Magnetic Field Profile in Classical Superconductors

Vladimir Kozhevnikov, Tulsa Community College, DMR 0904157

0 30 60 90 120 1500.1

1

local theory

scre

en

ed

fie

ld/a

pp

lied

fie

lddepth (nm)

2.87 K 3.02 K 3.20 K

SN0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50

20

40

60

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two-fluid model

theory: 25 nmTc

L(0)=(28 ± 4)nm

Lo

nd

on

pen

etra

tio

n d

epth

(n

m)

temperature (K)

IN

The field profile in Sn measured with Low-Energy MuonsInsert: the London penetration depth data obtained from PNR (red point) and LE-mSR (brown pp.) measurements.

Superconductivity is (perhaps) the most fascinating and (for sure) the most challenging phenomenon with enormous potentials for applications. Examples of the current applications are MRI and Large Hadron Collider. This year is 100 anniversary of its discovery. However, in spite of many outstanding achievements (marked by 10 Nobel Prizes!), the field still keeps lots of secrets. One of the longest standing challenges is quantitative measurements of in-depth distribution of magnetic filed penetrating into superconductors in the Meissner state. This is the goal of our project. Such measurements pave the most direct way to “the chief parameters”, such as the London penetration depth and the Pippard coherence length, controlling microscopic properties of superconductors. Neither of these parameters is known for any superconductor. This year we completed, for the first time, such measurements on In (see insert), using Low-Energy Muon Spin Rotation spectroscopy (LE-SR) and Polarized Neutron Reflectometry (PNR), and performed LE-SR experiment on Sn. Cross LE-SR and PNR measurements are necessary to ensure reliability of results and quantify their uncertainties. The data obtained agree with each other and firmly support nonlocal Pippard and BCS theories, predicting nonexponential decay of the penetrating magnetic field.

Magnetic Field Profile in Classical Superconductors

Vladimir Kozhevnikov, Tulsa Community College, DMR 0904157

Tulsa Community College is a two-years college of primary high education. TCC students involved in the project take a special class “Selected topics in physics”, where they study foremost topics of physics, staying beyond the standard curriculum of college physics classes. Students completed the class have their tuition reimbursed from the grant. The most active students participated in the neutron’s experiments in Chalk River Labs, Canada (winter 2010) and muon’s experiments in Paul Scherrer Institute, Switzerland (summer 2010 and summer 2011). The students took part at the APS March Meetings in 2010 and 2011, and at the Oklahoma Research Day conference (Cameron University, OK, 2010, 2011). All travel expenses are covered from the grant. As of today (August/2011) the class has been offered for three semesters; total 11 students graduated the class.

Students of the Special Topics class Jon Snellgrove and Sasha Townsend give a talk about the Standard Model (Spring 2011)

One former student is currently employed in the Science and Math division at TCC, Metro; other students continue their education in STEM specialties at universities of Oklahoma.

Articles about this education opportunity appeared in TCC news and in The Tulsa World newspaper (2/21/2011).

Last Spring the PI gave a college-wide lecture devoted to 100 years of superconductivity which was attended by more than 60 students. The lecture recording will be soon available at the Science and Math Division website.