crystallization (less than a few

minutes) [1] and high homogeneity. However, FF-MOD processed RE123 films show lower Jc than films prepared

by other methods, such as PLD, MOCVD and TFA-MOD, especially in magnetic fields. Our preliminary study

revealed that doping of Cl to starting solution resulted in generation of oxychloride Ba2Cu3O4Cl2 (Ba2342) crystals.

Detailed analysis on microstructure indicates that c-axis aligned Ba2342 crystals were generated in the Y123 film

and coherently connected with SrTiO3 and/or Y123 due to good lattice matching, which supported c-axis alignment

of Y123 and improved in-field Jc. It is empirically known that Jc of RE123 films decreases as an increase of the

film thickness. However, our Cl-doped Y123 films kept high Jc at 40 K up to a thickness of ~0.93 m reflecting

their high crystallinity.

In the present study, we studied co-doping effects on crystallinity, microstructure and critical current properties of

Cl-doped Y123 films. Dilute co-doping of Sn, Zr or Hf was found to be effective for enhancement of in-field Jc of

Y123 films, while degradation of c-axis alignment always occurred in the metal doped and Cl-free Y123 films.

Especially, co-doping of Cl and 1 mol% Hf largely improved Jc higher than 1 MA cm-2 at 40 K under ~5 T. Very

fine oxide precipitates with several nm in size were observed in its cross-sectional images, which were considered to

contribute to improved flux pinning properties.

[1] Y. Ishiwata et al., IEEE Trans. Appl. Supercond. 23 (2013) 7500804.

FDP-13

Optimization of the Fluorine in Solution for GdBCO Film Growth

L.H. Jin*,1, C.S. Li1, Z.M. Yu1, J.Q. Feng1, S.N. Zhang1,

A. Sulpice2, Y. Wang1, P.X. Zhang1

(1Northwest Institute for Nonferrous Metal Research, Xi’an 710016, P. R. China, 2Institut Néel and CRETA, CNRS&UJF, 25 avenue des Martyrs, BP 166, F-38042

Grenoble Cedex 09, France)

The low fluorine solution was useful for the decrease of the amount of corrosive fluorine-containing gas and the fast pyrolysis process. In this study, the low fluorine solutions containing different content of fluorine were prepared. The low fluorine solutions had 7.7%-23% of fluorine content in the traditional all TFA solution, which were useful for the epitaxial growth of GdBa2Cu3Oy (GdBCO) film. GdBCO films were deposited on RABiTS substrates by chemical solution deposition process using these low fluorine solutions. The phase formation, texture, microstructure and superconducting properties of GdBCO films were characterized by x-ray diffraction, scanning electron microscopy and four-probe method. The composition of precursor films was optimized to control the formation of BaF2 and to reduce the formation of BaCO3. With increasing of fluorine, the traces of intermediate phase (Ba1-xGdxF2+x) were observed. The GdBCO films with a critical current density (Jc) of ~ 2 MA/cm2 (77 K) could be obtained by using these low fluorine solutions.

FDP-14

Preparation of Non-c-axis Oriented BSCCO Thin Films by the MOD Method

Y. Yamada＊,1, N. Mori1, T. Atsumi1, T. Ishibashi2

(1 National Institute of Technology, Oyama College, 2 Nagaoka University of Technology)

1. Introduction

The oscillator using intrinsic Josephson junctions of BSCCO is considered to be a promising device that fills

the frequency domain called the "terahertz gap". It has already been proved that the W class continuous coherent

terahertz wave can be oscillated [1]. The major preparation methods thus far reported on the BSCCO intrinsic

Josephson junction device require complicated procedures, such as the etching process of c-axis oriented BSCCO

thin films in the depth direction. However, if non-c-axis oriented thin films are used, it would be possible to prepare

the planar type device without the etching in the depth direction.

The metal organic decomposition (MOD) method is attractive as one of the useful preparation techniques for

large-size films. High quality c-axis oriented BSCCO thin films have been prepared by this method [2, 3], and also

the crystal orientation is controllable by selecting a suitable substrate. In this study, we report on the preparation of

MOD BSCCO thin films with the non-c-axis orientation using NdGaO3 (NGO) (100) and SrTiO3 (STO) (110)

substrates.

2. Experimental

BSCCO thin films were prepared by the MOD method using a BSCCO metal organic (MO) solution purchased

from Kojundo Chemical Lab. Co., Ltd.. Preparation procedures are as follows:

(1) 6 BSCCO MO solution was dropped onto substrates using a digital micropipette.

(2) The dropped solution was spincoated by 2-step process using 500 rpm for 5 sec and 3000 rpm for 1 min.

(3) The spincoated films were dried in a thermostat chamber at 120ºC for 40 min.

(4) The films were annealed at a fixed temperature between 640ºC and 810ºC for 2 h in O2 atmosphere.

The crystal structures of the annealed BSCCO thin films were investigated by X-ray diffraction (XRD)

measurements. The resistive transition curves were measured using a cryostat.

3. Results

Figure 1 shows XRD patterns of the film grown on NGO(100) substrate at 640ºC. The (115) diffraction peak of

Bi2201 is observed at 2 = 29.8º. This result indicates that the Bi2201 c-axis inclines approximately 52 degrees

to the normal incidence. The same peak appears in all samples prepared at 640 and 690 on the NGO(100)

and STO(110) substrates. The details of XRD results are reported together with those of other experiments.

