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Adam Kaminski Ames Laboratory and Iowa State University
High temperature superconductivity - insights from Angle Resolved Photoemission Spectroscopy
Funding:Ames Laboratory - US Department of Energy
Ames Laboratory Spectroscopy Group:
Takeshi Kondo - postdoctoral researcherAri Palczewski - Ph. D. studentJames Koll - undergraduate assistant
Collaborators:
Jörg Schmalian - ISURustem Khassanov - University of Zürich, SwitzerlandJanusz Karpinski - ETH, SwitzerlandJoel Mesot - PSI, SwitzerlandTakafumi Sato - Tohoku University, JapanTakashi Takahashi - Tohoku University, JapanHelene Raffy - Universite Paris-Sud, FranceKazuo Kadowaki - University of Tsukuba, Japan
Outline:
- condensed matter physics - is there anything left to understand?
- properties of conventional and “high temperature” superconductors
- introduction to Angle Resolved Photoemission Spectroscopy
- electronic properties of high temperature superconductors
- new results
condensed matter physics - is there anything left to understand?
all physics covered by electrodynamics + quantum mechanics
fortunately electrons in copper are weakly interacting and can be described by Landau Fermi Liquid model (1:1 correspondence with free electron gas), but in many systems the interactions are strong and current state of the art calculations can deal with ... 7x7 lattice
US penny: 3.1 grams of copper, 2.9x1022 electrons
a DVD has 4x1010 bitsso to store information only about spin for each electron we
need: 7.25 x 1011 DVD’s, but this is clearly not enough to do any meaningful calculations
... but complexity and new phenomena arise from large numbers of interacting particles
SuperconductivityDiscovered in 1911 by Kamerlinght Onnes first in mercury, then many other metals and alloys
resi
stan
ce [O
hm]
temperature [K]
Complete theory (BCS) due to Bardeen, Cooper and Schrieffer in 1957
Superconductivity
pairing + condensation
pair of two electron is a boson
bosons can condense creating
superfluid
In the metals electrical resitance arises due to scattering of the conduction
electrons from defects
E
In BCS the attractive pairing interaction between electrons arises from interaction
with the lattice vibrations (phonons)
In the superconducting state current is being carried by superfluid - condensate of very large
number of electron pairs
AFM
T
carrier concentration
SC
T*
pseudogap
TN
metal
~ 0.15
Tc
High temperature superconductorsDiscovered in 1986 by Bednorz and Müller.
Observed so far only in materials that contain copper oxide.
Superconducting transition temperature (Tc) up to 130K.
BiO
BiO
BiO
BiO
SrOCuOCaCuOSrO
SrOCuOCaCuOSrO
BiO
3.17Å
b
a
c
unit cell
Bi2Sr2CaCu2O 8+x
Pairing mechanism - unknown
θ
z
a or bφ
detector
analyzer
ARPES experiment
sample
High resolution UV beamline at Synchrotron Radiation Center, Wisconsin
undulator
hv
e-800 MeV ring at
Synchrotron Radiation Center
electron analyzer
sample
grating
samplelens
hemisphericalanalyzer
detector2D
photoelectrons
Electron analyzer
... high precision lab-based ARPES system
Energy resolution:~1.2 meV
Angular resolution:0.1 deg.
UV source:1013 photons/sec.
From atoms to solids:
two isolated atoms
two atom molecule
solid
Kittel - “Solid state physics”
Dispersion relation - energy bands
insulator
metal
Kittel - “Solid state physics”
θ
z
a or bφ
detector
analyzer
ARPES experiment
We need:binding energy - Eb initial momentum - ki
sampleEb = E - hv + W
ki||=kf
|| = √2mE/h2 sinθ
ki|=0 for quasi 2D samples
Nor
mal
ized
inte
nsity
-400 -300 -200 -100 0Energy [eV]
typical photoemission spectrum from Bi2212Bi 4f5/2 & 4f7/2
Nor
mal
ized
inte
nsity
-140 -138 -136 -134 -132 -130 -128
Energy [eV]
T=300K T=40K
Sr3d3/2,Sr3d5/2Theta=5 deg, hv=500 eV
Bi 5f1/2 , 5f3/2
Nor
mal
ized
inte
nsity
-355 -350 -345 -340Energy [eV]
Emission angle:
0 deg 10 deg 20 deg 30 deg 40 deg 50 deg
Ca2p1/2, Ca2p3/2hv=500 eV
Nor
mal
ized
inte
nsity
-285 -280 -275 -270 -265 -260
Energy [eV]
Sr3p1/2,Sr3p3/2Theta=5 deg, hv=500 eV
C 1s
T=300K T=40K
valence band
conduction band
150x103
100
50
0
Inte
nsity
[co
unts
/5m
in]
-8 -6 -4 -2 0Energy [eV]
Valence and conduction bands - simplest example: poly Au
Nor
mal
ized
inte
nsity
-0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2Energy [eV]
T=100KT=350K
Au 5d
valence band
conduction band
Eb(k1)"Ef"
hν
E
Ef
W
Electronic structure
k1 kk2
Evac
kf
ARPES spectra
hν
Typical “modern” ARPES data:
ARP
ES In
tens
ity
0.5 0.4 0.3
k (A-1)
E=const Momentum Distribution Curve (MDC)
ARP
ES In
tens
ity-0.3 -0.2 -0.1 0.0
Energy [eV]
k=const Energy Distribution Curve (EDC)
kE
I=<Ψi|A●p|Ψf>2A(k,ω) f(ω)symmetry of Ψ electronic structure
and interactionsA. Kaminski et al., Phys. Rev. Lett. 86, 1070 (2001)
-0.6 -0.4 -0.2 0.0 0.2Energy [meV]
-0.6 -0.5 -0.4 -0.3
ky [A-1]
EDC MDCIntensity plot
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
Ener
gy [
eV]
momentum
Eli Rotenberg, Advanced Light Source
C. G. Olson, D. W. Lynch et al.,Science 245, 731-733 (1989)
Superconducting gap
E
kµ
kf
T>TcT<Tc
2 !
