Phonon modes and Raman signatures of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Mn</mml:mi><mml:msub><mml:mi>Bi</mml:mi><mml:mrow><mml:mn>2</mml:mn><mml:mi>n</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>Te</mml:mi><mml:mrow><mml:mn>3</mml:mn><mml:mi>n</mml:mi><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mi>n</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mn>2</mml:mn><mml:mo>,</mml:mo><mml:mn>3</mml:mn><mml:mo>,</mml:mo><mml:mn>4</mml:mn></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math> magnetic topological heterostructures
Yujin Cho, Jin Ho Kang, Liangbo Liang, M.G Jeremy Taylor, Xiangru Kong, Subhajit Ghosh, Fariborz Kargar, Chaowei Hu, Alexander A. Balandin, Alexander A. Puretzky, Ni Ni, Chee Wei Wong
Abstract
An intrinsic antiferromagnetic topological insulator ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ arises when intercalating a Mn-Te bilayer chain in a topological insulator, ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. We present observations on the inter- and intralayer phonon modes of the generalized $\mathrm{Mn}\phantom{\rule{0.28em}{0ex}}{\mathrm{Bi}}_{2n}{\mathrm{Te}}_{3n+1}(n=1,2,3,4)$ family using cryogenic low-frequency Raman spectroscopy with various polarization configurations. Two peaks at 66 and $112\phantom{\rule{0.28em}{0ex}}\mathrm{c}{\mathrm{m}}^{\text{--}1}$ show abnormal perturbation in Raman linewidths below magnetic transition temperature due to spin-phonon coupling. In ${\mathrm{MnBi}}_{4}{\mathrm{Te}}_{7}$, ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ layers induce Davydov splitting of the ${A}_{1g}$ mode around $137\phantom{\rule{0.28em}{0ex}}\mathrm{c}{\mathrm{m}}^{\text{--}1}$ at 5 K. The out-of-plane interlayer force constant estimated using the linear chain model was $(3.98\ifmmode\pm\else\textpm\fi{}0.14)\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{0.28em}{0ex}}\mathrm{N}/{\mathrm{m}}^{3}$, three times weaker than that of ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. Adding more ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ layers, such as ${\mathrm{MnBi}}_{6}{\mathrm{Te}}_{10}$ and ${\mathrm{MnBi}}_{8}{\mathrm{Te}}_{13}$, makes ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ properties more dominant than magnetic properties. Our work experimentally and theoretically discovers the dynamics of phonon modes of $\mathrm{Mn}\phantom{\rule{0.16em}{0ex}}{\mathrm{Bi}}_{2n}{\mathrm{Te}}_{3n+1}$ family, facilitating utilization of magnetic topological heterostructures.