Acknowledgements

This study was partly supported by Grant-in-Aid for

Cooperative Education and Research among Nagaoka University

of Technology and National Colleges of Technology.

References

[1] L. Ozyuzer et al., Science 318, 1291 (2007)

[2] H. Iwasaki et al., IEEE Trans. Appl. Supercond., 15, 3058 (2005)

[3] Y. Deguchi et al., Physics Procedia 45, 193 (2013)

Figure 1 X-ray diffraction patterns for 640ºC sample.

2 (degree)

Inte

nsi

ty (

a.u

.)

Bi2

20

1(1

15

)

NG

O(2

00

)

FDP-15

Thermal Imaging of Bi2212 THz Oscillator

H. Akiyama

1*, S. Pyon

1, T. Tamegai

1, M. Tsujimoto

2, I. Kakeya

2

(1Department of Applied Physics, The University of Tokyo,

2Department of Electric Science & Engineering, Kyoto University)

It was discovered that Bi2Sr2CaCu2O8+ (Bi2212) mesas generate THz radiation in a particular configuration [1].

Bi2212 mesas are promising for THz generator, which can fill the frequency range around “THz gap”. On the other

hand, it is known that Bi2212 mesas show self-heating effects (hot spots) when the current is passed to Bi2212

mesas due to the low thermal conductivity along the c-axis. While some studies reported that the hot spot promotes

the coherent THz emission from Bi2212 mesas [2], other studies showed that it is unrelated to THz emission [3].

Further investigations on the relation between the hot spot and THz emission from Bi2212 mesas are necessary.

In order to address this issue, imaging of temperature distribution on Bi2212 mesas is expected to be effective.

We obtained the surface temperature distribution of the sample by fluorescent thermal imaging (FTI) method [4]. It

is based on the strong temperature dependence of fluorescence intensity of organic fluorescent material “EuTFC”.

Figure 1 shows the temperature dependence of the fluorescence intensity of EuTFC. It clearly demonstrates that

this technique has an excellent temperature resolution in a broad temperature range below 100 K. Figure 2 shows a

thermal image of the meander lines of manganin wire heated by the current flow. It demonstrates that this technique

has also a sufficient spatial resolution (~2 m) for thermal imaging of Bi2212 mesas. In this work, we obtain the

thermal images of Bi2212 mesas with high spatial resolution and investigate the relation between temperature

distribution and I-V characteristics.

[1] L. Ozyuzer et al., Science 318, 1291 (2007).

[2] H. Wang et al., Phys. Rev. Lett. 105, 057002 (2010).

[3] H. Minami et al., Phys. Rev. B 89, 054503 (2014).

[4] P. Kolodner et al., Appl. Phys. Lett. 40, 782 (1982).

Fig. 1 Temperature dependence of the

fluorescence intensity of EuTFC.

Fig. 2 (a) An optical image of meander lines of manganin wire

(white regions). (b) Thermal imaging of the same region when

the current is passed through the wire.

FDP-16

YBCO nanoscale structures in Hybrid devices

Reza Baghdadia, Riccardo Arpaiaa, Thilo Baucha, and Floriana Lombardia

aQuantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers

University of Technology

Abstract

The advances of nanotechnologies applied to High Temperature Superconductors (HTS) opennew perspective in the realization of hybrid devices, where HTS materials are interfaced withTopological Insulator (TI) or graphene. In particular the much higher values of the superconduc-tive gap and of the critical magnetic field of HTS with respect to conventional superconductorscould make experiments aiming at the detection of Majorana fermions more accessible [1].There are many challenges to pattern Y Ba2Cu3O7 − x (YBCO) nanostructures, so limiting thestudy of hybrid devices with YBCO electrodes. Oxygen out-diffusion, often observed during theresist baking and ion beam milling, is the major limiting factor in patterning YBCO thin films.This issue becomes more severe when several e-beam (EBL) steps are required. Here we presenta novel fabrication technique that allows obtaining YBCO nanogaps below 50nm. This hasbeen achieved by protecting the sides of the electrodes with a Pt/Au bilayer during subsequentEBL steps and by using a low temperature resist baking. The effective width of the nanogapis depended on the damage the electrodes undergo during the patterning. To assess it, we havestudied YBCO nanowires with different widths (60 − 600nm) and lengths (1 − 50µm). Thenanowires with the top and the sides protected by Pt/Au bilayer have been characterized byResistance-Temperature R(T) and by current-voltage measurements.For comparison we have also fabricated nanowires where the sides were not covered by Pt/Auand that were intentionally covered and baked with resist. In the first case by analyzing theR(T) transitions of 1µm long wires with the Little model [2], we have found a good fitting forwidths down to 60nm, by considering a dead layer of ≈ 20 nm on both sides of the wire. Insteadnanowires fabricated without protecting Pt/Au did not show any superconducting transition forwidth below 400nm. This confirms the validity of our approach and gives an upper value of80 − 100nm for our narrowest effective nanogap width.Au film has been used to bridge the YBCO nanogaps. The structures have been subsequentlypatterned to obtain SNS junctions. For the narrowest nanogaps we have observed a proximityeffect with supercurrent densities as high as 5×105A/cm2 at T = 4K. The Josephson nature ofthe supercurrent has been confirmed by the detection of Shapiro steps in microwave field and bymagnetic field oscillation of the supercurrent, approaching an almost Fraunhofer-like dependenceclose to the critical temperature of the junctions (80K). The observation of a proximity effectthrough the Au layer clearly demonstrates the feasibility of our YBCO nanogaps procedure tofabricate hybrid devices where the normal Au barrier could be replaced by Graphene, TI, semi-conducting nanowires. The work is in progress.

