First-principles study on the electron-phonon coupling and magnetoresistance of LaBi under pressure

TL;DR

This study uses first-principles calculations to investigate the electron-phonon coupling and magnetoresistance of LaBi under pressure, revealing structural transitions and questioning the phonon-mediated superconductivity mechanism.

Contribution

It provides a detailed theoretical analysis of LaBi's electronic structure, magnetoresistance, and phase transitions under pressure, challenging previous assumptions about its superconductivity mechanism.

Findings

LaBi undergoes a structural phase transition at ~7 GPa.

LaBi remains topologically nontrivial across the transition.

Weak electron-phonon coupling cannot explain the observed superconductivity.

Abstract

The extremely large magnetoresistance (XMR) material LaBi was reported to become superconducting under pressure accompanying with suppressed magnetoresistance. However, the underlying mechanism is unclear. By using first-principles electronic structure calculations in combination with a semiclassical model, we have studied the electron-phonon coupling and magnetoresistance of LaBi in the pressure range from 0 to 18 GPa. Our calculations show that LaBi undergoes a structural phase transition from a face-centered cubic lattice to a primitive tetragonal lattice at $\sim$7 GPa, verifying previous experimental results. Meanwhile, LaBi remains topologically nontrivial across the structural transition. Under all pressures that we have studied, the phonon-mediated mechanism based on the weak electron-phonon coupling cannot account for the observed superconductivity in LaBi, and the calculated magnetoresistance for LaBi does not show a suppression. The distinct difference between our calculations and experimental observations suggests either the existence of extra Bi impurities in the real LaBi compound or the possibility of other unknown mechanism.