Optical control of spin-polarized photocurrent in topological insulator thin films

Abstract

Dirac electrons in topological insulators (TIs) provide one possible avenue to achieve control of photocurrents and spin currents without the need to apply external fields by utilizing characteristic spin-momentum locking. However, for TI crystals with electrodes it is actually difficult to characterize the net flow of spin-polarized photocurrents because of the coexistence of surface carriers and bulk carriers generated by optical excitations. We demonstrate here that the net flow directions of spin-polarized photocurrents in TI polycrystalline thin films without electrodes can be precisely and intentionally controlled by the polarization of the excitation pulse alone, which is characterized by performing time-domain terahertz (THz) wave measurements and time-resolved magneto-optical Kerr rotation measurements that are non-contact methods. We show that the amplitudes of s-polarized THz waves radiated from photocurrents under right- and left-circularly polarized excitations are inverted relative to one another. Moreover, we observe the inversion of time-resolved magneto-optical Kerr rotation signals between the two excitations. Our results will open the way as innovative methods to control spin-polarized electrons in optoelectronic and spintronic TI devices without the need to apply external fields.

A light-induced phononic symmetry switch and giant dissipationless topological photocurrent in ZrTe5

“…For nonlinear photocurrent generation, we use THz emission spectroscopy to measure E s (Fig. 1b) directly in the time-domain [19][20][21][22][23][24] , where the THz amplitude is determined by the size of the photocurrent and the bandwidth by photocurrent relaxation. E s directly relates to the nonlinear photocurrents J THz by (see Methods)…”

Deep tuning of photo-thermoelectricity in topological surface states

“…The coefficient C of sin2α represents the helical current of TSS. The TSS origin of the helicity-dependent photocurrent has been confirmed in tetradymite TIs via carrier modulation 37,39 and ultrafast dynamics 44,45 . The sin4α and cos4α terms represent the current due to linear polarization rotation associated with QWP rotation, originated from the linear photogalvanic or photon drag effect 46,47 .…”

Photocurrent response in parity-time symmetric current-ordered states

“…The photo-induced electric current is detected through the contact conductivity measurement or by measuring the terahertz lights radiating from flowing photocurrent. In particular, the terahertz-light detection of the photocurrent is less sensitive to photo-thermal effects [57,58] and is conveniently distinguished from other contributions such as the spin-galvanic effect [57,[59][60][61].…”