Showing papers on "Magnetocapacitance published in 1998"

Self-consistent analysis of a quantum capacitor

Abstract: We analyze the behavior of the magnetocapacitance for a three-probe capacitor. The self-consistent evaluation of the internal potential is found to play a large role in determining quantitative values of the capacitance. For capacitor plates of mesoscopic size, this potential reduces the charge accumulation by more than an order of magnitude compared to that obtained with noninteracting models. However, the qualitative behavior of the magnetocapacitance is not substantially altered by the self-consistency. A simple but physically motivated model gives an analytical formula which compares well with the numerical data.

Magnetic-field-induced hybridization of electron subbands in a coupled double quantum well

Abstract: We employ a magnetocapacitance technique to study the spectrum of the soft two-subband (or double-layer) electron system in a parabolic quantum well with a narrow tunnel barrier at the center. In this system, when unbalanced by gate depletion, two sets of quantum oscillations are observed at temperatures T≳30 mK: one originates from the upper electron subband in the closer-to-the-gate part of the well, and the other indicates the existence of common gaps in the spectrum at integer fillings. For the lowest filling factors υ=1 and υ=2, both the presence of a common gap down to the point of the one-to two-subband transition and their nontrivial magnetic field dependences point to magnetic-field-induced hybridization of electron subbands.

Magnetocapacitance in quantum Hall regime with external dc current

Abstract: We have investigated the magnetocapacitance between gates and two dimensional electron system in a GaAs/AlGaAs heterostructure with an external dc current at quantum Hall (QH) plateau regime. With increasing dc current, the minimum values of capacitance at QH plateaux increase and the range of magnetic fields showing the capacitance minima decreases. The electrons excited by the external dc current enhance the σ XX which causes the breakdown of the QH effect. In a certain magnetic field and current direction, the capacitance dip at QH plateau splits into two valleys with dc current. These results are considered to be due to the change of effective gate voltage caused by the current. The breakdown current of the QH effect evaluated by the resistance measurement is several times larger than that obtained by the dc current dependence of the magnetocapacitance, since the capacitance is very sensitive to the residual σ XX . The vanishing of the capacitance minima may be the precursor of QH breakdown.

Edge channels in integer and fractional quantum-Hall regime investigated by magnetocapacitance

Abstract: We have evaluated the width of edge channels in the fractional and integer quantum-Hall (QH) regime by the magnetocapacitance measurement between a gate and two-dimensional electron system in GaAs/AlGaAs heterostructures. The frequency dependence of the magnetocapacitance between 100 Hz and 1 MHz has been measured at temperatures between 35 mK and 0.4 K. At the fractional QH regime, the total width of the edge channels is found to be 2.5 and 9 μm at 35 mK at the QH plateaux of filling factor ν= 1 3 and 2 3 , respectively. In the integer QH regime, the temperature dependence of the edge channel width is almost flat in the range of 35 mK–0.4 K. At the QH plateau of ν=1 due to spin-splitting Landau level, the width of total edge channel is almost the same value with that at ν=2. The width at ν=3 is also comparable to that at ν=4, although the residual bulk conductivity of ν=3 is an order of magnitude larger than that of ν=4.

Magnetocapacitance and Edge States

Abstract: The spatial distribution of edge states at quantum Hall (QH) plateaus has been studied both experimentally and theoretically. In the classical simple picture, the width of the edge states is expected to be of the order of the cyclotron radius, since the electrons move along the sample edge by a skipping motion as shown in Fig. 3.3.1. In the one-electron quantum mechanical picture, the width of the edge states is also of the order of the magnetic length \( l = \sqrt {\hbar /e{\rm B}} \).