Effect of Split Gate Size on the Electrostatic Potential and 0.7 Anomaly within Quantum Wires on a Modulation-DopedGaAs/AlGaAsHeterostructure

Abstract

We study 95 split gates of different size on a single chip using a multiplexing technique. Each split gate defines a one-dimensional channel on a modulation-doped GaAs/AlGaAs heterostructure, through which the conductance is quantized. The yield of devices showing good quantization decreases rapidly as the length of the split gates increases. However, for the subset of devices showing good quantization, there is no correlation between the electrostatic length of the one dimensional channel (estimated using a saddle point model), and the gate length. The variation in electrostatic length and the one-dimensional subband spacing for devices of the same gate length exceeds the variation in the average values between devices of different length. There is a clear correlation between the curvature of the potential barrier in the transport direction and the strength of the "0.7 anomaly": the conductance value of the 0.7 anomaly reduces as the barrier curvature becomes shallower. These results highlight the key role of the electrostatic environment in one-dimensional systems. Even in devices with clean conductance plateaus, random fluctuations in the background potential are crucial in determining the potential landscape in the active device area such that nominally identical gate structures have different characteristics.

Non-adiabatic single-electron pump in a dopant-free GaAs/AlGaAs 2DEG

“…Dopant-free field effect transistors have already been used to produce Hall bars, 39,44,46 quantum wires, [46][47][48][49][50] and quantum dots, [51][52][53][54][55][56] with demonstrated superior performance 39,44,46,49,50,53,54 in terms of low disorder, suppressed RTS noise, and cooldown-to-cooldown (even device-to-device) reproducibility relative to their modulation-doped counterparts. 39,44,46,50,57 In this Letter, we demonstrate non-adiabatic singleelectron pumps in dopant-free GaAs 2DEGs (see Fig. 1) with one-gate pumping, no visible random telegraph switching, operating in zero magnetic field at temperatures T > 1 K, and using a simple RF sine waveform up to 0.85 GHz.…”

Spin and valley degrees of freedom in a bilayer graphene quantum point contact: Zeeman splitting and interaction effects

“…In addition, this effect appears to be thermally activated and therefore not a ground-state property [74]. Moreover, experiments show that the confinement potential seems to play a crucial in the strength and the position of this conductance feature [82,83]. Recently, various explanations have been suggested to capture the physical origin of the 0.7 anomaly, such as dynamical spin polarization or spin gap models due to electron-electron interaction [58,74,75,90,93,94], Kondo effect [42-44, 89, 95-98], Wigner crystallization [99][100][101], or charge density waves [49] To our knowledge, no comprehensive study of the interaction-induced 0.7 anomaly in systems where both spin and valley degrees of freedom are degenerate has been reported so far.…”

“…As mentioned in the introduction, the 0.7 feature in the QPC conductance is seen as an additional kink below the lowest plateau sitting at around 0.7 × 2 e 2 h [41] for systems without additional degeneracies of the spectrum. It has been observed and extensively studied in quantum point contacts in GaAs/AlGaAs heterostructures for both electrons [41,43,47,55,57,[73][74][75][76][77][78][79][80][81][82][83], and holes [84][85][86][87][88][89][90]; signatures of the anomaly were also observed in Si/SiGe heterostructures [91].…”

Giant Magnetoresistance in a Chemical Vapor Deposition Graphene Constriction

“…A primary application of multiplexing is the statistical analysis of large data sets and identifying trends in data ensembles. 16 , 29 , 30 Statistical analysis identifies general behavior, allowing outliers to be selected and studied in detail. Our present work highlights the capability of our multiplexing system for an in depth study of the physics of such channels using numerous techniques including magnetic field, source–drain bias, and temperature from which one can obtain a detailed understanding of the fundamental phenomena.…”