arXiv subjects

Mohsen Farokhnezhad

Publications and source records attributed to Mohsen Farokhnezhad.

5 recordsLinked to original sources

arXiv2024

Spin-orbit torques due to topological insulator surface states: an in-plane magnetization as a probe of extrinsic spin-orbit scattering

Topological insulator (TI) surface states exert strong spin-orbit torques. When the magnetization is in the plane its interaction with the TI conduction electrons is non-trivial, and is influenced by extrinsic spin-orbit scattering. This is expected to be strong in TIs but is difficult to calculate and to measure unambiguously. Here we show that extrinsic spin-orbit scattering sizably renormalizes the surface state spin-orbit torque resulting in a strong density dependence. The magnitude of the renormalization of the spin torque and the effect of spin-orbit scattering on the relative sizes of the in-plane and out-of-plane field-like torques have strong implications for experiment: We propose two separate experimental signatures for the measurement of its presence.

cond-mat.mes-hall↗

arXiv2022

Controllable giant magneto resistance and perfect spin filtering in $α^{\prime}$-borophene nanoribbons

By using non-equilibrium Green's function (NEGF) method and tight-binding (TB) approximation, we investigated a perfect control on spin transport in a zigzag $α^{\prime}$-boron nanoribbon ($α^{\prime}$-BNR) as the must semi-conducting structure of borophene. It has been found that when an $α^{\prime}$-BNR is exposed to an out-of-plane exchange magnetic field, spin splitting occurs for both spin-up and spin-down states in specific ranges of energy. Therefore, the spin polarization of current could be controlled by adjusting the energy of incoming electrons by means of an external back-gate voltage. We focus on the edge manipulation of $α^{\prime}$-BNR by ferro-magnetic (FM) or anti-ferromagnetic (AFM) exchange field which leads to the emergence of a giant magneto resistance and a perfect spin filtering. Local current provides the best picture of spin distribution of current in the nanoribbon. In order to observe the response of the system to the proximity effect of magnetic strips, we calculate the magnetic moment of each site. Then, we show that applying a transverse or perpendicular electric field in the presence of the exchange magnetic field gives another controlling tool on the spin polarization of current in a constant energy. Finally, by simultaneous effect of in-plane and out-of-plane exchange magnetic field on the edges of nanoribbon, we reach a control on spin rotation in the scattering region. Our investigation guarantees the $α^{\prime}$-BNR as a promising two dimensional (2D) structure for spintronic purposes.

cond-mat.mes-hall↗

arXiv2022

Spin-orbit torques from topological insulator surface states: Effect of extrinsic spin-orbit scattering on an out-of-plane magnetization

The origins of the spin-orbit torque (SOT) at ferromagnet/topological insulator (FM/TI) interfaces are incompletely understood. Theory has overwhelmingly focussed on the Edelstein effect due to the surface states in the presence of a scalar scattering potential. We investigate here the contribution to the SOT due to extrinsic spin-orbit scattering of the surface states, focusing on the case of an out-of-plane magnetization. We show that spin-orbit scattering brings about a sizable renormalization of the field-like SOT, which exceeds 20$\%$ at larger strengths of the extrinsic spin-orbit parameter. The resulting SOT exhibits a maximum as a function of the Fermi energy, magnetization, and extrinsic spin-orbit strength. The field-like SOT decreases with increasing disorder strength while the damping-like SOT is independent of the impurity density. With experimental observation in mind we also determine the role of extrinsic spin-orbit scattering on the anomalous Hall effect. Our results suggest extrinsic spin-orbit scattering is a significant contributor to the surface SOT stemming from the Edelstein effect when the magnetization is out of the plane.

cond-mat.mtrl-sci↗

arXiv2022

Quadrupolar photovoltaic effect in the terahertz range in a two-dimensional spin-3/2 hole system

We identify a strong photovoltaic response due to the non-linear optical transition between heavy and light hole sub-bands enabled by T_d-symmetry in a quantum well, which we term the quadrupolar photovoltaic effect (QPE). The photovoltaic current exhibits a strong resonance in the vicinity of the heavy hole-light hole splitting, with a magnitude governed by the momentum relaxation time, which can reach nanoseconds in GaAs holes. Since the heavy hole-light hole splitting can be tuned from a few meV to nearly 100 meV the QPE could serve as the basis for a terahertz photo-detector. We discuss strategies for experimental observation and device applications.

cond-mat.mes-hall↗

arXiv2021

Controllable spin filtering and half metallicity in $β_{12}$-borophene nanoribbons

The experimental observation of the Dirac fermion states in $β_{12}$-borophene sheets and the discovery of their novel topological properties properties have made them a promising candidate for spintronic applications. Here, by combining non-equilibrium Green's function (NEGF) and tight-binding (TB) approximation, we study the charge and spin transport properties through a $β_{12}$-borophene nanoribbon (BNR) with the different edge shapes. We show when a BNR exposed to a nonlocal exchange magnetic field, the spin filtering occurs for both spin-up and spin-down so that the spin direction of transmitted electrons could be controlled by adjusting the energy of incoming electrons with the help of an external backgate voltage. It is found that an armchair BNR (ABNR) in the simultaneous presence of a transverse electric field and a nonlocal exchange field indicates a half-metallic nature which is electrically controllable. Moreover, the influence of local exchange field fields is evaluated by exposing the edges of ABNR to ferromagnetic strips with parallel and antiparallel configurations. Our findings show that the edge manipulations in ABNRs lead to the emergence of a giant magnetoresistance and a perfect spin filter. Finally, we studied the effects of edge vacancies and Anderson disorder on the spin-dependent conductance of an ABNR and find that the perfect spin polarization is not destroyed in the presence of Anderson disorder and various single vacancies. Our results reveal the outstanding spin transport properties of ABNRs for future spintronic devices.

cond-mat.mes-hall↗