References1- P. Lucignano et. al, Phys. Rev. B, 86, 144516 (2012)2- A. Bezryadin, J.Phys.Cond.Mat., 20, 043202 (2008)

1

FDP-17

Numerical Investigation on Defects Identification in HTS Film

by Contactless Methods

Teruou Takayama*,1, Atsushi Kamitani1

(1Yamagata University) Claassen et al. have proposed the inductive method for contactlessly measuring a critical current density jC of high-­temperature superconductors (HTSs). They monitored a harmonic voltage induced in a coil by applying an ac current to the coil placed just above an HTS film. It is found that, only when a coil current exceeds a threshold current, the third-­harmonic voltage develops suddenly. Consequently, jC can be evaluated from the threshold current. In contrast, Ohshima et al. have proposed a standard permanent magnet method. In the method, while moving a permanent magnet above an HTS film, electromagnetic force Fz acting on the film is measured. They found that the maximum repulsive force FM is roughly proportional to jC. This means that jC can be evaluated from the measured value of FM. Although two types of the contactless method described above have been also applied to the crack detection by measuring jC-­distributions in an HTS sample, they become time-­consuming due to the measurement of jC at each measurement point. Hattori et al. have recently proposed the scanning permanent magnet method to improve the speed of the jC-­measurement. In the method, the magnet is placed in relation to a film surface at a constant distance between an HTS surface and the magnet bottom, and it is moved in the direction parallel to the surface. As a result, they found that a jC-­distribution can be obtained from a measured Fz-­distribution, and the measurement speed of the scanning method is higher than the standard one. Note that this method has been not yet applied to the crack detection. The purpose of the present study is to numerically investigate the resolution of the inductive/scanning permanent magnet methods for identifying multiple defects. To this end, we develop a numerical code for analyzing the time evolution of the shielding current density in an HTS film containing the defects.

FDP-18

Rough Surface Effect on a Broken Time-Reversal Pairing State in d-Wave Superconducting Films

Seiji Higashitani*, Nobumi Miyawaki(Graduate School of Integrated Arts and Sciences, Hiroshima University)

It is well known that unconventional superconducting states in thin films are quite different from the corresponding bulk states. Quasiparticle scattering at the film surfaces gives rise to substantial pair breaking and simultaneously yields surface Andreev bound states. Recently, Vorontsov discussed a possibility of a broken time-reversal state in d-wave superconducting films [1]. This state is characterized by a gap function oscillating along the film surface and generates a spontaneous current. The current near the surface, which is carried by the surface Andreev bound states [2], flows in the opposite direction to that in the middle region of the film; the total current vanishes and hence the broken time-reversal state can be the ground state of the film. Vorontsov found that such a state is realized in a wide range of the film thickness. In his theory, however, the surfaces of the film are assumed to be specular. Actual films cannot be free from atomic-scale surface roughness, which is sufficient to scatter quasiparticles at the Fermi level diffusively. The diffusive surface scattering is known to modify significantly the spatial profile of the self-consistent d-wave gap function and the surface density of states [3]. In this work, we address the effect of surface roughness on the critical thickness below which the broken time-reversal d-wave state becomes unstable. We report numerical results for the temperature dependence of the critical thickness.

[1] A. B. Vorontsov, Phys. Rev. Lett. 102, 177001 (2009).

[2] S. Higashitani, J. Phys. Soc. Jpn. 66, 2556 (1997).

[3] K. Yamada, Y. Nagato, S. Higashitani, and K. Nagai, J. Phys. Soc. Jpn. 65, 1540 (1996).

FDP-19

Layer Number Dependence of Flux Avalanches in Superconducting Shifted Strip Array

A. Mine*, 1, Y. Tsuchiya1, S. Miyano1, S. Pyon1, T. Tamegai1, S. Nagasawa2,

M. Hidaka2

(1Dept. of Appl. Phys., The Univ. of Tokyo, 2AIST)

In recent years, superconducting meta-materials are attracting great attention as one of the applications of

nano-structured superconductors. For example, magnetic cloaking can be realized by using nano-structured

superconductors with anisotropic magnetic permeability and ferromagnetic materials [1]. A superconducting strip

array has a large anisotropy in the magnetic permeability [2]. However, flux avalanches due to thermo-magnetic

instabilities can occur easily, since a strip array also has a large demagnetization factor which destroys the magnetic

cloaking. We have fabricated Nb superconducting shifted strip arrays (SSAs) with 2 and 3 layers, and observed flux

penetration by using a magneto-optical imaging (MOI) method [3]. We found that flux avalanches of various forms

occur depending on temperature, the value of w/a (strip width: w, lattice constant: a) and the number of layers.

In order to clarify how the condition for the flux avalanche changes with the number of layers of strips, we have

fabricated SSAs with up to 4 layers (Fig. 1) and observed flux penetration processes by using an MOI method.

