GLOBAL ADIABATIC REGIME IN QUANTUM BALLISTIC TRANSPORT

We introduce the concepts of local and global adiabatic regimes in quantum ballistic transport and discuss the crossover between the two regimes. For a device consisting of microconstrictions and wider two-dimensional (2D) areas, local adiabaticity leads to the absence of mode mixing at the constrictions (L. I. Glazman, G. B. Lesovik, D. E. Khmelnitskii, and R. I. Shekhter, Pisma Zh. Eksp. Teor. Fiz. 48, 218 (1988) [JETP Lett. 48, 238 (1988)]). This condition ensures that the conductance of a constriction is quantized. Local adiabaticity is, however, not sufficient to ensure mode conservation during the propagation of an electron wave across the entire device. To reach such a global adiabatic regime a finite magnetic field has to be applied to the system. We have derived the necessary minimum strength of this field as a function of mode number and device geometry. A manifest signature of the global adiabatic regime is a single-period Aharonov-Bohm (AB) effect for a 2D cavity between two point contacts. We have derived the dependence of the AB period on magnetic field and mode number. Finally we also discuss the AB effect in an imperfect single-point-contact device with impurity-induced scattering. © 1990 The American Physical Society.