2021/07/07 by Yujin Cho, Jin Ho Kang, Cho, Yujin +18 · 2 citations
Physics and Astronomy · Earth and Planetary Sciences · #Topological Materials and Phenomena #Physics of Superconductivity and Magnetism #High-pressure geophysics and materials
paper · pdf · doi:10.48550/arxiv.2107.03204
An intrinsic antiferromagnetic topological insulator MnBi2Te4 can be realized by intercalating Mn-Te bilayer chain in a topological insulator, Bi2Te3. MnBi2Te4 provides not only a stable platform to demonstrate exotic physical phenomena, but also easy tunability of the physical properties. For example, inserting more Bi2Te3 layers in between two adjacent MnBi2Te4 weakens the interlayer magnetic interactions between the MnBi2Te4 layers. Here we present the first observations on the inter- and intra-layer phonon modes of \mathrmMnBi2nTe3n+1 (n=1,2,3,4) using cryogenic low-frequency Raman spectroscopy. We experimentally and theoretically distinguish the Raman vibrational modes using various polarization configurations. The two peaks at 66 cm-1 and 112 cm-1 show an abnormal perturbation in the Raman linewidths below the magnetic transition temperature due to spin-phonon coupling. In MnBi4Te7, the Bi2Te3 layers induce Davydov splitting of the A1g mode around 137 cm-1 at 5 K. Using the linear chain model, we estimate the out-of-plane interlayer force constant to be (3.98 ± 0.14) × 1019 N/m3 at 5 K, three times weaker than that of Bi2Te3. Our work discovers the dynamics of phonon modes of the MnBi2Te4 and the effect of the additional Bi2Te3 layers, providing the first-principles guidance to tailor the physical properties of layered heterostructures.