Electric-field-driven insulating-to-conducting transition in a mesoscopic quantum dot lattice

Abstract

We investigate electron transport through a finite two dimensional mesoscopic periodic potential, consisting of an array of lateral quantum dots with electron density controlled by a global top gate. We observe a transition from an insulating state at low-bias voltages to a conducting state at high-bias voltages. The insulating state shows simply activated temperature dependence, with strongly gate voltage dependent activation energy. At low temperatures the transition between the insulating and conducting states becomes very abrupt and shows strong hysteresis. The high-bias behavior suggests underdamped transport through a periodic washboard potential resulting from collective motion. There has been great interest in understanding the motion of charge carriers in artificial periodic potentials with mesoscopic periods [1][2][3]. In particular, one might better understand transport in general by controlling the energy scales of importance: for quantum transport in such systems the important energies are the on-site excitation and Coulomb charging energies and the intersite tunneling matrix element. Control of these energies has been demonstrated in single lateral quantum dots connected by tunneling to leads, leading to insights into the Kondo effect [4], for example; similar insights into the Hubbard model might emerge from experiments on arrays of lateral quantum dots [5][6][7]. For classical transport modeled as charge diffusion through a tilted washboard potential, applicable to a wide variety of experimental systems [8][9][10], the energy scale is the height of the potential barrier between sites. In addition to the general question of whether quantum or classical transport dominates, artificial periodic potentials may provide insights into the extensive work on self-assembled arrays of semiconductor nanocrystals useful for optoelectronic devices [11,12].Many years ago, Duruöz et al. reported switching and hysteresis in an array of 200 × 200 lateral quantum dots in GaAs/AlGaAs heterostructures [13]. Subsequent experiments have been unable to reproduce these effects [14,15], raising the possibility that the observed hysteresis results from the leakeage current between the gate and dots observed by Duruöz et al. In this paper we report detailed measurements of the current through a 10 × 10 array of lateral quantum dots with a period of 340 nm. Like Duruöz et al., we find a hysteretic transition from a high resistance state at low bias to a low resistance state at high bias which is strongly tuned by magnetic field. Unlike previous measurements our devices have immeasurably small leakage between the gate and the dot array. We have studied the temperature, magnetic field, and gate-voltage (V g ) dependence of the transition in great detail. We find evidence that the important energy scale for transport within the high-resistance state is the barrier height between quantum dots. However, the low-resistance * nstaley@mit.edu state is quite unusual. While some of the features we observe are predicted by the simulati...

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