太赫兹场和倾斜磁场对超晶格电子动力学特性调控规律研究

Nonlinear electron transport in superlattice driven by a terahertz field and a tilted magnetic field

微带超晶格在磁场和太赫兹场调控下表现出丰富而复杂的动力学行为,研究微带电子在外场作用下的输运性质对于太赫兹器件设计与研制具有重要意义.本文采用准经典的运动方程描述了超晶格微带电子在沿超晶格生长方向(z方向)的THz场和相对于z轴倾斜的磁场共同作用下的非线性动力学特性.研究表明,在太赫兹场和倾斜磁场共同作用下,超晶格微带电子随时间的演化表现出周期和混沌等新奇的运动状态.采用庞加莱分支图详细研究了微带电子在磁场和太赫兹场调控下的运动规律,给出了电子运行于周期和混沌运动状态的参数区间.在电场和磁场作用下,微带电子将产生布洛赫振荡和回旋振荡,形成复杂的协同耦合振荡.太赫兹场与这些协同振荡模式之间的相互作用是导致电子表现出周期态、混沌态以及倍周期分叉等现象的主要原因.

Vertical electron transport in semiconductor superlattice has been the focus of science and technology during the past two decades due to the potential application of superlattice in terahertz devices. When driven by electromagnetic field, many novel phenomena have been found in superlattice. Here we study the chaotic electron transport in miniband superlattice driven by dcq-ac electric fields along the growth axis （z-axis） and a magnetic field tilted to z-axis using semiclassical equations of motion in the presence of dissipation. We calculate the electron momentum by changing the magnetic field or amplitude of the terahertz field. It is shown that the momentum p^（t） of miniband electron exhibits complicated oscillation modes while changing the control parameters. Poincar~ bifurcation diagram and power spectrum are adopted to analyze the nonlinear electron states. Poincare bifurcation diagram is obtained by plotting pyre = py （rnTac） （with m = 1, 2, 3, …. and Tac the period of ac terahertz field） as functions of ac amplitude E1 after the transients decay. The periodic and aperiodic regions can be distinguished from each other since there are a large number of points in the chaotic regions. When the magnetic field is increased from 1.5 to 2 T, the Poincare bifurcation diagram changes dramatically due to the strong effect of magnetic field on electron motion. The oscillating state of py （t） may be changed between periodic and chaotic syates. Power spectra of electron momentum pv for different values of El（= 2.06, 2.18, 2.388, and 2.72） are calculated for a deep insight into the nonlinear oscillating mode. It is found that the power spectra of n-periodic states show peaks at frequencies ifac/n （with i=1, 2, 3, … ）; the power spectra of chaotic states are very irregular with a large number of peaks. We demonstrate that the dissipation and resonance between Bloch oscillation frequency and cyclotron frequency play an important role in the electron transport process. We attribute the emerging of periodic and chaotic states in a superlattice to the interaction between terahertz radiation and internal cooperative oscillating mode related to Bloch oscillation and cyclotron oscillation. In the case of WB ≠ iwc, the time-dependent electron motion is chaotic in most regions of the parameter space. Results of the present paper are useful for designing terahertz devices based on the semiconductor superlattices.