Phonon second harmonic generation in NaBr studied by inelastic neutron scattering and computer simulation
-
1.
California Institute of Technology
-
2.
Oak Ridge National Laboratory
Abstract
The phenomenon of second harmonic generation (SHG) was found for phonons in anharmonic NaBr by inelastic neutron scattering. The temperature dependence of this phonon SHG was measured from 300 K to 650 K. At 300 K the second harmonic (SH) is seen as a high-energy branch around 33 meV, nearly independent of Q. The temperature effective potential (TDEP) method and classical molecular dynamics (MD) simulation with machine learning interatomic potential were able to reproduce the SH, and showed that SHG occurs with the flat transverse optical (TO) phonon branch. A classical model of a nonlinear medium explains the intensity and lifetime of the SH, compared to those of the TO modes. Also successful was a quantum model based on the Heisenberg-Langevin equation for interacting phonons coupled to a thermal bath, which also predicts a spectral distribution of the SH. The measured temperature dependence of the intensity of the second harmonic showed that it follows the Planck distribution of a one-phonon quasiparticle, and not two TO phonons.
Copyright and License
©2025 American Physical Society.
Acknowledgement
This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. In addition, this work used resources from the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Finally, this work was supported by the DOE Office of Science, BES, under Contract No. DE-FG02-03ER46055. The work by M.E.M. was supported by the U.S. DOE Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.
Supplemental Material
Supplemental provides information on experimental and computational procedures.
It includes details of single crystal data processing, peak fitting, and intensity analyses; computational details of temperature-dependent effective potential computation and autocorrelation function calculation.
Files
Additional details
- United States Department of Energy
- DE-AC02-05CH11231
- United States Department of Energy
- DE-FG02-03ER46055
- Accepted
-
2025-01-16
- Caltech groups
- Division of Engineering and Applied Science (EAS)
- Publication Status
- Published