Large room-temperature anisotropic magneto-photothermal voltage in Sb2Te3 topological insulator thin films

We report a large, room-temperature anisotropic magneto-photothermal voltage in granular, c axis oriented Sb2Te3 topological insulator thin films generated by focused laser illumination without an external electrical bias. By rotating an external magnetic field in three orthogonal planes, three distinct contributions to the photovoltage are resolved: an ordinary Nernst response arising from out-of-plane thermal gradients, a previously unreported planar anisotropic magneto-thermal contribution associated with in-plane temperature gradients, and a field-angle-independent offset component. Spatial line scans across the device further separate the nearly uniform out-of-plane Nernst contribution from the antisymmetric spatial variation of the in-plane thermoelectric contribution. Systematic thickness-dependent measurements show that the normalized anisotropic planar photothermal response remains nearly unchanged, with only a weak decrease with increasing thickness. This weak thickness dependence is inconsistent with a conventional mobility-dependent anisotropic thermoelectric response and supports an intrinsic contribution from the nontrivial bulk electronic states that is relatively insensitive to grain-boundary scattering. These findings establish a prominent anisotropic magneto-photothermal paradigm in topological insulator thin films, providing a robust, all-optical scheme for room-temperature thermoelectric and optoelectronic applications.