Spectroscopic signatures of Kohn anomaly in a topological crystalline insulator
Abstract
Topological crystalline insulators extend the concept of topological insulators by hosting surface states protected by crystallographic symmetry. Their topological phase transitions arise from spin-orbit-driven band inversion in the bulk electronic structure, reshaping the low-energy electronic environment and its coupling to lattice excitations. While the electronic aspects of band topology are well established, the corresponding dynamics of lattice and electron-phonon interactions remain largely unexplored. Here, we report a pronounced softening of a low-energy surface phonon mode across the topological phase transition in Pb0.77Sn0.23Se, revealed by temperature-dependent time-domain terahertz spectroscopy. Unlike the well-known phonon softening in ferroelectrics, this effect does not signal a structural instability but instead reflects electronic reconstruction. We attribute the softening to the spectroscopic manifestations of a Kohn anomaly, indicating a strong coupling between lattice vibrations and Dirac-like surface electrons in the topological phase. Consistently, the phonon linewidth deviates from the standard anharmonic temperature dependence, further evidencing enhanced electron-phonon coupling. The observed changes in phonon frequency and linewidth at around 120 K are consistent with the reported topological phase transition temperature in this material. Our results thus provide a spectroscopic route for the distinct identification of the onset of a topological phase.
Versions
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BibTeX
@misc{li2026spectroscopic,
title = {{Spectroscopic signatures of Kohn anomaly in a topological crystalline insulator}},
author = {Jingwen Li and Arpita Dutta and Kush Saha and Andrzej Szczerbakow and Tomasz Story and Manfred Fiebig and Shovon Pal},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2606.25381},
eprint = {2606.25381},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.25381},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Spectroscopic signatures of Kohn anomaly in a topological crystalline insulator
AU - Jingwen Li
AU - Arpita Dutta
AU - Kush Saha
AU - Andrzej Szczerbakow
AU - Tomasz Story
AU - Manfred Fiebig
AU - Shovon Pal
PY - 2026
DA - 2026/09/16
PB - arXiv
DO - 10.48550/arxiv.2606.25381
UR - https://arxiv.org/abs/2606.25381
AB - Topological crystalline insulators extend the concept of topological insulators by hosting surface states protected by crystallographic symmetry. Their topological phase transitions arise from spin-orbit-driven band inversion in the bulk electronic structure, reshaping the low-energy electronic environment and its coupling to lattice excitations. While the electronic aspects of band topology are well established, the corresponding dynamics of lattice and electron-phonon interactions remain largely unexplored. Here, we report a pronounced softening of a low-energy surface phonon mode across the topological phase transition in Pb_0.77Sn_0.23Se, revealed by temperature-dependent time-domain terahertz spectroscopy. Unlike the well-known phonon softening in ferroelectrics, this effect does not signal a structural instability but instead reflects electronic reconstruction. We attribute the softening to the spectroscopic manifestations of a Kohn anomaly, indicating a strong coupling between lattice vibrations and Dirac-like surface electrons in the topological phase. Consistently, the phonon linewidth deviates from the standard anharmonic temperature dependence, further evidencing enhanced electron-phonon coupling. The observed changes in phonon frequency and linewidth at around 120 K are consistent with the reported topological phase transition temperature in this material. Our results thus provide a spectroscopic route for the distinct identification of the onset of a topological phase.
ER -