First principles calculations of noncentrosymmetric superconductors

Abstract

The asymmetric spin-orbit coupling (ASOC) of a noncentrosymmetric superconductor (NCS) arises due to lack of inversion symmetry and leads to a mixed singlet/triplet Cooper pairing in the superconducting state and other exotic properties. In this work, the electron behaviour of two noncentrosymmetric materials with the same symmetry of tetragonal crystal structure, LaPdGe₃ and LaPtSi₃ are studied. These two materials are electronically expected to be similar, but LaPdGe₃ is a not a superconductor. Density functional theory is used to calculate the band structure and Fermi surface for both materials and the effects of uniaxial pressure applied on c and a,b-axis is investigated, respectively. The calculations show that the ASOC of LaPtSi₃ is stronger than that of LaPdGe₃, and for both materials the strength of ASOC will open a band gap, for LaPdGe₃ it is 0.15 eV, and for LaPtSi₃ it is 0.5 eV, which causes the Fermi surface splitting and a pocket appears at the Γ point. At the same time ASOC will increase with pressure applied in a,b-axis.

Date of Award	6 Dec 2022
Original language	English
Awarding Institution	University of Bristol
Supervisor	Martin Gradhand (Supervisor) & James F Annett (Supervisor)