Miniband landscape of disordered dimer superlattices

Abstract

We investigate numerically the universal quantum fluctuations of the resistance and conductance in disordered dimer semiconductor superlattices. These systems exhibit sets of extended states (in spite of being disordered) due to the resonance induced by the dimer structure. We show that the transmission amplitude r (E) is a function of the energy of injected electrons and that its main characteristic is a "center" where r(E) ~ 1. This region of energy can be considered as consisting of weakly localized states proper of mesoscopic systems. On the other hand, the landscape of the allowed energies is a complex one, because close to the band edges, where r(E) « I, states are strongly localized. We attempt to understand these two regions by investigating the universal fluctuation properties of the resistance and conductance in both ofthem. We also hope that this study will contribute to the knowledge about universal fluctuations in mesoscopic systems.

Nature of the eigenstates in the miniband of random dimer-barrier superlattices

“…The different behaviour of the transition should be noticed: smooth for the lower energy and abrupt for the higher one. Qualitatively this finding is in agreement with the results obtained by Berman et al [28] where they consider the case of the RDQW. However as already noted before we should mention here that the RDB appears to be more relevant in suppressing localization than the RDQW, for the same concentration c = 0.4 the RDB reveals the existence of a plateau which spreads from E = 125 meV over a range of E = 54 meV, whereas in the case of RDQW the width of the plateau is about E = 2 meV [28].…”

“…1 reveals a remarkable feature: the curve of the conductance exhibits a high number of oscillations which are very close together in the regime of high conductance and low concentration and behaves rather smoothly in the band tails of the low conductance. Indeed in agreement with previous reports [28][29][30][31][32][33][34][35][36], in the absence of ensemble averages, the conductance presents several narrow peaks related to the number of the wells in the RDBSL displaying a transmittance close to l. It is apparent that even within the average procedure these peaks are reduced, they are robust enough to survive. This feature indicates the existence of different types of eigenstates: those having a high conductance close to the resonant energy and those with low conductance.…”

“…This is in the aim of finding experimentally measurable magnitudes and physically realizable situations, that confirm a clear validation of the theoretical model results, about the localization or delocalization electronic states in a quasi-1D system [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42].…”

“…Such results have been predicted by DominguezAdame, in the last decade, [28][29][30][31][32][33][34][35][36] introducing the correlated structural disorder by means of the so-called random dimer quantum wells superlattices (RDQWSL). In such a case, the resonant tunnelling [27] appears as the principal physical mechanism, breaking down the destructive interference introduced by disorder.…”

“…These fluctuations are known to be universal and inherent to any mesoscopic devices. Under the condition L < L φ quantum interference effects play a significant role, even in the presence of disorder [28]. The magnitude of the fluctuations discriminates the nature of the eigenstates.…”