  We studied longitudinal and Hall photothermal voltages under a planar
magnetic field scan in epitaxial thin films of the Topological Insulator (TI)
Sb2Te3, grown using pulsed laser deposition (PLD). Unlike prior research that
utilised polarised light-induced photocurrent to investigate the TI, our study
introduces advancements based on unpolarized light-induced local heating. This
method yields a thermoelectric response exhibiting a direct signature of strong
spin-orbit coupling. Our analysis reveals three distinct contributions when
fitting the photothermal voltage data to the angular dependence of the planar
magnetic field. The interaction between the applied magnetic field and the
thermal gradient on the bulk band orbitals enables the differentiation between
the ordinary Nernst effect from the out-of-plane thermal gradient and an
extraordinary magneto-thermal contribution from the planar thermal gradient.
The fitting of our data to theoretical models indicates that these effects
primarily arise from the bulk states of the TI rather than the surface states.
These findings highlight PLD-grown epitaxial topological insulator thin films
as promising candidates for optoelectronic devices, including sensors and
actuators. Such devices offer controllable responses through
position-dependent, non-invasive local heating via focused incident light and
variations in the applied magnetic field direction.
