Keywords: 
• 太赫兹 /
• 超晶格 /
• 混沌 /
• 分支图

Abstract: 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 dc+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 py (t) of miniband electron exhibits complicated oscillation modes while changing the control parameters. Poincaré bifurcation diagram and power spectrum are adopted to analyze the nonlinear electron states. Poincaré bifurcation diagram is obtained by plotting pym =py (mTac) (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 Poincaré 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 py for different values of E1(= 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 ofωB?=iωc, 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.