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 two-dimensional (2D)
van der Waals (vdW) materials. Herein, we report the observation of spin-phonon
coupling in the otherwise non-magnetic TI Bi2βTe3β, due
to the proximity of FePS3β (an antiferromagnet (AFM), TNββΌ 120 K), in a vdW heterostructure framework. Temperature-dependent Raman
spectroscopic studies reveal deviation from the usual phonon anharmonicity
at/below 60 K in the peak position (self-energy) and linewidth (lifetime) of
the characteristic phonon modes of Bi2βTe3β (106 cmβ1 and 138
cmβ1) in the stacked heterostructure. The Ginzburg-Landau (GL) formalism,
where the respective phonon frequencies of Bi2βTe3β couple to phonons
of similar frequencies of FePS3β in the AFM phase, has been adopted to
understand the origin of the hybrid magneto-elastic modes. At the same time,
the reduction of characteristic TNβ of FePS3β 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, our data
suggest a double softening of phonon modes of Bi2βTe3β
(at 30 K and 60 K), which in turn, demonstrates Raman scattering as a possible
probe for delineating the magnetic ordering in bulk and surface of a hybrid
topological insulator