Abstract
We theoretically study the electronic and transport properties of two graphene layers vertically coupled by an insulating layer under the influence of a time-periodic external light field. The non-adiabatic driving induces excitations of electrons and a redistribution of the occupied states which is manifested in the opening of gaps in the quasienergy spectrum of graphene. When a voltage is applied between the top and bottom graphene layers, the photo-induced nonequilibrium occupation modifies the transport properties of the contact. We investigate the electronic and transport properties of the contact by using the nonequilibrium Green's function formalism. To illustrate the behavior of the differential conductance of the vertical contact under the light illumination, we consider two cases. First, we assume that both the bottom and top layers consist of graphene and second we consider a finite mass term in the bottom layer. We obtain that the differential conductance is strongly suppressed due to the opening of gaps in the quasienergy spectrum in graphene. Additionally, the conductance shows features corresponding to the tunneling of photoexcited electrons at energies of the van Hove singularity for both the top and bottom layers. In the case of a finite mass term in the bottom layer, the differential conductance can be directly related to the tunneling of photoexcited electrons.
Highlights
The outstanding mechanical, optical, and electronic properties of graphene make it an attractive material for nextgeneration technology [1]
Motivated by the growing interest in nonequilibrium driving of graphene devices, we study a contact consisting of two graphene layers vertically separated by an insulating layer
Motivated by the fact that an underlying substrate [71] or Coulomb interaction [60] opens a gap in the band structure of graphene, we discuss two scenarios: (i) we assume that both the top and the bottom layers consist of graphene. (ii) We discuss the case that the top layer consists of graphene and the bottom layer consists of graphene with a finite mass term opening a gap in the band structure
Summary
The outstanding mechanical, optical, and electronic properties of graphene make it an attractive material for nextgeneration technology [1]. Apart from employing light-matter interaction in graphene to enhance the functionality of optoelectronic devices, graphene reveals several fundamental light-induced phenomena [16] One of these phenomena is the possibility to open gaps in the energy spectra by irradiating graphene with a timeperiodic potential [17,18,19,20,21,22,23,24]. Various aspects of the suppression of the conductance due to light-matter interaction have been discussed in Refs. Similar to the top layer, we introduce the Hamiltonian of the bottom layer and the tunneling Hamiltonian
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