Anomalous behavior of the $E_u^1$ infrared-active phonon mode in a Bi$_{2-x}$Sr$_x$Se$_3$ crystal

A. A. Melnikov; K. N. Boldyrev; Yu. G. Selivanov; S. V. Chekalin

doi:10.1134/S0021364022010039

paper

Anomalous behavior of the $E_{u}^{1}$ infrared-active phonon mode in a Bi $_{2 - x}$ Sr $_{x}$ Se $_{3}$ crystal

arXiv:2201.06528 · doi:10.1134/S0021364022010039

Abstract

We have studied spectral evolution of the $E_{u}^{1}$ phonon line of a topological insulator Bi $_{2 - x}$ Sr $_{x}$ Se $_{3}$ with temperature. Unlike the Raman-active phonons, the $E_{u}^{1}$ mode demonstrates softening upon cooling the crystal, and the corresponding spectral line acquires a pronounced Fano-like shape at temperatures $T ≲ 100$ K. We interpret the latter effect as a signature of specific coupling of the bulk infrared active phonons to surface Dirac electrons. Using coherent resonant excitation of the $E_{u}^{1}$ mode as a surface sensitive tool, we have detected softening of the surface counterpart of the bulk $E_{u}^{1}$ phonon mode upon strontium doping. This observation can be an evidence of enhanced electron-phonon interaction at the surface of the Bi $_{2 - x}$ Sr $_{x}$ Se $_{3}$ crystal.

6 pages, 4 figures

Anomalous behavior of the Eu1​ infrared-active phonon mode in a Bi2−x​Srx​Se3​ crystal

Abstract

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Anomalous behavior of the $E_{u}^{1}$ infrared-active phonon mode in a Bi $_{2 - x}$ Sr $_{x}$ Se $_{3}$ crystal