  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.
