1. 𝜆 =
𝑚∗
𝜇 𝑜 𝑒2 𝑛 𝑠
3He pot
3K rod
Pressure TDR
Circuit
BCS Theory (Conventional)
Setup
Work at the Ames Laboratory was supported by the U.S. Department of Energy Office of Science, Science Undergraduate Laboratory Internships (SULI) program under its contract with Iowa State University, Contract No. DE-AC02- 07CH11358. John Patrick Guss is grateful to the DOE for the assistantship and opportunity to participate in the SULI program.
Measuring Magnetic Properties of Superconductors
Under Pressure and down to ~500 mK
John Guss, D. Motes, S. Teknowijoyo, E. Timmons, M. A. Tanatar, R. Prozorov, Kyuil Cho
Motivation
Background Methods Results
Future work
References
Under an applied magnetic field, a certain extent
of the field still penetrates a superconductor
phonon mediated interaction
 Paired electrons condense to the lower
energy state opening a gap near the Fermi
energy
 Most elemental
superconductors are of
conventional s-wave.
 Certain directions have
zero superconducting
gap called nodes
Calculating the London Penetration Depth
∆𝜆 = −
𝑅
Δ𝑓𝑜
𝛿∆𝑓
Change in frequency due to change in
magnetic property of a superconductor
Pullout factorChange in London
Penetration Depth
Effective Sample Size
C. Poole et al., Superconductivity. London: Elsevier, 2007. Print.
C. T. Van-Degrift, Rev. Sci. Instrum. 46(5), 599 (1975).
K. Cho et al., Phys. Rev. B 86, 020508 (2012).
R. Prozorov et al., Journal of Phys.: Conf. Series 449, 012020 (2013).
R. Prozorov et al., PRB 62, 115 (2000); APL 77, 4202 (2000); PRL 85,
3700 (2000).
R. Prozorov et al., Supercond. Sci. Technol. 19, R41 (2006).
R. T. Gordon, Ph.D Dissertation (2011).
𝑓 =
1
2𝜋 𝐿𝐶
Previous results down to 1.8 KProperties of Superconductors
 Zero electrical resistance below a critical temperature, 𝑇𝑐
 Expels external magnetic fields (Meissner effect) below 𝐵𝑐
Superconducting gap
London Penetration Depth(λ)
Conventional s-wave Unconventional d-wave
Tunnel Diode Resonator (TDR) Circuit
Lead
Sample
The base temperature with TDR operation  500mK
Thermal insulation achieved with vacuum chamber
Unconventional multiband (s+-)
Nodal Gap
Superconducting
gap
Full Gap
Number of
Superconducting
electrons
Pressure
Cell
Thermometer
3K Plate
 Measurement of penetration depth under applied pressure will provide
insight into the mechanisms of unconventional superconductors.
 Various tuning parameters – chemical substitution, applied magnetic
field, pressure, etc.
 The pressure is a “clean” tuning parameter.
New results down to 500 mK
 We will continue our development to achieve clean
background subtraction.
 We would like to see the effect of pressure on the
superconducting gaps of FeSe and (Ba1-xKx)Fe2As2
superconductors.
Now we can measure penetration depth down to 500 mK under pressure.
Lead sample
Background data
Cooper Pairing
Silver Epoxy
connections
Bender Unit
 Closed cycle liquid Helium-3 cryostat
 No consumption of liquid Helium (Cryogen-free)