NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds

TL;DR

This study uses NMR spectroscopy and first-principles calculations to reveal how relativistic effects influence the bulk electronic structure of half-Heusler compounds, providing evidence for their topologically nontrivial nature.

Contribution

It demonstrates that 209Bi NMR isotropic shifts can detect relativistic effects on band structures, offering a bulk-sensitive method to study topological properties.

Findings

209Bi NMR shifts scale with spin-orbit coupling strength

Relativistic p1/2 and p3/2 states significantly affect NMR parameters

NMR provides bulk electronic structure insights complementary to surface methods

Abstract

Spin-orbit coupling (SOC) is expected to partly determine the topologically nontrivial electronic structure of heavy half-Heusler ternary compounds. However, to date, attempts to experimentally observe either the strength of SOC or how it modifies the bulk band structure have been unsuccessful. By using bulk-sensitive nuclear magnetic resonance (NMR) spectroscopy combined with first-principles calculations, we reveal that 209Bi NMR isotropic shifts scale with relativity in terms of the strength of SOC and average atomic numbers, indicating strong relativistic effects on NMR parameters. According to first-principles calculations, we further claim that nuclear magnetic shieldings from relativistic p1/2 states and paramagnetic contributions from low-lying unoccupied p3/2 states are both sensitive to the details of band structures tuned by relativity, which explains why the hidden relativistic effects on band structure can be revealed by 209Bi NMR isotropic shifts in topologically nontrivial half-Heusler compounds. Used in complement to surface-sensitive methods, such as angle resolved photon electron spectroscopy and scanning tunneling spectroscopy, NMR can provide valuable information on bulk electronic states.