Polarization revival of a Bloch oscillating wave packet in conjunction with resonant Zener tunneling

We investigate the dynamics of a Bloch-oscillating wave packet in the presence of strong coupling to delocalized above barrier states (Zener tunneling), using time-resolved intraband polarization-sensitive measurements. At a threshold electric field, the resonance of localized and delocalized states causes a quantum beating which is observed as a revival in the intraband polarization. Our numerical simulation visualizes the spatial wave packet decomposition and reformation. The wave packet moves on a ps time scale over a distance of more than 100 nm and sequentially undergoes Bloch oscillations in the below- and above-barrier bands

Field-induced delocalization and Zener breakdown in semiconductor superlattices

We investigate the energy spectrum and the electron dynamics of a band in a semiconductor superlattice as a function of the electric field. Linear optical spectroscopy shows that, for high fields, the well-known localization of the Bloch states is followed by a field-induced delocalization, associated with Zener breakdown. Using time-resolved measurements, we observe Bloch oscillations in a regime where they are damped by Zener breakdown

Lifetime of Wannier-Stark states in semiconductor superlattices under strong Zener tunneling to above-barrier bands

For high electric fields, the lifetime of Wannier-Stark ladder states in a periodic potential is reduced by the fundamental process of Zener tunneling. We report on the analysis of the coherence lifetime of such states in semiconductor superlattices by interband spectroscopy. The reduction of lifetime by strong coupling between bands can only in the first approximation be described by the well-known Zener theory. A recently developed theoretical model is applied to calculate directly the tunneling probability of Wannier-Stark states as a function of the electric field. The theoretical results compare well with experiment, reproducing the complex interplay of both nonresonant and resonant Zener tunneling to higher bands. By comparing experiment and theory for a superlattice with a symmetric and one with a nonsymmetric potential, we can draw conclusions on a very general basis about the sensitive dependence of Zener tunneling on the specific dispersion relation of the carriers

Field-induced delocalization and Zener breakdown in semiconductor superlattices

We investigate the energy spectrum and the electron dynamics of a band in a semiconductor superlattice as a function of the electric field. Linear optical spectroscopy shows that, for high fields, the well-known localization of the Bloch states is followed by a field-induced delocalization, associated with Zener breakdown. Using time-resolved measurements, we observe Bloch oscillations in a regime where they are damped by Zener breakdown

Towards a Three-Dimensional Phase-Field Model of Dendritic Solidification with Physically Realistic Interface Width

We review the application of advanced numerical techniques such as adaptive mesh refinement, implicit time stepping, multigrid solvers and massively parallel implementations as a route to obtaining solutions to the three-dimensional phase-field problem with a domain size and interface resolution previously possible only in two dimensions. Using such techniques it is shown that such models are tractable even as the interface width approaches the solute capillary length

The Interplay of Intraband and Interband Polarization in the Ultrafast Response of Biased Semiconductor Superlattices

We present the results of a new excitonic formalism for the treatment of ultrafast dynamics in asymmetric semiconductor multiple quantum well structures. The method is infinite order in the optical field, with truncation of the infinite hierarchy of dynamical equations being accomplished via a factorization of six-particle correlation functions into a product of two- and four-particle ones. We use this formalism to calculate the THz emission and degenerate four-wave mixing signals from biased semiconductor superlattices under different excitation conditions. We present a number of density-dependent effects that demonstrate the central role that the intraband polarization plays in determining and modifying the nonlinear ultrafast response of the system

Wave function reconstruction in a graded well-width semiconductor superlattice

We experimentally reconstruct a Wannier-Stark wave function by spectrally resolving exciton wave packet interferences employing non-degenerate Four-Wave-Mixing spectroscopy. Excellent agreement with a numerical model is achieved