With the overlap ratio w/a = 0.75, flux avalanches are spot-like in a 2-layer SSA (Fig. 2(a)), while in a 3-layer SSA

additional flux penetrations along the strips are observed (Fig. 2(b)). We find that linear avalanches perpendicular

to the strip occur in a 4-layer SSA (Fig. 2 (c)) in addition to the flux penetrations along the strips. At this overlap

ratio, linear avalanches occur only in a 4-layer SSA. We will discuss temperature and w/a dependence of flux

avalanches forms and the threshold field, where the avalanche occurs first, in 4-layer SSAs comparing them with

those in the 2- and 3-layer SSAs.

[1] J. B. Pendry et al., Science 312, 1780 (2006).

[2] Y. Mawatari et al., Phys. Rev. B 85, 134524 (2012).

[3] Y. Tsuchiya et al., Supercond. Sci. Technol. 26, 095004 (2013).

Fig. 1 Schematic drawing of a 4-layer SSA. w and a are the width and the lattice constant of the strips, respectively.

Fig. 2 Magneto-optical images of flux avalanches in SSAs (w = 20 m, w/a = 0.75) with (a) 2 layers, (b) 3 layers,

and (c) 4 layers at 5.0 K.

FDP-20

A HTS DUAL-BAND BANDPASS FILTER USING STUB-LOADED HAIR-PIN RESONATORS WITH

INDEPENDENTLY CONTROLLABLE BANDWIDTHS

S. Sugiyama

*, N. Sekiya

(University of Yamanashi)

We have developed a high-temperature superconducting (HTS) dual-band bandpass filter (BPF) using

stub-loaded hair-pin resonators with independently controllable bandwidths. The proposed dual-band BPF is

composed of five stub-loaded hair-pin resonators with H-shaped waveguides between them. The resonator has

even-mode and odd-mode. The resonator enables independent control of the even-mode and odd-mode resonant

frequencies [1]. The main advantage of the proposed filter was to enable independent control of the bandwidths of

the even- and odd- modes. The coupling coefficient of the even-mode was controlled by the distance between the

resonators, which did not affect the coupling coefficient of the odd-mode. On the other hand, the coupling

coefficient of the odd-mode was controlled by the H-shaped waveguide, which did not affect the coupling

coefficient of the even-mode.

An electromagnetic simulator was used to design and analyze the filter, which had a 3.5-GHz center frequency

and a 70-MHz (2%) bandwidth for the first band (odd-mode) and a 5.0-GHz center frequency and a 250-MHz (5%)

bandwidth for the second band (even-mode). The filter was fabricated using double-sided YBa2Cu3O7 thin film on

a 25×25×1.0 mm Al2O3 substrate. The simulated and measured frequency responses of the dual-band BPF are

shown in Fig.1. The measured results agree well with the simulated one.

[1] N. Sekiya, S. Sugiyama, “HTS dual-band bandpass filters using stub-loaded hair-pin resonators for mobile

communication systems”, Pysica C, (2014), to be published.

Acknowledgements:

The authors would like to thank the Japan Steel Works, Ltd for providing YBa2Cu3O7 thin film.

Figure 1. Simulated and measured frequency responses of the proposed HTS dual-band BPF.

-100

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0

3 3.5 4 4.5 5 5.5 6

Sim_S21Mea_S21

S2

1 [d

B]

Frequency [GHz]

FDP-21

DESIGN OF HTS MICROSTRIP-LINE DUAL-BAND

BANDPASS FILTERS USING CROSS-COUPLED RESONATORS FOR HIGH POWER APPLICATION

K.Fujihara, N.Sekiya

(University of Yamanashi)

We have designed a high-temperature superconducting microstrip-line dual-band bandpass filters (DBPFs) using

cross-coupled resonators for high power application. The dual-band response is realized by placing attenuation pole

within the bandwidth of a wideband filter. An electromagnetic simulator based on the moment method was used to

design and analyze the filter. A center frequency of the wideband approach is 5 GHz, and 1.0 % bandwidth in each

pass-band is to be retained after placing attenuation pole at 4.98 GHz and 5.02 GHz. We assumed Al2O3 was used

for the substrate and that the substrate had a dielectric constant of 9.9 and a thickness of 0.5 mm. To investigate

current distribution of the DBPF, the maximum current density of the each resonator was simulated. Figure 1 shows

the simulated frequency responses of the proposed DBPF. The simulated frequency responses of the DBPF were in

a reasonable agreement with the design parameters. The details of the measured frequency responses and power-

handling capability will be reported at the symposium.

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-40

-30

-20

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0

4.6 4.8 5 5.2 5.4

S11S21

S11,S

21 [

dB

]

Frequency [GHz]

Figure 1. Simulated frequency responses of proposed DBPF.

FDP-22

Comparison of Power Handling Capabilities of Double-Strip Resonator Filters with Stripline Structure and Conventional Microstrip Line Filters

N. Sekiya*, H. Matsuura

(University of Yamanashi) The power handling capability of a superconducting transmit filter with a double-strip resonator was investigated by comparing the performances of such a filter with conventional microstrip-line filter. The double-strip resonator structure consists of two coupled strips and feed lines. The idea is to increase the effective film thickness to reduce the current concentration at the edges of the resonator compared with that of a conventional single-strip resonator [1]. The filters had three-pole half-wavelength straight-line resonators, a 5.0-GHz center frequency, and a 100-MHz bandwidth. They were fabricated using YBa2Cu3O7 thin films on an r-Al2O3 substrate. The back of the substrates were Au coated for the ground plane. Figure 1 shows the measured and simulated frequency responses of the proposed double-strip resonator filter. The measured frequency responses of the filter were in reasonable agreement with the simulated ones. The measured power handling capability of the proposed filter was larger than that of the conventional filter. The details will be reported at the symposium. [1] N. Sekiya, H. Matsuura, M. Akiya, Y. Tanaka, S. Ohshima, “Novel HTS double-strip resonator for high power

application,” IEEE Trans. Appl. Supercond., vol. 17, no. 2, 1500904, 2013

Figure 1. Measured and simulated frequency responses of double-strip resonator filter.

