Showing papers on "Spin-½ published in 2022"

Spin logic operations based on magnetization switching by asymmetric spin current

Abstract: Spintronic devices based on spin orbit torques (SOT) exhibit advantages in low power consumption, high speed, reconfigurability, and high endurance, which offers the prospect of in-memory computing based on spin logic devices. By designing a local spin current gradient, the magnetization can be switched deterministically by asymmetric spin currents without external magnetic field using micromagnetic simulations, where an additional out of plane effective field can be generated by the spin gradient. Through capping half of the Pt/Co/Pt SOT devices with Pt strip, we demonstrate the field-free deterministic current-induced magnetization switching experimentally. Finally, we design AND, NAND, OR, and NOR Boolean logic gates based on these devices, which could be used as building blocks for programmable and stateful logic operations.

Tunable electronic structure and Rashba spin splitting of WSe2/WS2 van der Waals heterostructure via strain and electric-field

Abstract: Suitable band structure, effective carrier separation and spin-charge locking are critical for further development and application of nanoscale spintronic devices. In this work, the effects of in-plane biaxial strain and electric field on the electronic structures and Rashba spin splitting of WSe 2/WS2 van der Waals heterostructure are investigated by the first principles calculations. The results show that considering the SOC effect, an observable Dresselhaus spin splitting of 424.5 meV and Rashba spin splitting can be observed at the K and Γ point in the valence band, respectively. At the same time, unexpected circle-type Berry curvature occurs due to a broken mirror structure for the WSe 2/WS2 heterostructure . A largest Rashba parameter α R with 0.503 eV A can be achieved at the strain of −4% and the positive electronic field tend to weaken the strength of Rashba spin splitting. The linear Rashba spin splitting strength of WSe2/WS2 heterostructure is tried to clarify, and coexistence of valley-contrasting property and Rashba effect enables spintronics and valleytronics application can be achieved. These results provide a way to engineer the electronic structure and Rashba spin splitting of WSe2/WS2 heterostructure and open up the possibilities for exploring spin logic electronic devices as well as valleytronic devices.

Semiclassical anisotropic transport theory in two dimensional pseudo-spin one system

Abstract: In this paper we calculate the Drude–Boltzmann conductivity for two dimensional pseudo-spin one systems, in the presence of isotropic and anisotropic scattering mechanisms. To this end, we employ the Boltzmann equation in the relaxation time approximation and solve it analytically while taking into account an explicit angular dependence in the transport time. For pseudo-spin independent disorder the conductivity is isotropic. For pseudo-spin dependent scattering, the conductivity can be isotropic or anisotropic, depending on the matrix structure of the potential scattering. We outline possible implications of anisotropic scattering in the theory of quantum transport .

Non-equilibrium spin polarization in magnetic two-dimensional electron gas with k-linear and k-cubed Dresselhaus spin–orbit interaction

Abstract: The current-induced spin polarization (CISP) of charge carriers is one of the main mechanisms of spin-to-charge interconversion effects that can be used in new spintronics devices. Here, CISP is studied theoretically in symmetric quantum wells growing in [001] crystallographic direction, where both k -linear and k -cubed Dresselhaus spin–orbit interactions are present. The exchange interaction responsible for perpendicular to plane net magnetization is also taken into account. The main focus is on the influence of cubic Dresselhaus term on CISP and the interplay between spin–orbit interaction (SOI) and the exchange field. The analytical and numerical results are derived within the linear response theory and Matsubara Green’s function formalism. Apart from detailed numerical results, we also provide some analytical expressions that may be useful for interpretation of experimental results and for characterization of quantum wells with Dresselhaus SOI. Analytical expressions for the relevant Berry curvature are also derived, and it is shown that the Berry curvature in magnetic 2DEG with cubic Dresselhaus interaction oscillates in the k -space, while its averaged value is reduced. We also analyze the temperature behavior of CISP and calculate the low-temperature spin polarizability due to heat current.

Dynamical properties of the Haldane chain with bond disorder

Abstract: By using Lanczos exact diagonalization and quantum Monte Carlo combined with stochastic analytic continuation, we study the dynamical properties of the $S=1$ antiferromagnetic Heisenberg chain with different strengths of bond disorder. In the weak disorder region, we find weakly coupled bonds which can induce additional low-energy excitation below the one-magnon mode. As the disorder increases, the average Haldane gap closes at $\delta_{\Delta}\sim 0.5$ with more and more low-energy excitations coming out. After the critical disorder strength $\delta_c\sim 1$, the system reaches a random-singlet phase with prominent sharp peak at $\omega=0$ and broad continuum at $\omega>0$ of the dynamic spin structure factor. In addition, we analyze the distribution of random spin domains and numerically find three kinds of domains hosting effective spin-1/2 quanta or spin-1 sites in between. These "spins" can form the weakly coupled long-range singlets due to quantum fluctuation which contribute to the sharp peak at $\omega=0$.

