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Please use this identifier to cite or link to this item: http://arks.princeton.edu/ark:/88435/dsp01qj72pb52x
Title: Phase sensitive transport measurements on exotic superconductors
Authors: Zhu, Zheyi
Advisors: Ong, Nai Phuan
Contributors: Physics Department
Subjects: Physics
Issue Date: 2024
Publisher: Princeton, NJ : Princeton University
Abstract: The phase of the order parameter in superconductivity is a fundamental concept that explains the coherent quantum state of the electron pairs across the superconductor. Probing the phase of the order parameter in superconductors is essential for understanding and utilizing their unique quantum properties. This thesis presents two different transport experiments that investigate the order parameter phase in two exotic superconductivity systems, respectively. The first system is MoTe2, a type-II Weyl semimetal that exhibits superconductivity at ultra-low temperatures. The interplay between topological band structure and superconducting pairing condensate has attracted considerable interest. We investigated the planar Al-MoTe2-Al Josephson junction using the asymmetric SQUID technique to simultaneously achieve control of the phase difference across the junction and the proximity effect from s-wave aluminum superconductivity into MoTe2. We observed subharmonic gap structure in the finite voltage regime of the MoTe2 junction and attributed it to multiple Andreev reflection (MAR). Additionally, we explored the phase tuning of MAR both above and below the critical temperature Tc of MoTe2. Coherent supercurrent transport inferred from MAR is discussed. The second system is infinite-layer nickelates Nd1-xSrxNiO2, an unconventional type-II superconductor isostructural to well-known high-Tc cuprate superconductors. An Abrikosov vortex in a Type-II superconductor under a magnetic field carries one quantum of magnetic flux and exhibits a 2π phase singularity. The dynamics of these vortices under electric current or thermal gradient provide critical insights into the superconductivity of these materials. We investigated the thermoelectric response in Nd1-xSrxNiO2 thin film subjected to a vertical magnetic field and observed a significant nonlinear Nernst effect in extended temperature regime, even above Tc. This Nernst signal, identified as vortex Nernst effect, arises from the movement of vortices with 2π phase singularity and generates an electric field through the Josephson effect. With the revealed information on superconducting parameter phase, we provide evidence of vortex-liquid phase in nickelates, which shows a strong similarity to that of high Tc cuprates.
URI: http://arks.princeton.edu/ark:/88435/dsp01qj72pb52x
Type of Material: Academic dissertations (Ph.D.)
Language: en
Appears in Collections:Physics

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