Condensed Matter

Spin-orbit coupling in two-dimensional systems is usually characterized by Rashba and Dresselhaus spin-orbit coupling (SOC) linear in the wave vector. However, there is a growing class of materials which instead support dominant SOC cubic in the wave vector (cSOC), while their superconducting properties remain unexplored. By focusing on Josephson junctions in Zeeman field with superconductors separated by a normal cSOC region, we reveal a strongly anharmonic current-phase relation and complex spin structure. An experimental cSOC tunability enables both tunable anomalous phase shift and supercurrent, which flows even at the zero-phase difference in the junction. A fingerprint of cSOC in Josephson junctions is the f-wave spin-triplet superconducting correlations, important for superconducting spintronics and supporting Majorana bound states.

Twisted bilayer graphene (TBG) aligned with hexagonal boron nitride (h-BN) substrate can exhibit an anomalous Hall effect at 3/4 filling due to the spontaneous valley polarization in valley resolved moiré bands with opposite Chern number [Science 367, 900 (2020), Science 365, 605 (2019)]. It was observed that a small DC current is able to switch the valley polarization and reverse the sign of the Hall conductance [Science 367, 900 (2020), Science 365, 605 (2019)]. Here, we discuss the mechanism of the current switching of valley polarization near the transition temperature, where bulk dissipative transport dominates. We show that for a sample with rotational symmetry breaking, a DC current may generate an electron density difference between the two valleys (valley density difference). The current induced valley density difference in turn induces a first order transition in the valley polarization. We emphasize that the inter-valley scattering plays a central role since it is the channel for exchanging electrons between the two valleys. We further estimate the valley density difference in the TBG/h-BN system with a microscopic model, and find a significant enhancement of the effect in the magic angle regime.

We investigate the joint effect of viscous and Ohmic dissipation on electric current flow through a slit in a barrier dividing a graphene sheet in two. In the case of the no-slip boundary condition, we find that the competition between the viscous and Ohmic types of the charge flow results in the evolution of the current density profile from a concave to convex shape. We provide a detailed analysis of the evolution and identify favorable conditions to observe it in experiment. In contrast, in the case of the no-stress boundary condition, there is no qualitative difference between the current profiles in the Ohmic and viscous limits. The dichotomy between the behavior corresponding to distinct boundary conditions could be tested experimentally.

In this study, we investigate the cyclotron resonance effect in the first-order AC current, magnetic ratchet effect, and second harmonic generation in phosphorene in the presence of a steady tilted magnetic field and under THz laser radiation. We establish that various cyclotron resonances exist in the deduced currents based on the angular frequency of the incoming light. These resonances are dependent on the ? c + value, a function of the carrier charge, the perpendicular magnetic field, and the effective masses along the armchair or zigzag edges. We discuss the direction and the magnitude of the deduced currents for various radiation polarizations. We compare the results with a zero perpendicular magnetic field. Cyclotron resonance for the first order AC current occurs at ?=± ? c + . The deduced current declines if the perpendicular magnetic field is zero. Meanwhile, for the ratchet current, cyclotron resonances occur at ?=± ? c + , ?=±2 ? c + , and radiation helicity affects the deduced current for circularly polarized light. Cyclotron resonance for the second harmonic generation current occurs at ?=± ? c + , ?=±2 ? c + and ?=± ? c + /2 and the current is stronger compared to the case with no perpendicular magnetic field. As the magnetic field rotates in the plane of anisotropic phosphorene, separate directions are predicted for the second harmonic generation--related current. It is noteworthy that the magnitude of the ratchet and second harmonic generation current are within the same range and comparable to the magnetic ratchet current in monolayer graphene, μA/cm .

Topological spin textures can be found in both two-dimensional and three-dimensional nanostructures, which are of great importance to advanced spintronic applications. Here we report the current-induced skyrmion tube dynamics in three-dimensional synthetic antiferromagnetic (SyAF) bilayer and multilayer nanostructures. It is found that the SyAF skyrmion tube made of thinner sublayer skyrmions is more stable during its motion, which ensures that a higher speed of the skyrmion tube can be reached effectively at larger driving current. In the SyAF multilayer with a given total thickness, the current-induced deformation of the SyAF skyrmion tube decreases with an increasing number of interfaces; namely, the rigidity of the SyAF skyrmion tube with a given thickness increases with the number of ferromagnetic (FM) layers. For the SyAF multilayer with an even number of FM layers, the skyrmion Hall effect can be eliminated when the thicknesses of all FM layers are identical. Larger damping parameter leads to smaller deformation and slower speed of the SyAF skyrmion tube. Larger fieldlike torque leads to larger deformation and a higher speed of the SyAF skyrmion tube. Our results are useful for understanding the dynamic behaviors of three-dimensional topological spin textures and may provide guidelines for building SyAF spintronic devices.

