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Optical control of helicity-dependent photocurrent in topological insulatorSb$_2$Te$_2$Se has been studied at room temperature on dominantly c-axisoriented granular polycrystalline samples grown by pulsed laser depositiontechnique. Strong spin-orbit coupling and spin-momentum locking make thissystem unique for their applications. We observed that photocurrent can becontrolled by exciting the sample with different circular and linear polarizedlight, yielding a polarization-dependent current density which can be fittedvery well with a theoretical model. Magnitude of the photocurrent is highereven at room temperature, compared to previous reports on other single-crystaltopological insulators. Comparison with the theoretical model suggests thatphotocurrent has different contributions. Study of dependence of photocurrenton the angle of incidence (wave-vector) of the excitation laser beam withrespect to the surface normal of the sample helps to identify origins ofdifferent terms contributing to the observed photocurrent. Incidence-angledriven helicity switching, which is a very simple and effective technique tocontrol the directional photocurrent, has also been observed in this study.This photocurrent can also be controlled with the help of photothermal gradientgenerated by the excitation light beam. Enhancement and inversion of thisphotocurrent in presence of photothermal gradient for light incident on twoopposite edges of the sample occur due to selective spin state excitation withtwo opposite (left and right) circularly polarized light in presence of theunique spin-momentum locked surface states. These observations renders thispolycrystalline material to be more important in polarization-dependentphotodetection applications as well as for spin-optoelectronics under ambientconditions.

Controlling helicity-dependent photocurrent in polycrystalline  Sb$_2$Te$_2$Se topological insulator thin films at ambient temperature  through wave-vector of and photothermal gradient due to polarized light