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0

4.6 4.8 5 5.2 5.4

measured S11measured S21simulated S11simulated S21

S11

, S21

[dB

]

Frequency [GHz]

FDP-23

Power Reduction of Rf-SQUID Memory Cell Using Stochastic Resonance

Ryosuke Kihara

*1, Yuki Yamanashi

1, Nobuyuki Yoshikawa

1

(1Yokohama National University)

An rf-SQUID can be used as a digital memory cell in the superconducting computation systems. In the memory

system, large amount of power is consumed by the decoders that select one of memory cells and data input to the

cell. We have investigated power reduction of the data input to the rf-SQUID memory cell by using stochastic

resonance phenomenon in the SQUID.

We have simulated read/write operation of the rf-SQUID memory cell taking influences of the white current

noises into account and found that the datum can be read and written to the memory cell properly under the

appropriate condition in which the stochastic resonance occurs. Moreover, the total power consumption of the

read/write can be reduced because the applied noise assists the state transition of the SQUID. Fig. 1 shows the

simulated dependences of the success rate of the read/write operation of the rf-SQUID memory cell on the

amplitude of the applied noises. By choosing appropriate parameters such as the noise amplitude, operation speed,

and circuit parameters, we can build the low-power SQUID memory cell.

We have designed the 1-bit rf-SQUID memory cell using the AIST 2.5 kA/cm2 Nb standard process 2 [1], and

tested the cell by applying noise from the room-temperature instruments. We have experimentally observed the

stochastic resonance in the rf-SQUID memory cell.

This work was supported by JSPS KAKENHI Grant Number 25820137 and JST-ALCA. The devices were

fabricated in the clean room for analog-digital superconductivity (CRAVITY) in National Institute of Advanced

Industrial Science and Technology (AIST).

[1] M. Hidaka, S. Nagasawa, T. Satoh, K. Hinode and Y. Kitagawa, Supercond. Sci. Technol., vol.19, pp.

S138-S142, 2006.

Figure 1. Simulated dependences of the success rate of the read/write operation of the rf-SQUID memory cell on

the amplitude of the applied noises. The noise amplitude is normalized by the Josephson energy of the

Josephson junction, EJ, comprising the rf-SQUID.

FDP-24

Performance Estimation and Design of High-Sensitive Superconductive Digital Magnetometer

Fumihiro China

*,1, Yuki Yamanashi

1, Nobuyuki Yoshikawa

1

(1Yokohama National University)

Digital SQUID magnetometers based on single flux quantum (SFQ) technology have being studied [1]. The

digital SQUID has an extremely high slew rate and a wide dynamic range compared with the analog SQUID

magnetometer [2]. However, the magnetic flux resolution of the proposed digital SQUID was limited to 0.

We have been developing a high-sensitive superconductive digital magnetometer using finite voltage state

dc-SQUIDs. Fig. 1 shows a circuit schematic of the high-sensitive superconductive digital magnetometer. The main

components are two finite voltage state dc-SQUIDs (the SQ1 and SQ2), an SFQ up/down counter, and the magnetic

flux tank circuit for the on-chip flux locked loop (FLL) circuit [3]. The SQ1 and SQ2 continuously output the SFQ

pulse trains to the up/down counter and the magnetic flux tank circuit. The measured magnetic flux is input to the

SQ1 and SQ2. The change of the input magnetic flux is detected by measuring the differences of SFQ output

frequencies between the SQ1 and SQ2 using up/down counter. The magnetic flux tank circuit accumulates flux

quanta and applied the feedback flux to the SQ1 and SQ2.

We have analytically evaluated performances of the high-sensitive superconductive digital magnetometer such

as the magnetic flux resolution, the dynamic range, and the slew rate. The performances depend on the circuit

parameter of the two dc-SQUIDs and magnetic flux tank circuit. The analyzed performances show the good

agreement with the ones obtained by the circuit simulations.

We have designed the high-sensitive superconductive digital magnetometer. Details of the circuit design and

experimental results will be presented.

This work was supported by JSPS KAKENHI Grant Number 25820137 and JST-ALCA. The devices were

fabricated in the clean room for analog-digital superconductivity (CRAVITY) in National Institute of Advanced

Industrial Science and Technology (AIST).

[1] O. Mukhanov, D. Gupta, A. Kadin and V. Semenov, Proc. IEEE, vol. 92, pp. 1564-1584, 2004

[2] S. Linzen, A. Chwala, V. Schultze, M. Schulz, T. Schuler, R. Stolz, N. Bondarenko and H. G. Meyer, IEEE

Trans. Appl. Supercond., vol. 17, pp. 750-755, 2007.

[3] H. Myoren, Y. Kimimoto, K. Terui, and T. Taino, IEEE Trans. Appl. Supercond., vol . 21, pp. 387-390, 2011.

