We investigate the effect of Rashba spin-orbit coupling(RSOC)on photoconductivities of rectified currents in monolayer graphene with exchange field and sublattice potential.The system shows that the photoconductivitie...We investigate the effect of Rashba spin-orbit coupling(RSOC)on photoconductivities of rectified currents in monolayer graphene with exchange field and sublattice potential.The system shows that the photoconductivities of resonant shift and injection current contributions are nonzero,while the photoconductivities of non-resonant shift current contribution are zero.We find that the RSOC induces a warping term,which leads to the nonzero rectified currents.Moreover,the photoconductivities of resonant injection(shift)current contribution are(not)related to the relaxation rate.The similar behavior can be found in other Dirac materials,and our findings provide a way to tune the nonlinear transport properties of Dirac materials.展开更多
A novel theory of the commutating process of half/bridge thyristor are welding inverter is presented. According to the characteristic of its typical primary current pulse, a commutating process can be divided into th...A novel theory of the commutating process of half/bridge thyristor are welding inverter is presented. According to the characteristic of its typical primary current pulse, a commutating process can be divided into three stages. ie.. front-edge wave-head stage and back-edge stage.The equivalent circuits of each stage are presented respectively. For wave-head stage, the differential equation about the voltage across commutating capacitor has been set up with the initial condition of nonzero-current and nonzero-voltage. and its solutions are completely in accord with the practically measured waveforms. For front and back edge stages, the theory of current shifting on constant magnetic condition is introduced. The process, in which the inverse voltage across commutating capacitor is formed, and the rule, according to which the inverse voltage varies.are discussed. In addition. each. special operating state is studied carefully and a reasonable design state is determined. By T-type equivalent circuit in the design. state. the fundamental formulas for accurate engineering design are derived. Finally. two design cases are given.展开更多
Half-bridge circuit is taken as example, the physical essential of current pulse front edge and back edge in PWM of PFM converter is analyzed. The appearance of varying current-source or transfor- mation from voltage-...Half-bridge circuit is taken as example, the physical essential of current pulse front edge and back edge in PWM of PFM converter is analyzed. The appearance of varying current-source or transfor- mation from voltage-source into current-source in primary of converter is necessary condition for forming front and back edges. Through synchrenously varying of primary current and secondary current , and current shifting between two secondary windings in constant magnetic condition, transformation of basic Stages is realized.展开更多
It is well-known that exciton effects are determinant to understanding the optical absorption spectrum of low-dimensional materials.However,the role of excitons in nonlinear optical responses has been much less invest...It is well-known that exciton effects are determinant to understanding the optical absorption spectrum of low-dimensional materials.However,the role of excitons in nonlinear optical responses has been much less investigated at the experimental level.Additionally,computational methods to calculate nonlinear conductivities in real materials are still not widespread,particularly taking into account excitonic interactions.We present a methodology to calculate the excitonic second-order optical responses in 2D materials relying on:(i)ab initio tight-binding Hamiltonians obtained by Wannier interpolation and(ii)solving the Bethe-Salpeter equation with effective electron-hole interactions.Here,in particular,we explore the role of excitons in the shift current of monolayer materials.Focusing on MoS_(2)and GeS monolayer systems,our results show that 2p-like excitons,which are dark in the linear response regime,yield a contribution to the photocurrent comparable to that of 1s-like excitons.Under radiation with intensity~104W/cm2,the excitonic theory predicts in-gap photogalvanic currents of almost~10 nA in sufficiently clean samples,which is typically one order of magnitude higher than the value predicted by independent-particle theory near the band edge.展开更多
基金Project supported by the Shandong Province Natural Science Foundation(Grant No.ZR2021MF077)。
文摘We investigate the effect of Rashba spin-orbit coupling(RSOC)on photoconductivities of rectified currents in monolayer graphene with exchange field and sublattice potential.The system shows that the photoconductivities of resonant shift and injection current contributions are nonzero,while the photoconductivities of non-resonant shift current contribution are zero.We find that the RSOC induces a warping term,which leads to the nonzero rectified currents.Moreover,the photoconductivities of resonant injection(shift)current contribution are(not)related to the relaxation rate.The similar behavior can be found in other Dirac materials,and our findings provide a way to tune the nonlinear transport properties of Dirac materials.
文摘A novel theory of the commutating process of half/bridge thyristor are welding inverter is presented. According to the characteristic of its typical primary current pulse, a commutating process can be divided into three stages. ie.. front-edge wave-head stage and back-edge stage.The equivalent circuits of each stage are presented respectively. For wave-head stage, the differential equation about the voltage across commutating capacitor has been set up with the initial condition of nonzero-current and nonzero-voltage. and its solutions are completely in accord with the practically measured waveforms. For front and back edge stages, the theory of current shifting on constant magnetic condition is introduced. The process, in which the inverse voltage across commutating capacitor is formed, and the rule, according to which the inverse voltage varies.are discussed. In addition. each. special operating state is studied carefully and a reasonable design state is determined. By T-type equivalent circuit in the design. state. the fundamental formulas for accurate engineering design are derived. Finally. two design cases are given.
文摘Half-bridge circuit is taken as example, the physical essential of current pulse front edge and back edge in PWM of PFM converter is analyzed. The appearance of varying current-source or transfor- mation from voltage-source into current-source in primary of converter is necessary condition for forming front and back edges. Through synchrenously varying of primary current and secondary current , and current shifting between two secondary windings in constant magnetic condition, transformation of basic Stages is realized.
基金support from the Spanish MICINN(grants nos.PID2019-109539GB-C43,TED2021-131323B-I00,and PID2022-141712NB-C21)the María de Maeztu Program for Units of Excellence in R&D(grant no.CEX2018-000805-M)+2 种基金the Comunidad Autónoma de Madrid through the Recovery,Transformation and Resilience Plan from Spain,the NextGenerationEU plan from the European Union(MAD2D-CM-UAM7)the Generalitat Valenciana through Programa Prometeo(2021/017)The authors thankfully acknowledge RES resources provided by Universidad de Málaga in Picasso to FI-2024-2-0016.M.A.García-Blázquez acknowledges financial support from Universidad Autónoma de Madrid through an FPI-UAM grant.M.C.-G.is grateful to the Azrieli Foundation for the award of an Azrieli International Postdoctoral Fellowship.Additional computational resources were provided by the Weizmann Institute of Science at Chemfarm.M.C.-G.thanks Tonatiuh Rangel for providing the initial geometries of bulk and monolayer GeS.
文摘It is well-known that exciton effects are determinant to understanding the optical absorption spectrum of low-dimensional materials.However,the role of excitons in nonlinear optical responses has been much less investigated at the experimental level.Additionally,computational methods to calculate nonlinear conductivities in real materials are still not widespread,particularly taking into account excitonic interactions.We present a methodology to calculate the excitonic second-order optical responses in 2D materials relying on:(i)ab initio tight-binding Hamiltonians obtained by Wannier interpolation and(ii)solving the Bethe-Salpeter equation with effective electron-hole interactions.Here,in particular,we explore the role of excitons in the shift current of monolayer materials.Focusing on MoS_(2)and GeS monolayer systems,our results show that 2p-like excitons,which are dark in the linear response regime,yield a contribution to the photocurrent comparable to that of 1s-like excitons.Under radiation with intensity~104W/cm2,the excitonic theory predicts in-gap photogalvanic currents of almost~10 nA in sufficiently clean samples,which is typically one order of magnitude higher than the value predicted by independent-particle theory near the band edge.
