Bloch oscillations in a semiconductor superlattice shifting from capacitive to conductive responses with electric-field-induced interminiband mixing

We investigate the initial phase of Bloch oscillations in a GaAs-based superlattice designed for fine bias control of interminiband mixing. The type of oscillation current, determined from terahertz emission with the time origin (t=0), is found to shift gradually from damped cos ωBt to damped sin ωBt (ωB/2π: Bloch frequency) as the dc bias electric field is increased. This demonstrates a continuous transition between the capacitive and conductive responses, which have been previously reported in the two regimes where electron wavefunctions are Wannier–Stark localized within a nearly isolated miniband and delocalized by substantial interminiband mixing, respectively.