Charge–pseudospin coupled diffusion in semi-Dirac graphene: pseudospin assisted valley transport

Abstract

Modifying the hexagonal lattices of graphene enables the repositioning and merging of the Dirac cones which proves to be a key element in the use of these materials for alternative electronic applications such as valleytronics. Here we study the nonequilibrium transport of carriers within a system containing two Dirac cones in both standard graphene and semi-Dirac graphene. In the latter, the lattice modifications cause the relativistic and parabolic dispersion bands to coexist, furnishing the Fermi surface with a rich pseudospin texture and a versatile Dirac cones separation. We construct a kinetic theory to investigate the carrier diffusion and uncover that the pseudospin index contributes to the particle current and, like the real spin, can induce a magnetoelectric effect, and argue that the pseudospin-charge coupling can be utilized to design a pseudospin filter. We explore the charge dynamics inside a quasi-one-dimensional conductor using the drift-diffusion model and detect the pseudospin accumulation at the sample boundaries. We find that, while, for graphene, the accumulation contributes to an extra voltage drop between the sample interfaces, the semi-Dirac system presents a similar accumulation that is strikingly equipped with valley polarization, signifying an essential tool for the control of valley manipulation and chirality transport using the pseudospin.

Kondo resonance effects in emergent flat band materials

“…The top panels of Figure 4 show the reversal of the charge pseudospin from +1.0 (at point K) to −1.0 (at point K') in the absence of carbon. Hence, introduction of carbon nanoline in the QD influences the pseudospin as well as the valley degrees of freedom for carrier transport [87]. The calculated electronic DOS (bottom panels) in the absence of carbon species shows a consistently wide bang gap-as expected.…”

The generation and detection of the spin-valley-polarization in semi-Dirac materials

“…By solving the BdG equation, we obtain the energy dispersions in the normal and the F region as ) , which are labeled as K and K¢ points. We notice that the valley in the merging-cone system is different from that in the pristine graphene [27,36]. There are four propagating modes near the Dirac points.…”

“…Such energy dispersion is a merging Dirac cones system, which can be produced experimentally in the honeycomb optical lattice [30,31], the TiO 2 /VO 2 heterostructures [32], and the phosphorus with situ deposition of K or Rb atoms [33]. Owing to its peculiar properties, the semi-Dirac materials with inverted gap have been investigated in valleytronics for potential applications [27,[34][35][36]. The transport of the electron from one valley can be inhibited when its pseudospin mismatches that of a gate-controlled scattering region, leading to a pseudospin-assisted valley-contrasting transport [27].…”

Quantum Shot Noise Signatures of Two-Dimensional Semi-Dirac System

“…SDMs has been realized in a large variety of systems, including (TiO 2 ) m /(VO 2 ) n nanostructure 18 , strained organic salt 19 , photonic crystals 20 , Bi 1-x Sb x 21 , striped boron sheet 22 , on surface states of topological insulators 23,24 , or in non-centrosymmetric systems 25 such phosphorus-based materials [26][27][28][29][30][31][32] , monolayer arsenene 33 , silicene oxide 34 , and polariton lattice 35 and also shown in α-dice lattice [36][37][38] with higher pseudospin. The electronic transport and shot noise of SDM have been studied extensively in previous works, which establish a Fano factor of F = 1 and F ≈ 0.179 at the band insulator phase with nonzero band gap and at the semimetallic gapless limit, respectively [38][39][40][41][42][43][44][45][46][47] . Nevertheless, 2D SDM can undergo complex topological phase transitions.…”

“…This parameter has been utilized for directional dependent transport 40,[52][53][54][55][56] and phase-dependent transport 36,44,57,58 . Owing to the presence of two inequivalent valleys in the band inversion phase (∆ < 0), band-inverted 2D SDMs have been widely studied for potential applications in valleytronics [44][45][46][47] .…”