Evidence of Inter-Landau-Level Tunneling in the Integral Quantum Hall Effect

Abstract

We have investigated conduction across electron density discontinuities induced by a front gate on GaAs/AUGai-jcAs single-interface heterostructures in the integral quantized Hall regime. When the gate is biased so that the Fermi level must cross between adjacent Landau levels at the gate edge, the boundary between higher-and lower-density regions behaves like a backward diode, suggesting the presence in these devices of inter-Landau-level tunneling.PACS numbers: 72.20. My, 73.40.Gk, 73.40.Kp, 85.30.Mn While electronic transport in the integral quantized Hall regime has by now been thoroughly studied, * most work has been confined to systems in which the carrier density is uniform. Nevertheless, density inhomogeneities in the two-dimensional electron gas (2DEG) can have important consequences. Recently, we have shown 2 that current can flow chiefly along the edges of 2DEG channels in the integral quantized Hall regime, probably because of the large density gradients occurring there. Woltjer et al. 3 have proposed an explanation for the integral quantized Hall effect in which electron density fluctuations, not localization, account for the presence of Hall plateaus. Syphers and Stiles 4 undertook an investigation of the potential distribution in contiguous regions of differing electron density, but failed to address the question of conduction across the density discontinuity.We have investigated the current-voltage (I-V) characteristics of abrupt density discontinuities in the integral quantized Hall regime. We have found that when the Fermi level (E?) must cross between adjacent Landau levels at the discontinuity, the I-V characteristic of the discontinuity is similar to that of a backward diode: When the device is forward biased (electrons flow from the high-density to the low-density region), conduction is small until a temperature-dependent threshold voltage is reached, when the current rapidly increases. When the device is reverse biased, the magnitude of / gradually increases with V, and is temperature independent. The similarity of our devices to backward diodes suggests that the conduction mechanisms are the same in both, implying the existence of inter-Landau-level tunnel currents across the discontinuity.Our experiments were performed on a GaAs/ Al x Gaix As single interface heterostructure with a 2DEG density of 5.

Landau level spin diode in a GaAs two dimensional hole system

“…The red trace in figure 1(c) is a typical IV trace measured in our device. We observe a strong nonlinear behaviour confirming that our device operates as a LL diode [12,14]. At low bias (− < < V 0.37 0.42 SD mV) only a very small current flows through the device (we call this the suppressed transport region).…”

“…This coupling is a major source of electron spin decoherence in GaAs spin qubits, because both Ga and As have nonzero nuclear spins. Several approaches have been developed to suppress this unwanted interaction [1,2], including NMR techniques such as spin-echo, dynamic nuclear polarization as well as the elimination of nuclear spins by using nuclear free materials such as 12 C or 28 Si. An alternative approach to minimising spin decoherence is to use hole spins since hyperfine coupling is much weaker than for electrons [3].…”

Dynamic nuclear polarization at the edge of a two-dimensional electron gas

“…Because of the different modes of transport for forward and negative bias, there should be an asymmetry in I. Previous experiments on transport between large compressible regions [17,19,20] and between spin-degenerate edge channels and large compressible regions [21] have shown this asymmetry.…”

Edge current switch of two-dimensional electron gas using carrier density control

“…Among the many efforts to manifest the edge channels in integral quantum Hall effect (IQHE), the inter-Landau-level tunneling in the IQHE [3] was proposed and the conduction across the electron density discontinuities induced by a gate put on the GaAs/ Al x Ga 12x As heterostructures was discussed. In that study, the gate was biased so that the Fermi level was crossed between the adjacent Landau levels at the gate edge, therefore the electron density discontinuities were induced.…”