10,596 research outputs found
Quasi-Ballistic Electron Transport in Random Superlattices
We theoretically study electron transport in disordered, quantum-well based,
semiconductor superlattices with structural short-range correlations. Our
system consists of equal width square barriers and quantum wells with two
different thicknesses. The two kinds of quantum wells are randomly distributed
along the growth direction. Structural correlations are introduced by adding
the constraint that one of the wells always appears in pairs. We show that such
correlated disordered superlattices exhibit a strong enhancement of their dc
conductance as compared to usual random ones, giving rise to quasi-ballistic
electron transport. Our predictions can be used to demonstrate experimentally
that structural correlations inhibit the localization effects of disorder. We
specifically describe the way superlattices should be built and experiments
should be carried out for that purpose.Comment: REVTeX 3.0, 7 pages, 4 figures on request from FD-A
([email protected]). Submitted to Physical Review B. Preprint
MA/UC3M/12/199
Absence of localization and large dc conductance in random superlattices with correlated disorder
We study how the influence of structural correlations in disordered systems
manifests itself in experimentally measurable magnitudes, focusing on dc
conductance of semiconductor superlattices with general potential profiles. We
show that the existence of bands of extended states in these structures gives
rise to very noticeable peaks in the finite temperature dc conductance as the
chemical potential is moved through the bands or as the temperature is
increased from zero. On the basis of these results we discuss how dc
conductance measurements can provide information on the location and width of
the bands of extended states. Our predictions can be used to demonstrate
experimentally that structural correlations inhibit the localization effects of
disorder.Comment: REVTeX 3.0, 14 pages, 11 figures available on request from ED
([email protected]). Submitted to Phys Rev B. MA/UC3M/06/9
Excitation decay in one-dimensional disordered systems with paired traps
Incoherent transport of excitations in one-dimensional disordered lattices
with pairs of traps placed at random is studied by numerically solving the
corresponding master equation. Results are compared to the case of lattices
with the same concentration of unpaired traps, and it is found that pairing of
traps causes a slowdown of the decay rate of both the mean square displacement
and the survival probability of excitations. We suggest that this result is due
to the presence of larger trap-free segments in the lattices with paired
disorder, which implies that pairing of traps causes less disruption on the
dynamics of excitations. In the conclusion we discuss the implications of our
work, placing it in a more general context.Comment: REVTeX 3.0, 10 pages, 7 figures available on request from FD-A
([email protected]), Universidad Carlos III preprint MA/UC3M/08/9
Dynamic transition in Landau-Zener-St\"uckelberg interferometry of dissipative systems: the case of the flux qubit
We study Landau-Zener-Stuckelberg (LZS) interferometry in multilevel systems
coupled to an Ohmic quantum bath. We consider the case of superconducting flux
qubits driven by a dc+ac magnetic fields, but our results can apply to other
similar systems. We find a dynamic transition manifested by a symmetry change
in the structure of the LZS interference pattern, plotted as a function of ac
amplitude and dc detuning. The dynamic transition is from a LZS pattern with
nearly symmetric multiphoton resonances to antisymmetric multiphoton resonances
at long times (above the relaxation time). We also show that the presence of a
resonant mode in the quantum bath can impede the dynamic transition when the
resonant frequency is of the order of the qubit gap. Our results are obtained
by a numerical calculation of the finite time and the asymptotic stationary
population of the qubit states, using the Floquet-Markov approach to solve a
realistic model of the flux qubit considering up to 10 energy levels.Comment: One new figure added. Final version to be published in PR
Incoherent Exciton Trapping in Self-Similar Aperiodic Lattices
Incoherent exciton dynamics in one-dimensional perfect lattices with traps at
sites arranged according to aperiodic deterministic sequences is studied. We
focus our attention on Thue-Morse and Fibonacci systems as canonical examples
of self-similar aperiodic systems. Excitons progressively extend over the
lattice on increasing time and, in this sense, they act as a probe of the
particular arrangements of traps in each system considered. The analysis of the
characteristic features of their time decay indicates that exciton dynamics in
self-similar aperiodic arrangements of traps is quite close to that observed in
periodic ones, but differs significatively from that corresponding to random
lattices. We also report on characteristic features of exciton motion
suggesting that Fibonacci and Thue-Morse orderings might be clearly observed by
appropriate experimental measurements. In the conclusions we comment on the
implications of our work on the way towards a unified theory of the orderings
of matter.Comment: REVTeX 3.0, 10 pages, 2 figures on request from FD-A
([email protected]). Submitted to Phys Rev B. MA/UC3M/11/9
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