Coherent Excitonic Wavepackets in Two-Dimensional Square Dot Arrays Driven by an In-Plane Uniform Electric Field

We investigate the evolution behaviour of electron-hole pair wavepacket in optically excited square quantum-dot arrays driven by in-plane (x-y plane) uniform electric field E (viz, E = Exex Eyey, ex,ey are unit vectors along x and y directions respectively), in the time domain. It is found that if the ratio of the x-component electric field Ex to the y-component electric field Ey is a rational p/q (p and q being coprlme integer numbers), the wavepackets undergo a time-periodic breathing mode, with the period 2πp/ωBx, where ωBx=eExα/h, with a being the lattice constant of square dot arrays, h being Planck‘s constant, e being the electron charge. This finding provides a time-domain demonstration of the recent spectral result [Phys. Rev. Lett. 86 (2001) 3116].     

有局域场的三能级∧系统的瞬态解析结果

考虑Lorentz局域场效应的影响，我们在Liouville运动方程的基础上用微扰理论分析了一个三能级系统的非线性响应．在非线性光学响应中，两波矢分别为k1，k2的连续相干脉冲将会在新的方向产生新的光波．计算之后，我们给出四波混频信号关于Lorentz局域场因子l的表达式，发现负时间延迟时在2k2-k1方向仍有四波混频信号，四波混频信号的频率也有所改变．     

应力作用下石墨烯在磁场中的隧穿特性

研究了在垂直作用磁场驱动下的应变石墨烯单层的隧穿性质,通过转移矩阵给出了穿过一个磁势垒的透射率。研究发现在小角度散射中,与处于电势垒中的克莱因隧穿不同,磁场可以把电子束缚在一个应变的磁势垒中。只要入射能量不是很大,应变的存在可以显著增加定向透射率,这在技术应用中很重要,而大的入射能量能完全把应变的效应去除,使得应变的石墨烯和理想石墨烯几乎具有相同的隧穿性质。     

Tunneling current of the Coulomb-coupled quantum dots embedded in n-n junction

Taking account of the electron--electron (hole) and electron--hole interactions, the tunneling processes of the main quantum dot (QD) Coulomb-coupled with a second quantum dot embedded in n--n junction have been investigated. The eighteen resonance mechanisms involved in the tunneling processes of the system have been identified. It is found that the tunneling current depends sensitively on the electron occupation number in the second quantum dot. When the electron occupation number in the second dot is tiny, both the tunneling current peaks and the occupation number plateaus in the main QD are determined by the intra-resonance mechanism. The increase of the electron occupation number in the second dot makes the inter-resonance mechanism participate in the transport processes. The competition between the inter and intra resonance mechanisms persists until the electron occupation number in the second dot reaches around unity, leading to the consequence that the inter-resonance mechanisms completely dominate the tunneling processes.     

Coherent Dynamics of Direct-Current-Driven Quantum-Dot-Array with Two Time-Dependent Embedded Impurities

The coherent dynamics of dc-driven quantum-dot array with two embedded time-dependent impurities is investigated, the exact crossings and avoided crossings in the quasienergies are associated with the evolution dynamics of the electron by the introduction of the envelope lines of the site＇s maximum returning probability. Through a perturbative scheme, the time-dependent Hamiltonian is replaced by an equivalent static one, whose structure reveals the new quantum tunnelling mechanism in the time-periodic driving system and sheds light on the alternative interpretation of dynamic localization and delocalization.     

Local density of states of dc-biased superlattices with time-dependent imperfection

The single-particle Green's function for a dc-biased superlattices with single impurity potential varying harmonically with time has been obtained in the framework of U(t,t') method and Floquet--Green's function. The calculation of the local density of states shows that new states will emerge between the resonant Wannier--Stark states as a result of the intervention of time-dependent impurity potential, and the increase in electric field strength of impurity will result in the growing of the number of new states between the gaps of neighbouring Stark ladders.     

有局域场的三能级Λ系统的瞬态解析结果

考虑Lorentz局域场效应的影响,我们在Liouville运动方程的基础上用微扰理论分析了一个三能级系统的非线性响应.在非线性光学响应中,两波矢分别为k1,k2的连续相干脉冲将会在新的方向产生新的光波.计算之后,我们给出四波混频信号关于Lorentz局域场因子l的表达式,发现负时间延迟时在2k2-k1方向仍有四波混频信号,四波混频信号的频率也有所改变.     

交-直流势驱动下的应力石墨烯势垒中Dirac粒子的隧穿

研究了应力作用下单层石墨烯在含时电势垒中Dirac粒子的隧穿.通过改变势垒中交流势垒的强度、粒子的入射角、沿zigzag或armchair方向施加的应力等详细探讨了Dirac粒子经由中心带和边带的透射率.用数值计算证明了垂直入射时Klein遂穿是通过Dirac粒子经由各个边带的透射率的迭加而完全穿过受应力作用和交-直流势驱动下的势垒.一般情况下,增加交流势垒的强度会对透射产生抑制,但是,沿zigzag方向施加应力有利于Dirac粒子经由边带的透射而抑制经由中心带的透射.     

dc-ac驱动的半导体超晶格相干带内动力学非微扰方案

在非微扰方案下，通过对由静电场和含时电场驱动的光洙发半导体超晶格的带内相干动力学的数值研究，我们发现ＴＨｚ发射的模的时间积分信号可用来观察动力学局域化和光助传导。