On the acoustoelectric current in a one-dimensional channel

Abstract

We report the first observation of the direct current induced by a surface acoustic wave through a quantum point contact defined in a GaAs-AlGaAs two-dimensional electron gas by means of a split gate. We have observed giant oscillations in the acoustoelectric current as a function of gate voltage, with minima corresponding to the plateaux in quantum point contact conductivity. A theoretical consideration is presented which explains the observed peaks in terms of the matching of sound velocity with electron velocity in the upper one-dimensional subband of the quantum point contact.The interaction of a surface acoustic wave (SAW) with a two-dimensional electron gas (2DEG) in a GaAs-Al x Ga 1−x As heterostructure has recently attracted much attention [1][2][3][4][5][6][7][8][9][10]. Usually, two kinds of effect are studied. The first kind is the attenuation and change in velocity of the sound wave due to interaction with electrons. For small amplitudes, these effects are linear in the acoustic wave amplitude. Analysis of these effects allows us, in principle, to study the linear response of carriers to alternating strain deformation and electric fields at the SAW frequency. An important consideration is that these measurements do not require any contacts to be made to the sample. Very interesting studies of these effects in quantum Hall systems were carried out, in particular, in [1,4].The second class of studies deal with the so-called acoustoelectric effects in 2DEGs. These are due to a drag of the 2D electrons by the SAW [5-10], and for small signals are quadratic in the SAW amplitude. As described, an acoustic wave, while travelling across the sample is attenuated due to interaction with the electrons, and transfers some of its momentum to them. As a result a d.c. current in a closed circuit appears (the acoustoelectric current). In an open circuit, a d.c. voltage is generated. Thus in principle these acoustoelectric effects can be used to study both the d.c. and a.c. response of the carriers.Drag of the electrons in a quantum point contact by non-equilibrium phonons has been considered in [11]. This paper discussed a current flowing through a channel due to a 'phonon wind' in the leads, and predicted its quantization, similar to the conductance quantization. We believe that such a mechanism is not important in our case, because of the strong screening of the interaction outside the QPC.In this letter we present the first experimental and theoretical study of the acoustoelectric current in a quasi-one-dimensional ballistic channel defined in a 2DEG by split-gate-induced depletion. We observed a very specific behaviour of the acoustoelectric current, qualitatively different from the behaviour of the conductance.

Giant acoustoelectric current in suspended quantum point contacts

“…We get both positive and negative oscillations prior to complete QPC pinch off. The positions of the oscillation peaks correspond to the one-dimensional plateaus seen at standard low-temperature transport measurements [9,13]. At the elevated temperatures of our experiment, the contributions of different subbands are not distinguishable anymore resulting in the washing out of the conductance steps.…”

“…These features support our conclusions of oscillations being consequences of the QPC subband structure. The wide broadening of the oscillations is due to the higher temperature at which our measurements were taken when compared to narrow oscillations of measurements at lower temperatures [12,13]. It should be emphasized that the spin splitting can be seen at quite low magnetic field (lower than that of Fig.…”

“…Similar results were obtained in Refs. [9,13,21,22] and several theoretical models were subsequently proposed [14,15].…”

Acoustoelectric effects in quantum constrictions

“…However, in many experiments using coherent SAWs [1] to induce the current, this is not the case. We should therefore investigate what happens with the acoustoelectric current at low frequencies, in particular, whenhω ≪ δE.…”

“…Namely, the variations in the sound velocity and attenuation are registered. The second group of experiments [1,2,7] is concentrated on the studies of the response of the electron gas to the acoustic waves. The quantities which are investigated in these experiments are the dc electric current induced by the waves (the so-called acoustoelectric current), or the dc voltage induced across the sample.…”