"Measurements of nonequilibrium interatomic forces using time-domain x-ray scattering"

Samuel W. Teitelbaum: Thomas C. Henighan, Hanzhe Liu, Mason P. Jiang, Diling Zhu, Matthieu Chollet, Takahiro Sato, Éamonn D. Murray, Stephen Fahy, Shane O’Mahony,Trevor P. Bailey , Ctirad Uher, Mariano Trigo, and David A. Reis; Physical Review B, 05/18/21.

Additional Authors: Thomas C. Henighan, Hanzhe Liu, Mason P. Jiang, Diling Zhu, Matthieu Chollet, Takahiro Sato, Éamonn D. Murray, Stephen Fahy, Shane O’Mahony,Trevor P. Bailey , Ctirad Uher, Mariano Trigo, and David A. Reis

Abstract:

We demonstrate an experimental approach to determining the excited-state interatomic forces using femtosecond x-ray pulses from an x-ray free-electron laser. We determine experimentally the excited-state interatomic forces that connect photoexcited carriers to the nonequilibrium lattice dynamics in the prototypical Peierls-distorted material, bismuth. The forces are obtained by a constrained least-squares fit of a pairwise interatomic force model to the excited-state phonon dispersion relation as measured by the time- and momentum-resolved x-ray diffuse scattering. We find that photoexcited carriers weaken predominantly the nearest-neighbor forces, which drives the measured softening of the transverse acoustic modes throughout the Brillouin zone as well as the zone-center A1g optical mode. This demonstrates a bond-selective approach to measuring electron-phonon coupling relevant to a broad range of photoinduced phase transitions and transient light-driven states in quantum materials.