Can Yesilyurt

Efficient dual spin-valley filter in strained silicene

A two-barrier device is proposed in this work which can create valley-spin polarization and filtering function in strain engineered silicene. The device consists of two parts: 1) a region of uniaxial strain and exchange field arising from the adjacent top and bottom magnetic insulators, and 2) a region with magnetic field arising from two ferromagnetic stripes, and an electrochemical potential generated by top and bottom gates.

Perfect valley filter in strained graphene with single barrier region

We present a single barrier system to generate pure valley-polarized current in monolayer graphene. A uniaxial strain is applied within the barrier region, which is delineated by localized magnetic field created by ferromagnetic stripes at the region’s boundaries. We show that under the condition of matching magnetic field strength, strain potential, and Fermi energy, the transmitted current is composed of only one valley contribution. The desired valley current can transmit with zero reflection while the electrons from the other valley are totally reflected. Thus, the system generates pure valley-polarized current with maximum conductance. The chosen parameters of uniaxial strain and magnetic field are in the range of experimental feasibility, which suggests that the proposed scheme can be realized with current technology.

Klein tunneling in Weyl semimetals under the influence of magnetic field

Klein tunneling refers to the absence of normal backscattering of electrons even under the case of high potential barriers. At the barrier interface, the perfect matching of electron and hole wavefunctions enables a unit transmission probability for normally incident electrons. It is theoretically and experimentally well understood in two-dimensional relativistic materials such as graphene. Here we investigate the Klein tunneling effect in Weyl semimetals under the influence of magnetic field induced by ferromagnetic stripes placed at barrier boundaries. Our results show that the resonance of Fermi wave vector at specific barrier lengths gives rise to perfect transmission rings, i.e., three-dimensional analogue of the so-called magic transmission angles in two-dimensional Dirac semimetals. Besides, the transmission profile can be shifted by application of magnetic field in the central region, a property which may be utilized in electro-optic applications. When the applied potential is close to the Fermi level, a particular incident vector can be selected by tuning the magnetic field, thus enabling highly selective transmission of electrons in the bulk of Weyl semimetals. Our analytical and numerical calculations obtained by considering Dirac electrons in three regions and using experimentally feasible parameters can pave the way for relativistic tunneling applications in Weyl semimetals.

Influence of Fermi arc states and double Weyl node on tunneling in a Dirac semimetal

Most theoretical studies of tunneling in Dirac and the closely related Weyl semimetals have modeled these materials as single Weyl nodes described by the three-dimensional Dirac equation

Anomalous tunneling characteristic of Weyl semimetals with tilted energy dispersion

{boldsymbol{H}}{boldsymbol{=}}{{boldsymbol{v}}}_{{boldsymbol{f}}}overrightarrow{{boldsymbol{p}}}cdot overrightarrow{{boldsymbol{sigma }}}

The Hartman effect in Weyl semimetals

H=vfp→⋅σ→. The influence of scattering between the different valleys centered around different Weyl nodes, and the Fermi arc states which connect these nodes are hence not evident from these studies. In this work we study the tunneling in a thin film system of the Dirac semimetal Na3Bi consisting of a central segment with a gate potential, sandwiched between identical semi-infinite source and drain segments. The model Hamiltonian we use for Na3Bi gives, for each spin, two Weyl nodes separated in k-space symmetrically about kzu2009=u20090. The presence of a top and bottom surface in the thin film geometry results in the appearance of Fermi arc states and energy subbands. We show that (for each spin) the presence of two Weyl nodes and the Fermi arc states results in enhanced transmission oscillations, and finite transmission even when the energy falls within the bulk band gap in the central segment respectively. These features are not captured in single Weyl node models.

Electric field tunable Landau levels of Weyl semimetals in the absence of magnetic fields

We investigate the tunneling conductance of Weyl semimetal with tilted energy dispersion by considering electron transmission through a p-n-p junction with one-dimensional electric and magnetic barriers. In the presence of both electric and magnetic barriers, we found that a large conductance gap can be produced with the aid of tilted energy dispersion without a band gap. The origin of this effect is the shift of the electron wave-vector at barrier boundaries caused by (i) the pseudo-magnetic field induced by electrical potential, i.e., a newly discovered feature that is only possible in the materials possessing tilted energy dispersion, (ii) the real magnetic field induced by a ferromagnetic layer deposited on the top of the system. We use a realistic barrier structure applicable in current nanotechnology and analyze the temperature dependence of the tunneling conductance. The new approach presented here may resolve a major problem of possible transistor applications in topological semimetals, i.e., the ...

Strain-controlled valley and spin separation in silicene heterojunctions

Weyl semimetals are recently discovered states of quantum matter, which generally possess tilted energy dispersion. Here, we investigate the electron tunneling through a Weyl semimetal p-n-p junction. The angular dependence of electron tunneling exhibits an anomalous profile such that perfect transmission angles are shifted along the direction of the tilt. Coupling of the tilted dispersion and electrical potential within the barrier region gives rise to a transverse momentum shift, which is analogous to the transverse Lorentz displacement induced by magnetic barriers.