Dynamical properties of the magnetic topological insulator <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>T</mml:mi><mml:msub><mml:mi>Bi</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Te</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow><mml:mo> </mml:mo><mml:mo>(</mml:mo><mml:mi>T</mml:mi><mml:mo>=</mml:mo><mml:mi>Mn</mml:mi><mml:mo>,</mml:mo><mml:mi>Fe</mml:mi><mml:mo>)</mml:mo></mml:math>: Phonons dispersion, Raman active modes, and chiral phonons study
Aksel Kobiałka, M. Sternik, Andrzej Ptok
Abstract
Recently discovered magnetic topological insulators $T{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4} (T=\mathrm{Mn},\mathrm{Fe})$ crystallize into the $R\overline{3}m$ rhombohedral structure and exhibit the antiferromagnetic order. Here, we discuss the lattice dynamics of these compounds to confirm the stability of these systems. We show that the phonon dispersion does not contain soft modes, so both compounds are dynamically stable in the $R\overline{3}m$ phase. We perform theoretical analyses of the mode activity at the $\mathrm{\ensuremath{\Gamma}}$ point for the discussed compounds. In the case of the Raman active modes, our results are in agreement with the experimentally observed frequencies. Finally, we also discuss the possibility of the realization of chiral phonons.