Spin Transport Properties of MnBi_(2)Te_(4)-Based Magnetic Tunnel Junctions

The van der Waals heterojunctions,stacking of different two-dimensional materials,have opened unprecedented opportunities to explore new physics and device concepts.Here,combining the density functional theory with non-equilibrium Green’s function technique,we systematically investigate the spin-polarized transport properties of van der Waals magnetic tunnel junctions(MTJs),Cu/MnBi_(2)Te_(4)/MnBi_(2)Te_(4)/Cu and Cu/MnBi_(2)Te_(4)/hBN/n·MnBi_(2)Te_(4)/Cu(n=1,2,3).It is found that the maximum tunnel magnetoresistance of Cu/MnBi_(2)Te_(4)/hBN/3·MnBi_(2)Te_(4)/Cu MTJs can reach 162.6%,exceeding the system with only a single layer MnBi_(2)Te_(4).More interestingly,our results indicate that Cu/MnBi_(2)Te_(4)/h-BN/n·MnBi_(2)Te_(4)/Cu(n=2,3)MTJs can realize the switching function,while Cu/MnBi_(2)Te_(4)/h-BN/3·MnBi_(2)Te_(4)/Cu MTJs exhibit the negative differential resistance.The Cu/MnBi_(2)Te_(4)/h-BN/3·MnBi_(2)Te_(4)/Cu in the parallel state shows a spin injection efficiency of more than 83.3%.Our theoretical findings of the transport properties will shed light on the possible experimental studies of MnBi_(2)Te_(4)-based van der Waals magnetic tunneling junctions.

Valley-polarized quantum anomalous Hall effect in van der Waals heterostructures based on monolayer jacutingaite family materials

We numerically study the general valley polarization and anomalous Hall effect in van der Waals(vdW)heterostructures based on monolayer jacutingaite family materials Pt2AX3(A=Hg,Cd,Zn;X=S,Se,Te).We perform a systematic study on the atomic,electronic,and topological properties of vdW heterostructures composed of monolayer Pt2AX3 and two-dimensional ferromagnetic insulators.We show that four kinds of vdW heterostructures exhibit valley-polarized quantum anomalous Hall phase,i.e.,Pt_(2)HgS_(3)/NiBr_(2),Pt_(2)HgSe_(3)/CoBr_(2),Pt_(2)HgSe_(3)/NiBr_(2),and Pt_(2)ZnS_(3)/CoBr_(2),with a maximum valley splitting of 134.2 meV in Pt_(2)HgSe_(3)/NiBr_(2) and sizable global band gap of 58.8 meV in Pt_(2)HgS_(3)/NiBr_(2).Our findings demonstrate an ideal platform to implement applications on topological valleytronics.

Enhanced robustness of zero-line modes in graphene via magnetic field

We systematically studied the influence of magnetic field on zero-line modes (ZLMs) in graphene and demonstrated the physical origin of their enhanced robustness by employing noneqnilibrium Green's functions and the Landauer Biittiker formula. We found that a perpendicular magnetic field can separate the wavefunctions of the counter-propagating kink states into opposite directions. Specifically, the separation vanishes at the charge neutrality point and increases as the Fermi level deviates from the charge neutrality point and can reach a magnitude comparable to the wavefunction spread at a moderate field strength. Such spatial separation of oppositely propagating ZLMs effectively suppresses backseattering and is more significant under zigzag boundary condition thail under armchair boundary condition. Moreover, the presence of magnetic field enlarges the bulk gap and suppresses the bound states, thereby further reducing the scattering. These mechanisms effectively increase the mean free paths of the ZLMs to approximately 1 |ini in the presence of a disorder.

Formation of topological domain walls and quantum transport properties of zero-line modes in commensurate bilayer graphene systems

We study theoretically the construction of topological conducting domain walls with a finite width between AB/BA stacking regions via finite element method in bilayer graphene systems with tunable commensurate twisting angles.We find that the smaller is the twisting angle,the more significant the lattice reconstruction would be,so that sharper domain boundaries declare their existence.We subsequently study the quantum transport properties of topological zero-line modes which can exist because of the said domain boundaries via Green’s function method and Landauer–Büttiker formalism,and find that in scattering regions with triintersectional conducting channels,topological zero-line modes both exhibit robust behavior exemplified as the saturated total transmission Gtot≈2e_(2)/h and obey a specific pseudospin-conserving current partition law among the branch transport channels.The former property is unaffected by Aharonov–Bohm effect due to a weak perpendicular magnetic field,but the latter is not.Results from our genuine bilayer hexagonal system suggest a twisting angle aroundθ≈0.1°for those properties to be expected,consistent with the existing experimental reports.

Equipartition of current in metallic armchair nanoribbon of graphene-based device

We numerically investigate the mesoscopic electronic transport properties of Bernal-stacked bilayer/trilayer graphene connected with four monolayer graphene terminals.In armchair-terminated metallic bilayer graphene,we show that the current from one incoming terminal can be equally partitioned into other three outgoing terminals near the charge-neutrality point,and the conductance periodically fluctuates,which is independent of the ribbon width but influenced by the interlayer hopping energy.This finding can be clearly understood by using the wave function matching method,in which a quantitative relationship between the periodicity,Fermi energy,and interlayer hopping energy can be reached.Interestingly,for the trilayer case,when the Fermi energy is located around the charge-neutrality point,the fractional quantized conductance 1/(4e 2h)can be achieved when system exceeds a critical length.

Quantum anomalous Hall effect and giant Rashba spin-orbit splitting in graphene system co-doped with boron and 5d transition-metal atoms

Quantum anomalous Hall effect （QAHE） is a fundamental quantum transport phenomenon in con- densed matter physics. Until now, the QAHE has only been experimentally realized for Cr/V-doped （Bi, Sb）2We3 but at an extremely low observational temperature, thereby limiting its potential appli- cation in dissipationless quantum electronics. By employing first-principles calculations, we study the electronic structures of graphene co-doped with 5d transition metal and boron atoms based on a com- pensated n-p co-doping scheme. Our findings are as follows： i） The electrostatic attraction between the n- and p-type dopants effectively enhances the adsorption of metal adatoms and suppresses their undesirable clustering, ii） Hf-B and Os-B co-doped graphene systems can establish long-range ferro- magnetic order and open larger nontrivial band gaps because of the stronger spin-orbit coupling with the non-vanishing Berry curvatures to host the high-temperature QAHE. iii） The calculated Rashba splitting energies in Re-B and Pt-B co-doped graphene systems can reach up to 158 and 85 meV, re- spectively, which are several orders of magnitude higher than the reported intrinsic spin-orbit coupling strength.