Orbit-Transfer Torque Driven Field-Free Switching of Perpendicular Magnetization

The reversal of perpendicular magnetization(PM)by electric control is crucial for high-density integration of low-power magnetic random-access memory.Although the spin-transfer torque and spin-orbit torque technologies have been used to switch the magnetization of a free layer with perpendicular magnetic anisotropy,the former has limited endurance because of the high current density directly through the junction,while the latter requires an external magnetic field or unconventional configuration to break the symmetry.Here we propose and realize the orbit-transfer torque(OTT),that is,exerting torque on the magnetization using the orbital magnetic moments,and thus demonstrate a new strategy for current-driven PM reversal without external magnetic field.The perpendicular polarization of orbital magnetic moments is generated by a direct current in a few-layer WTe_(2)due to the existence of nonzero Berry curvature dipole,and the polarization direction can be switched by changing the current polarity.Guided by this principle,we construct the WTe_(2)/Fe_(3)GeTe_(2)heterostructures to achieve the OTT driven field-free deterministic switching of PM.

Strain-dependent resistance and giant gauge factor in monolayer WSe_(2)

We report the strong dependence of resistance on uniaxial strain in monolayer WSe_(2)at various temperatures,where the gauge factor can reach as large as 2400.The observation of strain-dependent resistance and giant gauge factor is attributed to the emergence of nonzero Berry curvature dipole.Upon increasing strain,Berry curvature dipole can generate net orbital magnetization,which would introduce additional magnetic scattering,decreasing the mobility and thus conductivity.Our work demonstrates the strain engineering of Berry curvature and thus the transport properties,making monolayer WSe_(2)potential for application in the highly sensitive strain sensors and high-performance flexible electronics.

Strain Tunable Berry Curvature Dipole, Orbital Magnetization and Nonlinear Hall Effect in WSe_(2) Monolayer

The electronic topology is generally related to the Berry curvature,which can induce the anomalous Hall effect in time-reversal symmetry breaking systems.Intrinsic monolayer transition metal dichalcogenides possesses two nonequivalent K and K’ valleys,having Berry curvatures with opposite signs,and thus vanishing anomalous Hall effect in this system.Here we report the experimental realization of asymmetrical distribution of Berry curvature in a single valley in monolayer WSe_(2) via applying uniaxial strain to break C_(3v) symmetry.As a result,although the Berry curvature itself is still opposite in K and K’ valleys,the two valleys would contribute equally to nonzero Berry curvature dipole.Upon applying electric field E,the emergent Berry curvature dipole D would lead to an out-of-plane orbital magnetization M ∝ D·E,which further induces an anomalous Hall effect with a linear response to E^(2),known as nonlinear Hall effect.We show the strain modulated transport properties of nonlinear Hall effect in monolayer WSe_(2) with moderate hole-doping by gating.The second-harmonic Hall signals show quadratic dependence on electric field,and the corresponding orbital magnetization per current density M/J can reach as large as 60.In contrast to the conventional Rashba-Edelstein effect with in-plane spin polarization,such current-induced orbital magnetization is along the out-of-plane direction,thus promising for high-efficient electrical switching of perpendicular magnetization.

Magnetic field enhanced single particle tunneling in MoS2-superconductor vertical Josephson junction

As a prototypical transition-metal dichalcogenide semiconductor, MoS2 possesses strong spin–orbit coupling, which provides an ideal platform for the realization of interesting physical phenomena. Here, we report the magnetotransport properties in NbN–MoS2–NbN sandwich junctions at low temperatures. Above the critical temperature around ~11 K, the junction resistance shows weak temperature dependence, indicating a tunneling behavior. While below ~11 K, nearly zero junction resistance is observed, indicating the superconducting state in the MoS2 layer induced by the superconducting proximity effect. When a perpendicular magnetic field ~1 T is applied, such proximity effect is suppressed, accompanying with insulator-like temperature-dependence of the junction resistance. Intriguingly, when further increasing the magnetic field, the junction conductance is significantly enhanced, which is related to the enhanced single particle tunneling induced by the decrease of the superconducting energy gap with increasing magnetic fields. In addition, the possible Majorana zero mode on the surface of MoS2 can further lead to the enhancement of the junction conductance.

Possible collective band in neutron-rich^(119)Sn

Excited states of^(119)Sn have been studied using an in-beamγ-ray spectroscopic technique following the incomplete fusion of 7 Li on a^(116)Cd target at a beam energy of 42 MeV.A new bandlike structure is proposed to result from deformed two-particle-two-hole(2p-2h)proton excitations across the Z=50 closed shell based on the systematics of odd-A Sn isotopes and configuration-fixed constrained triaxial relativistic mean-field calculations.This observation extends the boundaries of the deformed 2p-2h collective band to A=119 in Sn isotopes.