INTRINSIC CHAOS IN A DC FIELD BIASED QUANTUM HETEROSTRUCTURE

A closed, quantum, double barrier, GaAs/AlGaAs heterostructure is made chaotic by adding a nonlinear potential term, alpha(Q(t)), to the tim e-dependent Schrodinger equation, and the dynamical behavior of an ele ctron cloud moving in the heterostructure biased by a de electric fiel d is examined numerically. Using phase-space diagrams, power spectrums , and Lyapunov exponents, both qualitative and quantitative measures o f the chaos in the system were taken. In general, for all values of al pha, the nonlinearity parameter, the Lyapunov exponent, lambda, increa ses as the applied de field, beta, increases. However, for values of a lpha less than or equal to 1.376, we notice a sharp drop in lambda for the value of beta =-9.2x10(7) V/m corresponding to an average de volt age of -.085 eV in the central well. This first order type transition to high values of lambda for alpha>1.376 corresponds to a similar incr ease in the mean charge trapped in the heterostructure and in the aver age nonlinear potential in the central well for that dc field. This be havior is attributed to the fact that for alpha less than or equal to 1.376 and beta=-9.2x10(7) V/m, the field effects dominate, but for alp ha>1.376, the nonlinearity term dominates. (C) 1997 American Institute of Physics.