Fig. 1. The circuit schematic of the high-sensitive digital magnetometer

FDP-25

Design and test of component circuits of an integrated quantum voltage noise source for Johnson noise thermometry

T. Yamada＊, M. Maezawa and C. Urano

(National Institute of Advanced Industrial Science and Technology) We present design and test results on component circuits of an integrated quantum voltage noise source (IQVNS) based on rapid single flux quantum (RSFQ) circuits. Johnson noise thermometry (JNT), based on the Johnson-Nyquist formula, is one of the most promising types of primary thermometry because it is applicable to a wide temperature range [1]. As a main component of a JNT system, previously we proposed an IQVNS [2]. The purpose is precise measurements of the triple point of the water, 273.16 K, using a 100-ohm resistance temperature detector. The IQVNS was broken down into three main components: a pseudo random number generator (PRNG), a counter-forwarding-type variable pulse number multiplier (VPNM) and a voltage multiplier (VM) [3]. The CONNECT cell library was used for the circuit design. The circuits were fabricated using the AIST standard II process in the clean room for analog-digital superconductivity of AIST. The test results showed the correct operation of a 17-bit PRNG with the bias margin ranging from 78% to 124% of the designed value (fig. 1 (a)). We also confirmed the correct operation of an 8-bit VPNM with a multiplication factor 74 with the bias margin ranging from 82% to 118% (fig. 1 (b)).

This work was supported by JSPS KAKENHI Grant Number 25289126. [1] S. P. Benz et al., Metrologia, vol. 48, pp. 142-153, 2011. [2] M. Maezawa, T. Yamada and C. Urano, J. Phys.: Conf. Ser., vol. 507, part 4, p. 042023, 2014. [3] Y. Mizugaki et al., IEEE Trans. Appl. Supercond., vol. 21, no. 6, pp. 3604-3607, 2011.

(a)

(b)

Figure 1. Low-speed test results of (a) the 17-bit PRNG and (b) the 8-bit VPNM.

FDP-26

4-bit Bipolar Triangle Voltage Waveform Generator Using Single-Flux-Quantum Circuit

T.Watanabe

*,1, Y. Takahashi

1, H. Shimada

1, M. Maezawa

2, Y. Mizugaki

1

(1 The University of Electro-Communications (UEC Tokyo),

2National Institute of Advanced Industrial Science and Technology (AIST))

Josephson junctions generate highly accurate voltage through the Josephson effect. Single-flux-quantum (SFQ)

circuits which consist of superconducting loops and Josephson junctions also generate highly accurate voltage. We

have proposed SFQ digital-to-analog converters (DACs) based on frequency modulation (FM) of SFQ pulse trains

[1-3] to develop new ac voltage standards.

Our previous SFQ-DACs generated only positive voltages, while bipolar output is required for applications of

ac voltage standards. In this paper, we present our design of a 4-bit bipolar triangle voltage waveform generator

comprising an SFQ-DAC. Figure 1 shows a test setup and a microphotograph of a 4-bit bipolar triangle voltage

waveform generator. The 4-bit bipolar triangle voltage waveform generator consists of a 3-bit variable-pulse

number multiplier (V-PNM), two 4-fold voltage multipliers (VMs), and a code generator (CG). The differential

voltage V1 – V2, where V1 and V2 are respectively the output voltages of VM1 and VM2, is used as bipolar output

voltage. The V-PNM generates SFQ pulse trains in which the number of SFQ pulses are multiplied according to a

digital code. The code generator generates the digital codes which modulate the frequency of the SFQ pulse train

and select a working VM. Unipolar triangle voltage waveforms are alternately generated in the VMs. Then, the

differential voltage of two VMs becomes a bipolar triangle voltage waveform. We have confirmed the generation of

bipolar triangle voltage waveforms.

The authors thank Y.Urai and M.Moriya for fruitful discussions and technical supports. The circuits were

fabricated in the clean room for analog-digital superconductivity (CRAVITY) of National Institute of Advanced

Industrial Science and Technology (AIST) with the standard process 2 (STP2). This work was partially supported

by VLSI Design and Education Center (VDEC), the University of Tokyo in collaboration with Cadence Design

Systems, Inc.

[1] Y. Mizugaki, et al., IEEE Trans. Appl. Supercond., 23 (2013) 1300804.

[2] Y. Takahashi, et al., IEICE Trans. Electron., E97-C (2014) 194.

[3] Y. Mizugaki, et al., Jpn. J. Appl. Phys., 53 (2014) 053101.

Figure 1. (a) Test setup and (b) microphotograph of a 4-bit bipolar triangle voltage waveform generator.

FDP-27

High-speed Demonstration of an SFQ-based Computing System for Solving 3n+1 Problem

Qiuyun Xu

*,1, Xizhu Peng

1, Yuki Yamanashi

1, Thomas Ortlepp

2 and

Nobuyuki Yoshikawa1

(1Yokohama National University, Yokohama, Japan

2CiS Research Institute, Erfurt, Germany)

With tremendous high-energy efficiency, when compared to CMOS technology, SFQ logic families comprise a

promising perspective in solving complex mathematical problems, which require numerous periodic computations

while the algorithm itself is simple. Among those unsolved mathematic conjectures, we investigate the 3n+1

problem, which is to take any natural number n and develop a series of repeated iterations, and no matter which

number initiates the sequence, the outcome will be 1. We use this example to demonstrate an SFQ-based computing

system with a processor and memories, and to evaluate the energy efficiency of the system. In the present study, we

designed and implemented an SFQ-based computing system for solving the 3n +1 problem by using the AIST 10

kA/cm2 advanced Nb process. The system consists of a central processor, two 16-bit register files and a

high-frequency clock generator. The maximum clock frequency and the total power consumption of the designed

system are estimated to be 90 GHz and 0.85 mW, respectively. In the previous study, we showed the correct

operation of the system at low speed, and in this paper, we will demonstrate the high-speed test results of the

system.

