Resonance forerunners in superlattices

The existence of transient forerunners in multibarrier resonant structures is demonstrated. We use an analytic solution of the time-dependent Schrodinger equation for cutoff incident plane waves impinging on the potential, to explore the propagation phenomena of the transmitted quantum waves. For incidence energies below the first resonance, a series of propagating pulses (forerunners) are observed at the transmission side of the structure traveling faster than the main wavefront. In particular, it is shown that each forerunner propagates at the speed v(E-n)=[2mE(n)/(h) over bar (2)](1/2) associated to the nth resonance E-n, establishing a link between the sequence of forerunners and the resonance spectrum of the system.