Optical properties of van der Waals heterostructure of uniaxially strained graphene on TMD

Abstract

The spin and valley polarizations and plasmonics in Van der Waals heterostructures of strained graphene monolayer on 2D transition metal dichalcogenide (GrTMD) substrate are reported in this communication. The substrate induced interactions (SII) involve sub-lattice-resolved, and enhanced intrinsic spin-orbit couplings, the extrinsic Rashba spin-orbit coupling (RSOC), and the orbital gap related to the transfer of the electronic charge from graphene to the substrate. Furthermore, magnetic impurity atoms are deposited to the graphene surface and the corresponding exchange field is included in the band dispersion. A Rashba coupling dependent pseudo Zeeman term arising due to the interplay of SIIs was found to be responsible for the spin degeneracy lifting and the spin polarization. The latter turns out to be electrostatic doping and the exchange field tunable and inversely proportional to the square root of the carrier concentration. The strain field, on the other hand, brings about the valley polarization. The intra-band plasmon dispersion for the finite doping and the long wavelength limit has also been obtained. The dispersion involves the q2/3 behavior and not the well known q1/2 behavior. The uniform, uniaxial strain does not bring about any change in this behavior. However, the plasmon dispersion gets steeper for the wavevector perpendicular to the direction of strain and is flattened for wave vectors along the direction of the strain with the term responsible for the flattening proportional to the strain field. The stronger confinement capability of GrTMD Plasmon compared to that of standalone, doped graphene is an important outcome of the present work. One finds that whereas the intra-band absorbance of GrTMD is decreasing function of the frequency at a given strain field, it is an increasing function of the strain field at a given frequency.