J. C. Campuzano et al., Phys. Rev. B 53, 14737 (1996)
d-wave order parameter
H. Ding et al., Phys. Rev. B 54, 9678 (1996)
-1
0
1
10-1kx [π/a]
(0,0) (π,0)Fermi surface M
M
M
YX
XY
node anti-node
Nor
mal
ized
inte
nsity
-100 -80 -60 -40 -20 0 20 40
Energy [meV]
Superconducting stateLuNi2B2C (Tc=16K)T=9.5K
-15 -10 -5 0 5 10
Energy [meV]
5.0 meV
Laboratory system: Scienta analyzer and He Lamp
S. Souma et al., Nature, 423, 65 (2003)
Text
Collective modes
k,ω
k-q,ω-Ω
e
e
q,Ω
Interaction of electrons with a phonon:
Ashcroft and Mermin “Solid State Physics”
Renormalization effects along nodal direction
T. Valla et al., Science 24, 2110 (1999) P.V. Bogdanov et al., Phys. Rev. Lett. 85, 2581 (2001)A. Kaminski et al., Phys. Rev. Lett. 86, 1070 (2001)
k
-0.20
-0.15
-0.10
-0.05
0.00
Interaction of the electrons with a collective mode
T=40KT=140K
Node
AntinodeΓ Μ
Μ
NA
Mode energy
Based on the dispersion we can conclude that the interaction with the collective mode occurs only in the superconducting state, its energy is constant throughout the Brillouin zone and its strength increases significantly towards the antinode. These properties are consistent with the resonant mode observed by Inelastic Neutron Scattering (INS) experiments.
2.0
1.5
1.0
0.5
0.0
v F [e
V A
ng]
1.00.90.80.70.60.5kx [π/a]
Fermi velocity in the normal state
dispersion in normal and superconducting state
40
30
20
10
0
Vh/V
l
1.00.90.80.70.60.5
kx(π/a)
strength of coupling in the SC state
-1
0
1
10-1kx [π/a]
A. Kaminski et al., Phys. Rev. Lett. 86, 1070 (2001)
-0.3 -0.2 -0.1 0.0
k=(1,0)
k=(1,.365) -0.3 -0.2 -0.1 0.0
k=(.730,0)
k=(.730,.365) -0.3 -0.2 -0.1 0.0
k=(.640,0)
k=(.640,.365) -0.3 -0.2 -0.1 0.0
k=(.550,0)
k=(.550,.365) -0.3 -0.2 -0.1 0.0k=(.450,.365)
k=(.450,0)
-0.3 -0.2 -0.1 0.0
k=(.590,0)
k=(.590,.365)
Binding Energy (eV)
EDC’s in the superconducting state
NodeAntinode
A. Kaminski et al., Phys. Rev. Lett. 86, 1070 (2001)
Properties of the bosonic mode compatibility magnetic phonons
1) isotropic energy ∆+Ω yes yes
2) momentum anisotropy yes yes, recently
3) temperature dependence yes not obvious
4) doping dependence yes not obvious
Collective mode “score” card
Ag on Ag(111)Cu on Cu(111)
Scattering in traditional STM
SPECS website
Autocorrelated (AC) ARPES - new tool in studies of scattering processes
-12 meV
AC ARPES: q-space
Fourier transform
FT STM
J. E. Hoffman et al, Science 295, 466 (2002)
J. E. Hoffman et al, Science 297, 1148 (2002)
K. McElroy et al, Nature 422, 592 (2004)
L. Capriotti et al, PRB 68, 014508 (2003)
R. S. Markiewicz et al, PRB 69, 214517 (2004)
1.0
0.5
0.0
-0.5
-1.0
k x [π /
a]
1.00.50.0-0.5-1.0
kx [π/a]
-12 meV
ARPES intensity map
ARPES data and q-spaceq-space map
1.0
0.5
0.0
-0.5
-1.0
q x [π /
a]
1.00.50.0-0.5-1.0qx [π/a]
q1q2
q3
q4
q6q5
q7
q1q2
q3
q4
q6q5
q7
S(q,!= !0) = "kx,ky
I(k,!) I(k+q,!)
AutoCorrelated (AC) ARPES -
-12 meV
ARPES intensity maps
-12 meV
AC ARPES: q-space
q-space
Comparison of FT STM and AC ARPES
q1
q3
q1
q3
K. McElroy et al, Nature 422, 592 (2004)
U. Chatterjee et al, Phys. Rev. Lett. (submitted)
Conclusions:
- ARPES is an excellent probe to study electronic properties of strongly correlated systems such as heavy fermion systems and high temperature superconductors
- the only relevant feature in electronic structure for high temperature superconductivity is a hole pocket Fermi surface centered at kx=ky=1
- bridging the results from ARPES and FT STM will lead to better understanding of low energy excitations and possibly high temperature superconductivity