(n=1,2,3,4) topological heterostructures*

MnBi₂Te₄ is the first experimentally demonstrated intrinsic antiferromagnetic topological insulator, whose properties are tunable with additional Bi₂Te₃ layers between adjacent MnBi₂Te₄ layers. In this talk, we present the phonon modes of bulk MnBi_2nTe_3n+1 (n=1,2,3,4) at various temperatures and polarization configurations, using optical Raman spectroscopy. Our density functional theory calculation shows that the peaks at 66 cm^-1 and 112 cm^-1 are mainly generated by oscillating Mn-Te chains. In MnTe₂Te₄, below the transition temperature, we observed an abnormal change of those two peaks due to spin-phonon coupling. In MnBi₄Te₇, the additional Bi₂Te₃ induces Davydov splitting of the A_1g mode at 136 cm^-1 at room temperature. From the linear chain model, we estimated the out-of-plane interlayer force constant to be 4.48×10¹⁹ N/m³, 75% weaker than that of Bi₂Te₃. As the number of Bi₂Te₃ layer increases, the Raman spectrum is dominated by the vibrational modes in Bi₂Te₃. Our work provides useful guidance to tailoring their physical properties in future research.