Evidence for a reentrant metal-insulator transition in quantum-dot arrays

Metal–insulator transition in quantum dot arrays

“…1 no obvious evidence for a dependence of the number of the metallic 'dips' on the component dot size, but instead suggest that this number is determined by the degree of disorder in the device. Indeed, studies of highly disordered arrays show no evidence for the metallic state whatsoever [2]. In order to more clearly demonstrate the observation of a metal-insulator transition, in Fig.…”

“…The motivation for these forms is discussed in detail in [2]. Basically, however, the exponential term is thought to represent the excitation of carriers across some characteristic energy gap (k B T 0 ).…”

“…Based on studies of the metal-insulator transition in two dimensions, we are able to propose a simple functional form that accounts reasonably well for the temperature-dependent variation of conductance observed in many cases. We also propose a basic mechanism for the implied metal-insulator transition, which appeals to the discrete form of the density of states in the mesoscopic arrays.Linear arrays consisting of three identical quantum dots connected in series were realized using the split gate technique [2]. Au-Ti gates were deposited on GaAs/AlGaAs heterojunction Hall bars, whose lowtemperature carrier density was 3.8×10 11 cm −2 and whose mobilities ranged from 2×10 5 to 10 6 cm 2 V −1 s −1 .…”

Current effects on high magnetic field resonances in a dot array

“…We study the temperature and current dependence of these peaks, and show that they are characterized by a relaxation time that is closer to the energy-relaxation time rather than the phase-coherence time, a result that seems at odds with their coherent nature. The basic device structure is the same as that discussed in [1][2][3][4], although this array has only three dots, which are formed by bias applied to standard 'split' gates on the surface of the material.In Fig. 1A, we plot the resistance as a function of temperature for this array.…”

“…Several resonances are observed on the side of the plateaus, which may be due either to charging of isolated islands or to transmission resonances in the quantum point contacts. Heating of the carriers causes these peaks to decrease with an energy relaxation time comparable to that of the dots themselves.c 2000 Academic Press Key words: quantum dots, magnetotransport, heterostructures.In recent months, studies of small arrays of open quantum dots have revealed new and interesting behavior, with onset of exponential localization at low temperatures, and a novel localization-delocalization transition at still lower temperatures [1,2]. It is found that carrier heating in these structures occurs with a characteristic energy-relaxation time [3] that is significantly different from the phase-breaking time [4].…”