Terahertz Electric Field Driven Electric Currents and Ratchet Effects in Graphene

Abstract

Terahertz field induced photocurrents in graphene were studied experimentally and by microscopic modeling. Currents were generated by cw and pulsed laser radiation in large area as well as small-size exfoliated graphene samples. We review general symmetry considerations leading to photocurrents depending on linear and circular polarized radiation and then present a number of situations where photocurrents were detected. Starting with the photon drag effect under oblique incidence, we proceed to the photogalvanic effect enhancement in the reststrahlen band of SiC and edge-generated currents in graphene. Ratchet effects were considered for in-plane magnetic fields and a structure inversion asymmetry as well as ratchets by non-symmetric patterned top gates. Lastly, we demonstrate that graphene can be used as a fast, broadband detector of terahertz radiation.

Giant ratchet magneto-photocurrent in graphene lateral superlattices

“…[11][12][13][14]. In graphene, the ratchet effect can be obtained in monolayers with asymmetric micropatterns [15][16][17], layers with built-in structure inversion asymmetry [18] (in this case it is typically called photogalvanic effect [11]), short-channel devices, like field effect transistors with asymmetric boundary conditions [1,[19][20][21][22][23][24][25], as well as in structures with asymmetric grating type of electrodes [26][27][28][29][30][31]. Besides their fundamental significance, the two latter types of ratchets are extremely important for applications, since they provide a very promising route towards fast, sensitive, and gate-tunable detection of THz radiation at room temperature.…”

Light-field and spin-orbit-driven currents in van der Waals materials

“…For the latter, the transfer of momentum from photons to electron drives the electric current. The photon drag effect shows a qualitatively similar polarization dependence as the photogalvanic effect, but a distinctly different dependence on photon momentum q [86,[113][114][115].…”

Rectification of AC Electric Current at the Edge of 2D Electron Gas

“…Such a geometry excludes the generation of bulk DC electric currents due to the photon drag or photogalvanic effects which would emerge at oblique incidence of radiation. [ 2,9,22 ] The electric field causes back and forth motion of electrons which is distorted at the edge. Such a distortion of electron transport near the edge leads, in the second order in the electric field amplitudes, to a DC electric current (see Figure 1).…”

“…Such phenomena, referred to as the electronic ratchets or the photogalvanic effects for the optical range of high‐frequency electric fields, occur in systems with broken space inversion symmetry (parity inversion or P ‐symmetry). [ 1 ] They are being widely studied in 2D conducting systems based on semiconductor quantum wells, [ 2–7 ] graphene [ 8,9 ] and graphene bilayers, [ 10,11 ] transition metal dichalcogenides, [ 12,13 ] and so on. The studied systems lack the space inversion symmetry, which enables the generation of electric currents in the 2D plane.…”