Acknowledgment:

The CONNECT ADP cell library and tools were used in this study. The circuits were fabricated in the clean room

for analog-digital superconductivity (CRAVITY) of AIST with the advanced process 2 (ADP2).

Figure 1. Microphotograph of a fabricated SFQ computing system for solving 3n+1 problem.

FDP-28

Adiabatic quantum-flux-parametron cell library with minimalist design

Naoki Takeuchi*,1, Yuki Yamanashi2, Nobuyuki Yoshikawa2

(1NICT, 2Yokohama National University)

Adiabatic quantum-flux-parametron (AQFP) [1] is an extremely energy-efficient logic with the bit energy below thermal noise energy (~ 10-22 J at 4.2 K) [2]. We have demonstrated several AQFP logic circuits using our AQFP cell library [3]. However, each logic cell in the library, as well as that in the rapid single-flux-quantum (RSFQ) cell library [4], needs complex procedures for parameter optimization, which eventually requires a vast amount of time to design and modify the cell library. In principle, any AQFP logic gate can be designed using only four building blocks: buffer, NOT, constant, branch. This means that any robust logic circuits can be realized by combining these building blocks, if the parameters of the blocks are well optimized. In this study, we design AQFP cell library with the minimalist design, where all logic cells are designed only with the four building blocks. The minimalist design enables us to design and modify the cell library easily and fast.

Figure 1 shows examples of logic cells with the minimalist design. The majority gate (Fig. 1(a)) is composed of three buffer gates and a branch. The NAND gate (Fig. 1(b)) is composed of two NOT gates, a constant (“1”) and a branch. The splitter gate (Fig. 1(c)) is composed of a buffer gate and a branch. We have designed and fabricated the AQFP cell library with minimalist design using the Nb Josephson process, the AIST standard process (STP2) [5]. We will report the results of low-speed function tests of the designed cells in the presentation.

[1] N. Takeuchi et al., Supercond. Sci. Technol., vol. 26, no. 3, p. 035010, Mar. 2013. [2] N. Takeuchi et al., Appl.

Phys. Lett., vol. 103, no. 6, p. 062602, 2013. [3] K. Inoue, Master thesis, Yokohama National University, Mar.

2014. [4] S. Yorozu et al., Phys. C., vol. 378–381, pp. 1471–1474, Oct. 2002. [5] S. Nagasawa et al., IEEE Trans.

Appl. Supercond., vol. 5, no. 2, pp. 2447–2452, Jun. 1995.

(a) (b) (c)

Figure 1. Examples of minimalist design. (a) Majority gate. x = ab+bc+ca. (b) NAND gate. x = NOT(ab).

(c) Splitter gate. x = y = z = a.

FDP-29

AC-DC Transfer Measurement with a Sampling Method Based on 10 Vrms AC-Programmable Josephson Voltage Standard

Yasutaka Amagai*,1, Michitaka Maruyama1, Hirotake Yamamori2, Chiharu Urano1,

Hiroyuki Fujiki1, Nobu-hisa Kaneko1

(1National Metrology Institute of Japan, National Institute of Advanced Industrial Science

and Technology, 2Nanoelectronics Research Institute, National Institute of Advanced

Industrial Science and Technology)

Thermal converters are used as a primary means of AC voltage calibration at national measurement laboratories [1]. The difference in the response between AC and DC voltages is defined as the AC-DC transfer difference. The measurement accuracies using thermal converters are limited with the theoretical models describing AC-DC transfer differences. At low frequencies below 100 Hz, thermal converters suffer from technical problems such as increased uncertainty due to the non-linear heat conduction. Compared with others, a sampling method based on a programmable Josephson voltage standard (PJVS) system [2], [3] appears to be most promising approach. However, the limited dynamic range hinders their broad applications such as the calibration of thermal converters and high-precision commercial instruments.

At National Industrial Science and Technology (AIST), a sampling measurement system at the maximum root-mean squared (rms) voltage of 3 V has been developed to characterize the low-frequency properties of thin-film thermal converters so far [4]. Figure 1 shows the preliminary results of measured AC-DC transfer differences for single junction thermal converters with different heater resistance of 25 Ω and 90 Ω below 10 Hz at the rms voltage of 3 V. Further, a 10 Vrms step-wise approximated waveforms have been generated with an AC-PJVS system [5], which enables us to extend the measured voltage range up to the voltage of 10 Vrms.

In this study, we have extended a dynamic range of our sampling measurement system for AC-DC transfer measurements using 10 Vrms AC-PJVS system, in order to evaluate the low-frequency properties of thermal converters. In the conference, the measurement results of AC-DC transfer differences up to 10 Vrms will be presented.

