Manipulating Spin–Lattice Coupling in Layered Magnetic Topological Insulator Heterostructure via Interface Engineering

Induced magnetic order in a topological insulator (TI) can be realized either by depositing magnetic adatoms on the surface of a TI or engineering the interface with epitaxial thin film or stacked assembly of 2D van der Waals (vdW) materials. Herein, the observation of spin-phonon coupling in the otherwise non-magnetic TI Bi₂Te₃ is reported, due to the proximity of FePS₃ (an antiferromagnet (AFM), T_N ≈ 120 K), in a vdW heterostructure framework. Temperature-dependent Raman spectroscopic studies reveal deviation from the usual phonon anharmonicity originated from spin-lattice coupling at the Bi₂Te₃/FePS₃ interface at/below 60 K in the peak position (self-energy) and linewidth (lifetime) of the characteristic phonon modes of Bi₂Te₃ (106 and 138 cm^–1) in the stacked heterostructure. The Ginzburg-Landau (GL) formalism, where the respective phonon frequencies of Bi₂Te₃ couple to phonons of similar frequencies of FePS₃ in the AFM phase, is adopted to understand the origin of the hybrid magneto-elastic modes. At the same time, the reduction of characteristic TN of FePS₃ from 120 K in isolated flakes to 65 K in the heterostructure, possibly due to the interfacial strain, which leads to smaller Fe-S-Fe bond angles as corroborated by computational studies using density functional theory (DFT). Besides, inserting hexagonal boron nitride within Bi₂Te₃/FePS₃ stacking regains the anharmonicity in Bi₂Te₃. As a result, controlling interfacial spin-phonon coupling in stacked heterostructure can have potential application in surface code spin logic devices.. Authors: Maity, Sujan [Indian Association for the Cultivation of Science, Kolkata (India); University of Central Florida]; Dey, Dibyendu [University of Maine, Orono, ME (United States); University of Central Florida, Orlando, FL (United States)]; Ghosh, Anudeepa [Indian Association for the Cultivation of Science, Kolkata (India)]; Masanta, Suvadip [Bose Institute, Kolkata (India)] (ORCID:0009000073814409); De, Binoy Krishna [UGC-DAE Consortium for Scientific Research Indore Centre, Indore (India)]. DOE Contract: SC0021127. Subjects: 36 MATERIALS SCIENCE