Pure spin current injection in hydrogenated graphene structures

Abstract

We present a theoretical study of spin-velocity injection (SVI) of a pure spin current (PSC) induced by a linearly polarized light that impinges normally on the surface of two 50% hydrogenated noncentrosymmetric two-dimensional (2D) graphene structures. The first structure, hydrogenated at only one side, labeled Up, also known as graphone, and the second, labelled Alt, is 25% hydrogenated at both sides. The hydrogenation opens an energy gap in both structures. We analyze two possibilities: in the first, the spin is fixed along a chosen direction, and the resulting SVI is calculated; in the second, we choose the SVI direction along the surface plane, and calculate the resulting spin orientation. This is done by changing the energyhω and polarization angle α of the incoming light. The results are calculated within a full electronic band structure scheme using the Density Functional Theory (DFT) in the Local Density Approximation (LDA). The maxima of the spin-velocities are reached whenhω = 0.084 eV and α = 35 • for the Up structure, and hω = 0.720 eV and α = 150 • for the Alt geometry. We find a speed of 668 Km/s and 645 Km/s for the Up and the Alt structures, respectively, when the spin points perpendicularly to the surface.Also, the response is maximized by fixing the spin-velocity direction along a high symmetry axis, obtaining a speed of 688Km/s with the spin pointing at 13 • from the surface normal, for the Up, and 906 Km/s and the spin pointing at 60 • from the surface normal, for the Alt system. These speed values are of order of magnitude larger than those of bulk semiconductors, such as CdSe and GaAs, thus making the hydrogenated graphene structures excellent candidates for spintronics applications. PACS numbers: 75.76+j,85.75.-d,78.67.Wj,78.90.+t arXiv:1709.02282v1 [cond-mat.mes-hall]

Surface functionalization of the honeycomb structure of zinc antimonide (ZnSb) monolayer: A first-Principles study

“…The theoretical predictions and experimental observations revealed that electronic properties of graphene can be tuned via either one or two types of surface modifications. [40][41][42][43] In addition, fluorination has been shown to be also an efficient way for tuning the structural, magnetic, electronic, and mechanical properties of 2DMs. [44][45][46][47][48][49][50] In addition to freestanding stable 2DMs, the 2D forms of non-layered bulk materials offer a rich variety of advantages for their surface functionalization due to the unsaturated surface orbitals.…”

Pure spin current injection of single-layer monochalcogenides

“…x,y (ω), which is the central result of this article, has a rich structure as a function of hω, and more importantly, reaches values around ±100 Km/s, albeit not necessarily at the same energies; similar values of the SVI were predicted for hydrogenated graphene. 8 Right at the energy gap, we see the onset of µ azbc (ω) and ξ aa (ω), and correspondingly of v z…”

“…[1][2][3][4] Pure spin current (PSC), i.e., spin current with no associated charge current, could lead to more efficient quantum devices because a PSC does not produce joule heating. A PSC can be realized in the spin Hall effect, 5 one photon absorption of light, [6][7][8] or interference of two optical beams. 9,10 In contrast to the well-known spin Hall effect which occurs in the ground state of the material, optically induced PSC occurs in excited states of the material.…”

Bulk photospin effect

“…At very short times, interband coherence of conduction bands plays an important role in insulators that break IS. 14,[44][45][46][47] Here we recover the equations describing this effect starting from Eq. (42).…”