Gate-dependent spin Hall induced nonlocal resistance and the symmetry of spin-orbit scattering in Au-clustered graphene

Abstract

Engineering the electron dispersion of graphene to be spin-dependent is crucial for the realization of spin-based logic devices. Enhancing spin-orbit coupling in graphene can induce spin Hall effect, which can be adapted to generate or detect a spin current without a ferromagnet. Recently, both chemically and physically decorated graphenes have shown to exhibit large nonlocal resistance via the spin Hall and its inverse effects. However, these nonlocal transport results have raised critical debates due to the absence of field dependent Hanle curve in subsequent studies. Here, we introduce Au clusters on graphene to enhance spin-orbit coupling and employ a nonlocal geometry to study the spin Hall induced nonlocal resistance. Our results show that the nonlocal resistance highly depends on the applied gate voltage due to various current channels. However, the spin Hall induced nonlocal resistance becomes dominant at a particular carrier concentration, which is further confirmed through Hanle curves. The obtained spin Hall angle is as high as ∼0.09 at 2 K. Temperature dependence of spin relaxation time is governed by the symmetry of spin-orbit coupling, which also depends on the gate voltage: asymmetric near the charge neutral point and symmetric at high carrier concentration. These results inspire an effective method for generating spin currents in graphene and provide important insights for the spin Hall effect as well as the symmetry of spin scattering in physically decorated graphene.

Local equilibrium charge and spin currents in two-dimensional topological systems

“…Only by taking into account all terminal injections one obtains correct results. The pictures usually drawn in experimental studies of spin and valley Hall effects [63][64][65][66][67][68][69][70] can be misleading as they indicate that the electrons injected from the source terminal flow to neighboring terminals (depending on the spin or the valley degree of freedom) other than the drain terminal. This would imply breaking of charge conservation.…”

Observation of spin-polarized Anderson state around charge neutral point in graphene with Fe-clusters

“…Synthesis and transfer of graphene. A monolayer graphene was grown on a polycrystalline Cu foil using a chemical vapor deposition method demonstrated elsewhere 23 . 25 μm copper foil (Alfa Aesar, 99.8% purity) was electropolished in phosphoric acid for 15 min and rinsed with distilled water followed by isopropyl alcohol (IPA).…”

“…Electron band structure of pristine graphene has been extensively studied over the last decade because of its unusual transport properties 8,9 , and it has been shown that physical properties of graphene can be strongly modified when it is functionalized with various adatoms [10][11][12][13][14][15][16][17][18][19][20][21][22][23] , or proximity effect from heterostructures [24][25][26][27][28][29][30] . Disordered graphene by heavy adatoms could exhibit diverse condensed matter phenomena such as spin Hall effect and QSH state (topological insulator state) due to the instilled spin-orbit coupling and honeycomb lattice distortion.…”

“…Disordered graphene by heavy adatoms could exhibit diverse condensed matter phenomena such as spin Hall effect and QSH state (topological insulator state) due to the instilled spin-orbit coupling and honeycomb lattice distortion. For example, chemically or physically decorated adatom in graphene could exhibit spin-charge conversion known as spin Hall effect due to induced strong spin-orbit coupling [21][22][23] . Also, it was theoretically predicted that dilute heavy adatoms, such as platinum, indium and thallium, could lead to a robust QSH state in graphene, with a band gap exceeding that of pure graphene by many orders of magnitude 14 .…”

Ambipolar charge transport in quasi-free-standing monolayer graphene on SiC obtained by gold intercalation

“…Among all intercalants, Au has shown the possibility to result in n-type or p-type doped graphene depending on the amount of gold that is intercalated [14,15]. In addition to controlling the doping type, Au is attractive because it could lead to enhancing spin-orbit interaction (SOI) in graphene, which holds promises for a variety of spin-related phenomena in graphene [16][17][18][19]. From a practical point of view, the chemical inertness of Au is also attractive, because it can enable the ex situ processing of intercalated graphene into devices.…”