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Van Harlingen, Dale J Mason, Nadya Fradkin, Eduardo H Filippini, Jeffrey P Hamilton, David Robert 2019-11-26T20:49:14Z 2019-11-26T20:49:14Z 2021-11-27T10:15:30Z 2019-06-20 2019-08 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$_{2-x}$Ba$_x$CuO$_4$ (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$_{2−x}$Sr$_x$CuO$_4$ (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. Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2021-08-01 The student, David Hamilton, accepted the attached license on 2019-06-19 at 13:38. The student, David Hamilton, submitted this Dissertation for approval on 2019-06-19 at 13:58. This Dissertation was approved for publication on 2019-06-20 at 12:13. DSpace SAF Submission Ingestion Package generated from Vireo submission #14058 on 2019-11-26 at 13:03:35 Made available in DSpace on 2019-11-26T20:49:14Z (GMT). No. of bitstreams: 2 HAMILTON-DISSERTATION-2019.pdf: 16119177 bytes, checksum: b32dc24a57c990db4a23f81d5b61d314 (MD5) LICENSE.txt: 4211 bytes, checksum: 1f5f9b62c8f9ef534f1a8f9ada6de4ce (MD5) Previous issue date: 2019-06-20 Embargo set by: Seth Robbins for item 112903 Lift date: 2021-11-26T20:49:41Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system U of I Only Restriction Lifted for Item 112903 on 2021-11-27T10:15:30Z. application/pdf http://hdl.handle.net/2142/105758 en Copyright 2019 by David Robert Hamilton. All rights reserved. superconductivity josephson effect pair-density wave current-phase relation Exploring exotic superconducting order in La-based cuprate materials using Josephson interferometry text text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.