Spatiotemporal characteristics of spin transport in compensated metals with electron-hole exchange interaction.

Abstract: We develop a theory describing spatiotemporal behavior of spin transport in two-band metals by postulating a spin-exchange interaction between electrons and holes. Starting with the semiclassical Boltzmann equation, we derive a system of coupled diffusion equations and solve them analytically under steady-state conditions. The solutions reveal two types of electron-hole coupled-spin transport modes: a dissipative mode and a nondissipative mode with an infinite spin diffusion length. The two modes are the manifestations of two types of spin coupling channels. Besides the exchange interaction, we incorporate into our derivation the relaxation caused by the spin-orbit interaction to show how it affects the spin transport characteristics of the two modes.

Optimal dense coding and quantum phase transition in Ising-XXZ diamond chain

Abstract: We theoretically propose a dense coding scheme based on an infinite spin- 1 / 2 Ising-XXZ diamond chain, where the Heisenberg spins dimer can be considered as a quantum channel. Using the transfer-matrix approach, we can obtain the analytical expression of the optimal dense coding capacity χ . The effects of anisotropy, external magnetic field, and temperature on χ in the diamond-like chain are discussed, respectively. It is found that χ is decayed with increasing the temperature, while the valid dense coding ( χ > 1 ) can be carried out by tuning the anisotropy parameter. Additionally, a certain external magnetic field can stimulate the enhancement of dense coding capacity. In an infinite spin- 1 / 2 Ising-XXZ diamond chain, it has been shown that there exist two kinds of quantum phase transitions (QPTs) in zero-temperature phase diagram, i.e., one is that the ground state of system changes from the unentangled ferrimagnetic state to the entangled frustrated state and the other is from the entangled frustrated state to the unentangled ferromagnetic state. Here, we propose that optimal dense coding capacity χ can be regarded as a new detector of QPTs in this diamond-like chain, and the relationship between χ and QPTs is well established.

Bias pulse-controlled thermal spin injector based a single-molecule magnet tunneling junction

Abstract: An electric pulse-controlled thermal spin injector is theoretically proposed, which consists of a junction with a single-molecule magnet sandwiched between the ferromagnetic and nonmagnetic leads. By applying a temperature gradient and a time-varying bias pulses across the junction, the spin direction of the single-molecule magnet can be controlled to be antiparallel or parallel to the magnetization of the ferromagnetic lead by a spin-transfer torque effect, and the spin polarization of thermoelectric current tunneling through this junction can be switched from + 100 % to − 100 % corresponding to a molecule’s spin orientation, respectively. Our numerical results show that the spin polarization of the thermoelectric current will not be easily affected by the magnetization of electrodes, which can be fully and precisely tuned in electric manner. This device scheme can be compatible with current technologies and has potential applications in future spin caloritronics devices.

Coexisting unconventional Rashba- and Zeeman-type spin splitting in Pb-adsorbed monolayer WSe2.

Abstract: Based on first-principles calculations, the unconventional Rashba- and Zeeman-type spin splitting can simultaneously coexist in the Pb-adsorbed monolayer WSe2system. The first two adsorption configurationst1andt2show remarkable features under the spin-orbit coupling, in which two split energy branches show same spin states at the left or right side of Γ, and the spin polarization is reversed for both Rashba band branches. For the second adsorption configuration, an energy gap was observed near the unconventional spin polarization caused by the repelled Rashba bands for avoid crossing, and this gap can produce non-dissipative spin current by applying the voltage. The results fort2configuration with spin reversal show that the repel band gap and Rashba parameter can be effectively regulated within the biaxial strain range of -8% to 6%. By changing the adsorption distancedbetween Pb and the neighboring Se atom layer, the reduceddcaused the transfer from Rashba-type to Zeeman-type spin splitting. This predicted adsorption system would be promising for spintronic applications.

Quantum Monte Carlo study of topological phases on a spin analogue of Benalcazar-Bernevig-Hughes model.

Abstract: We study the higher-order topological spin phases based on a spin analogue of Benalcazar-Bernevig-Hughes model in two dimensions using large-scale quantum Monte Carlo simulations. A continuous Neel-valence bond solid quantum phase transition is revealed by tuning the ratio between dimerized spin couplings, namely, the weak and strong exchange couplings. Through the finite-size scaling analysis, we identify the phase critical points, and consequently, map out the full phase diagrams in related parameter spaces. Particularly, we find that the valence bond solid phase can be a higher-order topological spin phase, which has a gap for spin excitations in the bulk while demonstrates characteristic gapless spin modes at corners of open lattices. We further discuss the connection between the higher-order topological spin phases and the electronic correlated higher-order phases, and find both of them possess gapless spin corner modes that are protected by higher-order topology. Our result exemplifies higher-order physics in the correlated spin systems and will contribute to further understandings of the many-body higher-order topological phenomena.