Date of Award

8-2025

Degree Name

Doctor of Philosophy

Department

Physics

First Advisor

Clement Burns, Ph.D.

Second Advisor

Lisa Paulius, Ph.D.

Third Advisor

Asghar N Kayani, Ph.D.

Fourth Advisor

Pnina Ari-Gur, D.Sc.

Keywords

Anisotropic energy gaps, AuPb3, noncentrosymmetric superconductors, spin orbit coupling

Abstract

AuPb3 is a non-centrosymmetric superconductor that crystallizes in a tetragonal structure and undergoes a superconducting transition at 4.4 K. Non-centrosymmetric superconductors that lack inversion symmetry are predicted to have an admixture of spinsinglet and spin-triplet symmetry induced by strong antisymmetric spin-orbit coupling (ASOC).

In this work, we investigated the normal and superconducting properties of AuPb3. We also carried out the Density Functional Theory (DFT) calculations to study the strength of ASOC and its impact on vibrational and electronic properties. A high-quality polycrystalline sample of AuPb3 was grown and characterized by powder x-ray diffraction, scanning electron microscopy, magnetization, specific heat, and electrical resistivity measurements.

The results show AuPb3 is a Type II superconductor with an upper critical field less than the Pauli limit. The normalized electronic specific heat capacity jump is larger than predicted by the Bardeen-Cooper-Schrieffer (BCS) theory. The results from specific heat measurements at temperatures down to 100 mK show power law dependence or two-gap behavior rather than the exponential fall-off predicted by BCS theory. The Sommerfeld coefficient γ0 in the superconducting state shows the nodal behavior with field dependence γ0 „ ? H. Furthermore, in the normal state, we observed a large magnetoresistance (over 700%) and a saturating electrical resistivity at higher temperatures. The calculations show the average strength of ASOC is ~ 135 meV, and there is significant electron-phonon coupling in the normal state of the material.

Access Setting

Dissertation-Open Access

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