The interaction of DNA nucleobases with monolayer GaSe has been studied with in DFT framework using vdW functional. We found that nucleobases are physisorbed on the GaSe monolayer. The order of binding energy per atom is C > T > G > A. The room temperature recovery time estimated to be maximum of 113.88 micro sec. for T+GaSe indicting reusability of the GaSe based devices. The modulation in the electronic structures of GaSe has been clearly captured within the simulated STM measurements. We also demonstrate quantum capacitance as a key parameter for sensing applications. Furthermore, in optical properties, electron energy loss (EEL) spectra show red shift in photon energy on nucleobase adsorption in UV region. In nutshell, GaSe monolayer exhibit anisotropic optical response in UV-region which can be highly beneficial for developing polarized optical sensors. Our results demonstrate that GaSe monolayer can be utilized to fabricate reusable DNA sequencing devices for biotechnology and medical science.

A spatially oscillating pair potential ?(r)= ? 0 e 2iK?�r with momentum K> ? 0 /?�v drives a deconfinement transition of the Majorana bound states in the vortex cores of a Fu-Kane heterostructure (a 3D topological insulator with Fermi velocity v , on a superconducting substrate with gap ? 0 , in a perpendicular magnetic field). In the deconfined phase at zero chemical potential the Majorana fermions form a dispersionless Landau level, protected by chiral symmetry against broadening due to vortex scattering. The coherent superposition of electrons and holes in the Majorana Landau level is detectable as a local density of states oscillation with wave vector K 2 ?? ? 0 /?�v ) 2 ??????????????????????????. The striped pattern also provides a means to measure the chirality of the Majorana fermions.

The selective cooling of 75 As spins by optical pumping followed by adiabatic demagnetization in the rotating frame is realized in a nominally undoped GaAs/(Al,Ga)As quantum well. The rotation of 6 kG strong Overhauser field at the 75 As Larmor frequency of 5.5 MHz is evidenced by the dynamic Hanle effect. Despite the presence of the quadrupole induced nuclear spin splitting, it is shown that the rotating 75 As magnetization is uniquely determined by the spin temperature of coupled spin-spin and quadrupole reservoirs. The dependence of heat capacity of these reservoirs on the external magnetic field direction with respect to crystal and structure axes is investigated. The lowest nuclear spin temperature achieved is 0.54 μ K, which is the record low value for semiconductors and semiconductor nanostructures.

The dependences of the transport scattering time {\tau}t, quantum lifetime {\tau}q, and their ratio {\tau}t/{\tau}q on the density ne of the electron gas in modulation-doped single GaAs quantum wells with AlAs/GaAs short-period super-lattice barriers are investigated. The experimental dependences are explained in terms of electron scattering by remote ionized donors with an effective two-dimensional concentration n*R and background impurities with a three-dimensional concentration nB. An expression for n*R(ne) is obtained including the contribution of X-valley electrons localized in AlAs layers to the suppression of scattering by the random potential of remote donors. It is shown that the experimentally observed abrupt increase in {\tau}t and {\tau}q with an increase in ne above a certain critical value nec is related to a decrease in n*R. It is established that the drop in {\tau}t/{\tau}q observed for electron densities ne > nec occurs because scattering by the random potential of background impurities in this two-dimensional system with a decrease in n*R limits an increase in {\tau}t more considerably than an increase in {\tau}q.

Spin-orbit torque (SOT) magnetoresistance (MR) devices have attracted attention for use in next-generation MR devices. The SOT devices are known to exhibit different write properties based on the relative angle between the magnetization direction of the free layer and the write-current direction. However, few studies that compare the write properties of each type have been reported. In this study, we measured the external perpendicular-magnetic field dependence of the threshold write current density and the write current switching probability using two types of in-plane magnetization SOT-MR devices.