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 g...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.展开更多
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 ...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.展开更多
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 technologie...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.展开更多
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 ...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.展开更多
Introducing ferromagnetism into non-magnetic systems without the participation of magnetic elements is promising for all-electric spintronic devices[1,2].Many approaches have been pursued,such as non-magnetic defects ...Introducing ferromagnetism into non-magnetic systems without the participation of magnetic elements is promising for all-electric spintronic devices[1,2].Many approaches have been pursued,such as non-magnetic defects induced magnetization in layered materials[3–5]or the inversion symmetry breaking induced magnetization in magic-angle bilayer graphene[6–8],etc.However,these approaches have to tackle with the localization effects or the inevitable precise control of twist angle,which hinders the future application into large-scale spintronic information devices.Theorists also predicted that the spontaneous ferromagnetism could emerge in the quasi-2D crystals[9]like GaSe,but no experimental results have been reported.Here,we report the spontaneous ferromagnetism induced by van Hove singularity[9–13]in non-magnetic groupⅣGe_(1–x)Sn_(x)alloys grown by the molecular beam epitaxy(MBE)technique.Our findings experimentally open up an opportunity to realize spintronics in groupⅣsemiconductors.展开更多
基金Project supported by the National Key Research and Development Program of China(Grant No.2018YFA0703703)the National Natural Science Foundation of China(Grant Nos.91964201,61825401,and 11774004).
文摘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.
基金Supported by the National Key Research and Development Program of China(Grant Nos.2018YFA0703703 and 2016YFA0300802)the National Natural Science Foundation of China(Grant Nos.91964201,61825401,and 11774004)。
文摘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.
基金supported by the National Natural Science Foundation of China(Grant Nos.91964201 and 61825401)。
文摘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.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2018YFA0703703 and 2016YFA0300802)the National Natural Science Foundation of China(Grant Nos.91964201,61825401,and 11774004).
文摘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.
基金supported by the National Natural Science Foundation of China (61825401 and 91964201)the Innovation Program for Quantum Science and Technology (2021ZD0302403)。
基金the Key-Area Research and Development Program of Guangdong Province(2020B0303060001,and 2018B030327001)the National Natural Science Foundation of China(61874109,61922077,12004158,and 12074162)+1 种基金the National Key Research and Development Program of China(2018YFB2200100,and 2020YFA0309300)Guangdong Provincial Key Laboratory(2019B121203002)。
文摘Introducing ferromagnetism into non-magnetic systems without the participation of magnetic elements is promising for all-electric spintronic devices[1,2].Many approaches have been pursued,such as non-magnetic defects induced magnetization in layered materials[3–5]or the inversion symmetry breaking induced magnetization in magic-angle bilayer graphene[6–8],etc.However,these approaches have to tackle with the localization effects or the inevitable precise control of twist angle,which hinders the future application into large-scale spintronic information devices.Theorists also predicted that the spontaneous ferromagnetism could emerge in the quasi-2D crystals[9]like GaSe,but no experimental results have been reported.Here,we report the spontaneous ferromagnetism induced by van Hove singularity[9–13]in non-magnetic groupⅣGe_(1–x)Sn_(x)alloys grown by the molecular beam epitaxy(MBE)technique.Our findings experimentally open up an opportunity to realize spintronics in groupⅣsemiconductors.
