Abstract
We report on the observation of the magnetic quantum ratchet effect in graphene with a lateral dual-grating top gate (DGG) superlattice. We show that the THz ratchet current exhibits sign-alternating magneto-oscillations due to the Shubnikov-de Haas effect. The amplitude of these oscillations is greatly enhanced as compared to the ratchet effect at zero magnetic field. The direction of the current is determined by the lateral asymmetry which can be controlled by variation of gate potentials in DGG. We also study the dependence of the ratchet current on the orientation of the terahertz electric field (for linear polarization) and on the radiation helicity (for circular polarization). Notably, in the latter case, switching from right- to left-circularly polarized radiation results in an inversion of the photocurrent direction. We demonstrate that most of our observations can be well fitted by the drift-diffusion approximation based on the Boltzmann kinetic equation with the Landau quantization fully encoded in the oscillations of the density of states.
Highlights
The discovery of graphene opened a new research direction in condensed matter physics
In our previous work [29], in which we studied similar structures and applying terahertz radiation with the same parameters, we demonstrated that illumination of the dual-grating top gate (DGG) superlattice on graphene results in a photocurrent exhibiting characteristic behavior of the ratchet effect
Photocurrent direction and magnitude: (i) are sensitive to the orientation of the radiation electric field vector E and/or the radiation helicity, (ii) depend on the carrier charge sign, and (iii) are controlled by the lateral asymmetry parameter, which can be varied by applying voltages UTG1 and UTG2 to the individual subgates
Summary
The discovery of graphene opened a new research direction in condensed matter physics. The unique optical properties of this material prompted a rapid development of photonics and optoelectronics. These are especially important for applications in the terahertz (THz) range of frequencies; see e.g., Refs. THz-radiation-induced nonlinear optical effects, including rectification of THz/infrared electromagnetic waves, offer a new playground for many intriguingphenomena in graphene; see, e.g., reviews [9,10]. These phenomena deliver graphene-specific mechanisms of photocurrent generation and provide a basis for the development of novel graphene radiation plasmonic detectors. Tunable by gate voltage and have already shown fast and sensitive operation in a broad frequency band from sub-THz to infrared, and from ambient- to cryogenic temperatures
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