Exploring exotic superconducting order in La-based cuprate materials using Josephson interferometry

Josephson junctions are especially useful devices for studying exotic superconducting materials, because the transmission of superconductivity through a junction depends on the difference in phase of the superconducting order parameter across the junction. We present the results of two measurements which involve the fabrication of Josephson junctions on unconventional high-temperature superconductors to study the physical processes which govern novel superconducting states within these materials. The first experiment involves measuring the current-phase relation (CPR) of La_2-xBa_xCuO₄ (LBCO)-Au-Nb Josephson junctions. Using two independent measurement methods, we observe a clear sin(2$\phi$) component of the CPR, a signature of pair-density wave (PDW) order. This component is strongest at x=0.125 doping, where PDW order is believed to be strongest, and increases in magnitude with temperature as conventional superconductivity is suppressed. Likewise, at x=0.155 doping, where PDW order is not expected to dominate, the CPR primarily contains the conventional sin($\phi$) term. Together, these results provide strong support to the prediction that charge, spin and superconducting order intertwine to form a pair-density wave state in LBCO near x=1/8 doping. In the second experiment, we perform Josephson interferometry measurements of the superconducting order parameter of La_2−xSr_xCuO₄ (LSCO) in the heavily overdoped (x$>$0.25) regime. Combining experimental measurements and simulations of I_c(\Phi), we find evidence for granular superconductivity and circulating currents in LSCO near criticality.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2019

Author dc:creator

• Hamilton, David Robert

Contributors dc:contributor

• Van Harlingen, Dale J
• Mason, Nadya
• Fradkin, Eduardo H
• Filippini, Jeffrey P

• superconductivity
• josephson effect
• pair-density wave
• current-phase relation

Statement dc:rights

• Copyright 2019 by David Robert Hamilton. All rights reserved.

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/105758

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/105758