Circular ratchet currents in two dimensional tellurene with an asymmetric grating

Abstract

Abstract Terahertz ratchet effect converts alternating electric fields into direct currents in low-dimensional systems with broken spatial symmetry and provide a route towards room-temperature terahertz optoelectronics. Here, we investigate the ratchet effect in two-dimensional tellurene, whose crystal structure is formed by helical atomic chains and exhibits intrinsic chirality. Terahertz excitation generates a circular ratchet photocurrent flowing along the chiral c axis, whose direction is controlled by the radiation helicity and reverses when the radiation helicity is switched from right- to left-handed circular polarization. The photocurrent is observed at room temperature over a broad range of gate voltages, with the Fermi level tuned from the conduction band near the Weyl point through the band gap and into the valence band, where the energy dispersion is nearly parabolic. A microscopic theory based on the Boltzmann kinetic equation reproduces the polarization and gate-voltage dependences of the photocurrent. Our results highlight a potential of tellurene based ratchet devices for helicity-sensitive terahertz photodetection.