The Influence of Spin-Orbit Interaction on the Electron-Phonon Coupling in Tl-Rich Cubic AuCu3-Type Superconductors: Comparison with La3Tl

Abstract

In this work, the role of spin-orbit coupling (SOC) in ATl(3) (A = Ca, Y, La, and Th) and La3Tl is investigated by theoretical investigation of their structural, electronic, elastic, mechanical, phonon, and electron-phonon interaction properties. The effect of SOC on the electronic band structures of these compounds is that some of the degeneracies at the high symmetry points that would exist in a scalar relativistic calculation without SOC are removed by considering this coupling. The replacement of La and Tl atoms in LaTl3 increases the value of the density of states at the Fermi level N(EF$E_{\text{F}}$) by a factor of 2.1. Furthermore, this replacement makes almost all phonon modes in La3Tl softer than those in LaTl3. Both softer phonon modes and higher N(EF$E_{\text{F}}$) make the electron-phonon interaction in La3Tl much stronger than in LaTl3. The presence of SOC increases the Tc$T_{\text{c}}$ values of LaTl3 by 34% (from 1.151 to 1.542 K) and of ThTl3 by 65% (from 0.479 to 0.793 K), resulting in good agreement with the corresponding experimental values of 1.63 and 0.87 K. The inclusion of SOC also improves the agreement with the experiment for Tc$T_{\text{c}}$ values of CaTl3, YTl3, and La3Tl.