[1] B. D. Inglis, Metrologia, Vol. 29, pp. 191–199, Nov. 1992. [2] A. Rüfenacht et al., IEEE Trans. Instrum. Meas., vol. 58, no. 4, pp. 809–815, April 2009. [3] A. Rüfenacht et al., IEEE Trans. Instrum. Meas., vol. 62, no. 6, pp. 1587–1593, June 2013. [4] Y. Amagai et al., IEEE Trans. Instrum. Meas., vol. 62, no. 6, pp. 1621–1626, June 2013. [5] M. Maruyama et al., Proc. CPEM Dig., August 2014 (In press)

Figure 1. Measured AC-DC transfer differences below 10 Hz at the rms voltage of 3 V using sampling method

based on AC-PJVS system.

-500

0

500

1000

1500

2000

2500

1 10 100

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-DC

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/V)

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FDP-30

Heat Transfer Analysis of a Programmable Josephson Voltage Standard Chip Operated with Mechanical Cooler

Hikari Takahashi*,1, Michitaka Maruyama2, Yasutaka Amagai2, Hirotake Yamamori2,

Nobu-hisa Kaneko2 , Shogo Kiryu1

(1Tokyo City University, 2National Institute of Advanced Industrial Science and Technology)

We are developing a programmable Josephson voltage standard (PJVS) system using a 10 K mechanical cooler

which enables liquid-helium free operation. The PJVS chip is composed of 524 288 NbN-based superconductor-

normal metal-superconductor (SNS) Josephson junctions. The junctions are fabricated on a Si chip with a size of 15

mm×15 mm, bonded on a sapphire substrate using InSn solder. In our previous experiments, we found a problem

that the operation margin cloud be affected by the heating effect of the chip depending on the output voltage level.

In this study, we carried out a heat transfer analysis for the PJVS chip by computer simulation using the finite element

method.

In order to construct a model for analysis, we made observations of a PJVS chip with a scanning acoustic

microscope (SAM), etc. It was shown that there were a lot of voids in the InSn solder layer. The ratio of the voids

are estimated to be about 80 % of the surface area of the chip. Additionally, it was found that the thickness of the

InSn layer was 8 μm (±4 μm) from the cross-sectional observation. Based on these results, we constructed a donut

model in which the center of InSn layer is hollow. We then examined the relationship of the ratio of voids and the

maximum temperature on the PJVS chip surface using the donut model. Figure 1 illustrates the results of analysis.

The obtained plots for the area ratio of voids in the InSn layer (r) versus the maximum temperature in the chip

(Tmax) are well coincide with the function: Tmax = 0.945/(100 − r) + 10. The maximum temperature diverges as the

ratio goes up and reaches about 10.1 K when the ratio exceeds 80 % of the chip area. This value of temperature rise

seems to be consistent with the experimental value obtained in our previous study. We are now proceeding more

detailed analyses.

Figure 1. Relationship between voids ratio in the InSn layer and the maximum temperature on the PJVS chip

surface calculated with a donut model as shown in the inset.

0 20 40 60 80 100

10

10.1

10.2

10.3

Voids ratio in InSn layer ( r) [%]

Ma

xim

um

te

mp

era

ture

on

th

eP

JV

S c

hip

su

rfa

ce

(T

ma

x) [

K]

FDP-31

Four-channel ULF-MRI System in Unshielded Urban Laboratory

Environment

Hui Dong*,1, Chao Liu1, Longqing Qiu1, Baolin Chang1, Xiaoming Xie1

(1State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of

Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai

200050, China) Ultra-low field (ULF) magnetic resonance imaging (MRI), which obtains images in the static magnetic field typically at the orders of tens to hundreds of µT. ULF MRI exhibits potential advantages, such as enhanced longitudinal relaxation time (T1) contrast and the combination with magnetoencephalography (MEG) system1. However, the ULF MRI system faces the challenge of poor signal-to-noise ratio (SNR). Beside the introduction of prepolarization technique and the usage of extremely sensitive superconductor quantum interference devices (SQUID), the multi-sensor parallel imaging technique can also improve the SNR and allow accelerated image acquisition. The ULF MRI systems are usually built in shielded rooms for noise reduction, which may face the eddy current transient problem. In this work, a four-channel ULF MRI system was built in urban laboratory without shielding using 2nd-order low-Tc SQUID gradiometers. The unshielded system benefits the A permanent magnet pair with a field strength of 0.65 T was utilized for sample pre-polarization to improve the SNR. An active compensation technique was developed to stabilize the temporal environmental field fluctuation2. The environmental gradient field tensor was compensated by a full-tensor gradient field compensation3. Using the standard Fourier imaging method and the weighted image superposition algorithm, the two-dimensional (2D) and three-dimensional (3D) four-channel MRI images of pepper pieces were obtained at the static field of 129 T, i.e. the Larmor frequency of 5.5 kHz. The 2D in-plane resolution of about 2 mm 2 mm is achieved. These results demonstrated the feasibility of performing 2D and 3D multi-sensor parallel ULF-MRI imaging in the unshielded urban environment.

[1] J. Clarke, M. Hatridge and M. Moessle, Annu. Rev. Biomed Eng. 9 (2007) 389. [2] L. Qiu, C. Liu, H. Dong, et al., Phys. Procedia 36 (2012) 388. [3] H. Dong, L. Qiu, W. Shi, et al., Appl. Phys. Lett. 102 (2013) 102602.

Figure 1. Ultra-low field MRI system built in unshielded laboratory.

PM pair

Electric Actuator

SQUID

FDP-32