Strain-controlled spin and charge pumping in graphene devices via spin-orbit coupled barriers

Abstract

-We theoretically propose a graphene-based adiabatic quantum pump with intrinsic spin-orbit coupling (SOC) subject to strain where two time-dependent extrinsic spin-orbit coupled barriers drive spin and charge currents. We study three differing operation modes where i) location, ii) chemical potential, and iii) SOC of the two barriers oscillate periodically and out of phase around their equilibrium states. Our results demonstrate that the amplitude of adiabatically pumped currents highly depends on the considered operation mode. We find that such a device operates with highest efficiency and in a broader range of parameters where the barriers' chemical potential drives the quantum pump. Our results also reveal that by introducing strain to the system, one can suppress or enhance the charge and spin currents separately, depending on strain direction.Spintronics is an emerging filed which has aimed at exploiting the spin degree of freedom to construct faster and high performance low-power nanoscale devices [1]. The discovery of isolated graphene monolayer [2,3], a single layer of Carbon atoms, with unique electrical, optical and thermal properties has triggered numerous efforts to achieve graphene-based nanoscale devices [5][6][7][8]. The massless Dirac fermions in ballistic graphene can reflect chirality and linear dispersion relation of graphene around the Dirac points; two inequivalent corners of the first Brillouin zone [4]. Also, the long spin relaxation time of the Dirac fermions in graphene monolayers due to a small intrinsic spin-orbit coupling (SOC) which originates from the intra-atomic spin-orbit coupling of the Carbon atoms has made it an exceptional candidate to the spintronics devices [7].Quite recently, it was experimentally demonstrated that a strong Rashba SOC ∼ 17 meV can be induced into graphene monolayers by means of proximity to a semiconducting tungsten disulphide substrate [8]. This finding is highly appealing in terms of generation and manipulation of spin currents in more controllable platforms. The intrinsic SOC that can be caused by the crystalline potential associated with the band structure respects all the lattice symmetries in graphene and results in a small energy gap at the Dirac points. The extrinsic or Rashba SOC, however, results from the lack of inversion symmetry due to perpendicular electric fields, substrate effects, chemical doping, or curvature of graphene corrugations and can be responsible for inducing a spin polarization in graphene. [9,10] The influences of intrinsic and Rashba SOCs on the transport properties of graphene monolayer systems have extensively been studied in the recent years [5,6,[11][12][13][14]. For instance, it was shown that spin polarization induced by a charge current can reside in the graphene plane and perpendicular to the electric field while its sign changes by varying the Fermi level through an external gate voltage [11]. Also, it was theoretically found that the interplay of massive electrons with SOC or strain in a graphene layer can...

Tunable anomalous Andreev reflection and triplet pairings in spin-orbit-coupled graphene

“…For example, the interplay of massive electrons with spin orbit coupling in the presence of strain in a graphene layer yields controllable spatially separated spin-valley filtering 38,39 . Therefore, this property can be employed as a means to control the spin-transport graphene-based spintronics devices 46 .…”

Boundary conditions and Green function approach of the spin–orbit interaction in the graphitic nanocone

“…In Fig. 12, we see that (30) will coincide with the left part of Fig. 11 much better for the case N = 1/20.…”

“…These results promise practical applications of the graphitic nanocones in close future. New calculations related to the spin-orbital coupling in graphene [30] as well as the theoretical and experimental investigations of graphene monolayer and bilayer from the last days [31,32] contribute to this goal.…”

Numerical simulation of quantized current generated by a quantum dot pump

“…[8][9][10][11][12] Also, spin pumping in graphene devices [13][14][15][16][17][18] and adiabatic pumping [19][20][21] were studied recently. It has been reported that the quantized current pumping can be achieved by applying periodic voltage modulation on a quantum dot gate.…”