Spin-resolved edge states transport in a normal/ferromagnetic/normal topological insulator junction: The role of interface

The spin-resolved edge states transport in a normal/ferromagnetic/normal topological insulator (TI) junction is investigated numerically. It is shown that the transport properties of the hybrid junction strongly depend on the interface shape. For the junction with two sharp interfaces, a nonzero spin conductance can be generated besides the spin-split energy windows. Moreover, the axial symmetries of the in-plane spin conductance amplitude are broken. The underlying physics is attributed to the sharp-interface-induced quantum interference effect. However, for the hybrid junction with two smooth interfaces, a non-zero spin conductance can only be achieved in the spin-split energy windows. Further, the axial symmetries of the in-plane spin conductance amplitude recover. These findings may not only benefit to further apprehend the spin-dependent edge states transport in the hybrid TI junctions but also provide some theoretical bases to the application of the topological spintronics devices.     

Spin filter properties of armchair graphene nanoribbons with substitutional Fe atoms

ABSTRACT

The spin filter capability of a (0,8) armchair graphene nanoribbon with Fe atoms at substitutional sites is investigated by density functional theory in combination with the non-equilibrium Green's function technique. For specific arrangements, a high degree of spin polarisation is achieved. These include a single substitution at an edge position or double substitution in the central sector of the transmission element. The possibility of switching between majority and minority spin polarisation by changing the double substitution geometry is predicted. Including the bias dependence of the transmission function proves to be essential for correct representation of the spin-resolved current-voltage profiles.     

下地幔硅酸盐矿物的结构和电子相变对其高压下光学性质的影响

基于第一性原理平面波超软赝势法并结合局域密度近似,计算了(Mg_(0.875),Fe_(0.125))SiO_3钙钛矿和(Mg_(0.9),Fe_(0.1))SiO_3后钙钛矿晶体在高压下的光学性质.计算数据表明:(1)钙钛矿的结构相变将导致其吸收性增强,证实了基于实验数据的推断.(2)后钙钛矿二价铁吸收带的波数位置与实验观测结果相近.(3)在后钙钛矿相区,压力将导致吸收带的强度缓慢增加,但二价铁自旋态的转变对其吸收谱的影响却非常微弱.(4)钙钛矿的结构相变将导致其折射率升高;在后钙钛矿相区,压力及自旋态转变对折射率的影响不明显.(5)波数大约在12500 cm~(-1)以下,后钙钛矿折射率随波数的增加而降低,钙钛矿的折射率则变化不大;波数大约在12500 cm~(-1)以上,钙钛矿折射率随波数的增加而增大,后钙钛矿的折射率则显著上升.     

Observation of spin reorientation in layered manganites La1.2Sr1.8(Mn1−yRuy)2O7 (0.0⩽y⩽0.2) by Lorentz transmission electron microscopy

The effect of Ru substitution for Mn in bilayered oxides La_1.2Sr_1.8(Mn_1−yRu_y)₂O₇ (0?y?0.2$0?y?0.2$) was investigated by magnetization measurements and low-temperature Lorentz transmission electron microscopy. It was found that the magnetic anisotropy is controlled by the Ru content y and temperature T. The easy axis changes from 〈1 1 0〉 for the y=0$y=0$ crystal to the c  -axis for y=0.2$y=0.2$, and it rotates away from the c-  axis for the y=0.05$y=0.05$ and y=0.07$y=0.07$ crystals with decreasing temperature. Furthermore, maze-shaped magnetic domain structures were observed in the (0 0 1) thin crystals with 0.05?y?0.2$0.05?y?0.2$. Changes in domain size and structure indicate that the uniaxial magnetic anisotropy becomes stronger as Ru content y increases.     

On geometric SDPS-sets of elliptic dual polar spaces

Let n∈N?{0,1} and let K and K^′ be fields such that K^′ is a quadratic Galois extension of K. Let Q⁻(2n+1,K) be a nonsingular quadric of Witt index n in PG(2n+1,K) whose associated quadratic form defines a nonsingular quadric Q⁺(2n+1,K^′) of Witt index n+1 in PG(2n+1,K^′). For even n, we define a class of SDPS-sets of the dual polar space DQ⁻(2n+1,K) associated to Q⁻(2n+1,K), and call its members geometric SDPS-sets. We show that geometric SDPS-sets of DQ⁻(2n+1,K) are unique up to isomorphism and that they all arise from the spin embedding of DQ⁻(2n+1,K). We will use geometric SDPS-sets to describe the structure of the natural embedding of DQ⁻(2n+1,K) into one of the half-spin geometries for Q⁺(2n+1,K^′).     

