Numerical simulation results are presented for a drift-diffusion rate equation model which describes electronic transport due to sequential tunneling between adjacent quantum wells in weakly coupled semiconductor supe...Numerical simulation results are presented for a drift-diffusion rate equation model which describes electronic transport due to sequential tunneling between adjacent quantum wells in weakly coupled semiconductor superlattices （SLs）. The electron dynamics is dependent on the external magnetic field perpendicular to the electron motion direction, and a detailed explanation is given. Using different parameters, the system shows different dynamic behaviors, and three distinct phenomena are observed and controlled by increasing magnetic field. （i） For a lower doping density, the system state transfers from stable state to oscillationary state. （ii） An opposite result is obtained to that in the case （i） for an intermediate value of the doping density, and the state changes from oscillationary to stationary. （iii） The state varies between oscillationary and stationary when doping density is large. Then, a detailed theoretical analysis is given to explain these surprise phenomena. The distribution of the electric-field domain along the SLs is plotted. We find the structure of the domain is almost uniform for a lower doping density, and no domain occurs in the SLs. By adding an external ac signal, complex nonlinear behaviors are observed from the Poincaré map and the corresponding phase diagrams when the driving frequency changes.展开更多
A theoretical model has been developed to study nonlinear behaviors in a GaAs/AlGaAs heterostructure. We show that the system can exhibit chaotic oscillations under transverse magnetic fields and an electric field.The...A theoretical model has been developed to study nonlinear behaviors in a GaAs/AlGaAs heterostructure. We show that the system can exhibit chaotic oscillations under transverse magnetic fields and an electric field.The time-delayed feedback method was applied to stabilize the unstable periodic orbits（UPOs） embedded in the chaotic attractor.A bifurcation specified by a successive decrease in the number of UPOs with delayed time and feedback strength was revealed,indicating the stabilization of UPOs under feedback control.Noticeably,the introduction of a feedback perturbation will sometimes induce chaotic states that do not exist in the unperturbed system.展开更多
The electronic and optical properties of graphene monoxide,a new type of semiconductor material,are theoretically studied by first-principles density functional theory.The calculated band structure shows that graphene...The electronic and optical properties of graphene monoxide,a new type of semiconductor material,are theoretically studied by first-principles density functional theory.The calculated band structure shows that graphene monoxide is a semiconductor with a direct band gap of 0.95 eV.The density of states of graphene monoxide and the partial density of states for C and O are given to understand the electronic structure.In addition,we calculate the optical properties of graphene monoxide,including the complex dielectric function,absorption coefficient, complex refractive index,loss-function,reflectivity and conductivity.These results provide a physical basis for potential application in optoelectronic devices.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11047108,11005003,U1204115,and 11005002)the Fund from the Science and Technology Department of Hennan Provice,China(Grant No.112300410183)the Science Foundation from the Education Department of Henan Province,China(Grant No.2011B140002)
文摘Numerical simulation results are presented for a drift-diffusion rate equation model which describes electronic transport due to sequential tunneling between adjacent quantum wells in weakly coupled semiconductor superlattices （SLs）. The electron dynamics is dependent on the external magnetic field perpendicular to the electron motion direction, and a detailed explanation is given. Using different parameters, the system shows different dynamic behaviors, and three distinct phenomena are observed and controlled by increasing magnetic field. （i） For a lower doping density, the system state transfers from stable state to oscillationary state. （ii） An opposite result is obtained to that in the case （i） for an intermediate value of the doping density, and the state changes from oscillationary to stationary. （iii） The state varies between oscillationary and stationary when doping density is large. Then, a detailed theoretical analysis is given to explain these surprise phenomena. The distribution of the electric-field domain along the SLs is plotted. We find the structure of the domain is almost uniform for a lower doping density, and no domain occurs in the SLs. By adding an external ac signal, complex nonlinear behaviors are observed from the Poincaré map and the corresponding phase diagrams when the driving frequency changes.
文摘A theoretical model has been developed to study nonlinear behaviors in a GaAs/AlGaAs heterostructure. We show that the system can exhibit chaotic oscillations under transverse magnetic fields and an electric field.The time-delayed feedback method was applied to stabilize the unstable periodic orbits（UPOs） embedded in the chaotic attractor.A bifurcation specified by a successive decrease in the number of UPOs with delayed time and feedback strength was revealed,indicating the stabilization of UPOs under feedback control.Noticeably,the introduction of a feedback perturbation will sometimes induce chaotic states that do not exist in the unperturbed system.
基金supported by the National Natural Science Foundation of China(Nos.11047108,11147197,11005003)the Research Project of Basic and Cutting-Edge Technology of Henan Province,China(No.112300410183)the Education Department of Henan Province, China(No.2011B140002)
文摘The electronic and optical properties of graphene monoxide,a new type of semiconductor material,are theoretically studied by first-principles density functional theory.The calculated band structure shows that graphene monoxide is a semiconductor with a direct band gap of 0.95 eV.The density of states of graphene monoxide and the partial density of states for C and O are given to understand the electronic structure.In addition,we calculate the optical properties of graphene monoxide,including the complex dielectric function,absorption coefficient, complex refractive index,loss-function,reflectivity and conductivity.These results provide a physical basis for potential application in optoelectronic devices.
