Hysteresis in the Quantum Hall Regimes in Electron Double-Quantum-Well Structures

Abstract

We present in this paper experimental results on the transport hysteresis in electron double quantum well structures. Exploring the measurement technique of fixing the magnetic field and sweeping a front gate voltage (Vg), we are able to study the hysteresis by varying the top layer Landau level fillings while maintaining a relatively constant filling factor in the bottom layer, allowing us to tackle the question of the sign of Rxx(up)-Rxx(down), where Rxx(up) is the magnetoresistance when Vg is swept up and Rxx(down) when Vg swept down. Furthermore, we observe that hysteresis is generally stronger in the even integer quantum Hall effect (IQHE) regime than in the odd-IQHE regime. This, we argue, is due to a larger energy gap for an even-IQHE state, determined by the Landau level separation, than that for an odd-IQHE state, determined by the Zeeman splitting.There is a great deal of current interest in the study of the double quantum well (DQW) structures 1 . Compared to a single layer of the two-dimensional electron or hole system (2DES or 2DHS), the existence of another layer introduces significant interaction effects between two quantum wells. Over the years, many novel physical phenomena have been observed 2,3,4,5,6,7,8,9,10 . In addition, since the distance (or the coupling) between the two quantum wells can be controllably tuned from a few tenths of nanometer to several microns, DQW structures have shown promise as possible future electronic devices for next generation information processing 11 . Recently, a new phenomenon has been discovered in the DQW structures: electronic transport hysteresis 12,13 . It was observed that, when the densities of two wells are different and tunneling is negligible, the magnetotransport coefficients show hysteretic behavior when the magnetic (B) field is swept up and down. This hysteretic behavior occurs when only one QW is in the integer quantum Hall effect (IQHE) regime, and is believed to be due to a spontaneous charge transfer between the two layers 12 . Specifically, when one layer enters into an IQHE state, its Fermi level jumps from one Landau level to another. Consequently, the chemical potential between the two QW's becomes unbalanced. In reaching an equilibrium state, a spontaneous charge transfer from one QW to the other will occur, via the ohmic contacts. Since one QW is in the IQHE regime where the bulk is insulating, redistribution of the transferred charges takes a finite time to reach completion. This finite time constant, combined with the finite sweeping rate of the B field, gives rise to a hysteresis in electronic transport.This hysteretic electronic transport was first observed in a single, high electron mobility quantum well with a low mobility parallel conducting channel 12 , and later in hole DQW structures 13 . So far, no studies have been conducted in the most common DQW structures, the electron DQW's. Thus, questions remain whether the hysteresis is universal and occurs in electron DQW's.In this paper, we present experimental results of the transpo...