Solutions of the spatially-dependent mass Dirac equation with the spin and pseudospin symmetry for the Coulomb-like potential

We study the effect of spatially-dependent mass function over the solution of the Dirac equation with the Coulomb potential in the (3+1)-dimensions for any arbitrary spin-orbit κ state. In the framework of the spin and pseudospin symmetry concept, the analytic bound state energy eigenvalues and the corresponding upper and lower two-component spinors of the two Dirac particles are obtained by means of the Nikiforov-Uvarov method, in closed form. This physical choice of the mass function leads to an exact analytical solution for the pseudospin part of the Dirac equation. The special cases , the constant mass and the non-relativistic limits are briefly investigated.     

Shubnikov-de Haas oscillations of massive Dirac fermions in a Dirac antiferromagnet SrMnSb2

We investigate the physical properties of massive Dirac fermions in SrMnSb₂ using transport, specific heat, electronic structure calculations, and Shubnikov-de Haas (SdH) oscillations. SrMnSb₂ is a candidate Dirac antiferromagnet, consisting of the MnSb layers and the distorted square net of Sb atoms with a zigzag chain structure. This structural distortion leads to gap opening at the band crossing point found in the square lattice of the sister compound SrMnBi₂ but leaves another Dirac band crossing near the Brillouin zone boundary. The small 2D Fermi surface with a light electron mass and a small Fermi energy is confirmed by the large resistivity anisotropy, the large Seebeck coefficient, and also the angle and temperature dependent SdH oscillations. The Berry phase obtained from the SdH oscillations is trivial, in contrast to the case of SrMnBi₂. The relatively large spin orbit coupling gap and the small Fermi energy in SrMnSb₂ is found to be essential to understand this contrasting behavior of the massive Dirac fermions as compared to SrMnBi₂. Our observations demonstrate that the Berry phase of the mobile electrons in SrMnSb₂ is sensitive to the Fermi level change and can be tuned by doping or deficiency.     

Quantum criticality of quantum speed limit for a two-qubit system in the spin chain with the Dzyaloshinsky–Moriya interaction

We study the quantum speed limit (QSL) time of a two-qubit system coupled to a spin–chain model with the Dzyaloshinsky–Moriya (DM) interaction. For the Bell state coupled to the Ising model or anisotropic XY model, we find that there is a prominent corresponding relationship between the QSL time and quantum phase transition in a spin–chain environment with larger scale, and the DM interaction can strongly enhance or suppress the response relation. Remarkably, when the surrounding environment is set to the XX model, the DM interaction makes it possible for us to witness the quantum phase transition by the local anomalous enhancement of the QSL time near the critical point. In addition, our analyses indicate that the entanglement can speed-up the system evolution in many-body environment.     

Spin-dependent transport properties of debrominated tetrabromopolyaromatic with Cu or Co doping embedded between zigzag graphene nanoribbon electrodes

Using density functional theory combined with non-equilibrium Green's function method, we investigate the spin-dependent transport properties of debrominated tetrabromopolyaromatic (D-TBPA) molecules embedded between zigzag graphene nanoribbon electrodes, and the effects of copper and cobalt side doping have also been considered. Our results show that the copper doping can insert new energy levels around the Fermi Level and keep spin degeneration of band structure, the cobalt doping can also induce spin splitting. The results on spin transport properties of D-TBPAs embedded into zigzag graphene nanoribbon electrodes show that these systems exist spin filtering and negative differential resistance behaviors. Corresponding physical mechanism on the spin-dependent transport property has been revealed according to the frontier molecular orbital characteristics.     

Spin and spin-valley Hall effects in a honeycomb lattice with antiferromagnetism and spin-orbit couplings

We study linear response to a longitudinal electric field on an antiferromagnetic honeycomb lattice with intrinsic and Rashba spin-orbit couplings (SOCs). It is found that the spin-valley Hall effect could emerge alone or coexist with the spin Hall effect. The spin and spin-valley Hall conductivities exhibit some peculiarities that depend on the distinct topological states of the graphene lattice. Furthermore, the spin and spin-valley Hall conductivities could be remarkably modulated by changing the Fermi level. Our findings suggest that the antiferromagnetic honeycomb lattice with SOCs is an excellent platform for potential applications of spintronics and valleytronics.