Spin-polarized edge states of quantum Hall systems on silicon basis (original) (raw)
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Transport in quantum spin Hall edges in contact to a quantum dot
Physical Review B, 2016
We study the transport mechanisms taking place in a quantum spin Hall bar with an embedded quantum dot, where electrons localize and experience Coulomb interaction U as well as spin-flip processes λ. We solve the problem with non-equilibrium Green functions. We focus on the linear response regime and treat the many-body interactions with quantum Monte Carlo. The effects of U and λ are competitive and the induced transport takes place through different channels. The two mechanisms can be switched by changing the occupation of the dot with a gate voltage.
Fragility of Nonlocal Edge-Mode Transport in the Quantum Spin Hall State
Physical Review Applied, 2016
Non-local currents and voltages are better able at withstanding the deleterious effects of dephasing than local currents and voltages in nanoscale systems. This hypothesis is known to be true in quantum Hall setups. We test this hypothesis in a four terminal quantum spin Hall set up wherein we compare the local resistance measurement with the non-local one. In addition to inelastic scattering induced dephasing we also test resilience of the resistance measurements in the aforesaid setups to disorder and spin-flip scattering. We find the axiom that non-local resistance is less affected by the detrimental effects of disorder and dephasing to be in general untrue for quantum spin Hall case. This has important consequences since it has been widely communicated that non-local transport through edge channels in topological insulators will have potential applications in low power information processing.
Controlled Coupling of Spin-Resolved Quantum Hall Edge States
Physical Review Letters, 2011
We introduce and experimentally demonstrate a new method that allows us to controllably couple co-propagating spin-resolved edge states of a two dimensional electron gas (2DEG) in the integer quantum Hall regime. The scheme exploits a spatially-periodic in-plane magnetic field that is created by an array of Cobalt nano-magnets placed at the boundary of the 2DEG. A maximum charge/spin transfer of 28 ± 1% is achieved at 250 mK. 72.25.Dc, Topologically-protected edge states are dissipationless conducting surface states immune to impurity scattering and geometrical defects that occur in electronic systems characterized by a bulk insulating gap [1]. One example can be found in a clean two-dimensional electron gas (2DEG) under high magnetic field in the quantum Hall (QH) regime [2]. In the integer QH case, spinresolved edge states (SRESs) at filling fraction ν = 2 (number of filled energy levels in the bulk) are characterized by very large relaxation [3] and coherence [4] lengths. This system is a promising building block for the design of coherent electronics circuitry [4][5][6][7]. It represents also an ideal candidate for the implementation of dual-rail quantum-computation architectures [9] by encoding the qubit in the spin degree of freedom that labels two distinct co-propagating, energy-degenerate SRESs of the same Landau level (LL) at the same physical edge of the 2DEG [10]. A key element for the realization of such architecture [10-12] is a coherent beam splitter that makes it possible to prepare any superposition of the two logic states, thus realizing one-qubit gate transformations. This requires the ability to induce controlled charge transfer between the two co-propagating SRESs, a goal which up to date has not been yet achieved. Here we solve the problem by targeting a resonant condition, in analogy with the periodic poling technique adopted in optics .
Towards an Electronic Interferometer based on Spin-Resolved Quantum Hall Edge States
Journal of Physics: Conference Series, 2013
Spin resolved edge states are ideal candidates for the implementation of dual-rail quantum computation architectures by encoding the qubit in the spin degree of freedom of the co-propagating edge states. An important element for the realization of such architectures is a coherent beam splitter that controllably mixes the two co-propagating spin-resolved edge channels. Coupling of the spin resolved edge states is demonstrated recently by spin-flip scattering event that is induced by in-plane spatially-dependent periodic magnetic field of the nano-magnet array placed at the boundary of the mesa. In this paper we discuss the nanofabrication and our preliminary transport analysis of an electronic interferometer device made of two nano-magnetic arrays placed in close proximity. The impact of temperature in the coherent properties of the devices is addressed.
Proposal for a Datta-Das transistor in the quantum Hall regime
Physical Review B, 2012
We propose a mechanism to couple spin-resolved edge states in the integer quantum Hall effect by employing an array of voltage-controlled top gates. Strong enhancement of the coupling is achieved when the array periodicity matches the inverse of the wave-vector difference of the two states involved. Well known techniques of separately contacting the edge states make possible to selectively populate and read-out the edge states, allowing full spin read-out. Our device represents the quantum Hall version of the all-electrical Datta-Das spin-field effect transistor.
Cross-over between Magnetic and Electric Edges in Quantum Hall Systems
Physical Review B - Rapid Communiation, 2017
We report on the transition from magnetic edge to electric edge transport in a split magnetic gate device which applies a notch magnetic field to a two-dimensional electron gas. The gate bias allows tuning the overlap of magnetic and electric edge wavefunctions on the scale of the magnetic length. Conduction at magnetic edges-in the 2D-bulk-is found to compete with conduction at electric edges until magnetic edges become depleted. Current lines then move to the electrostatic edges as in the conventional quantum Hall picture. The conductivity was modelled using the quantum Boltzmann equation in the exact hybrid potential. The theory predicts the features of the bulk-edge cross-over in good agreement with experiment.
Mesoscopic Transport in Electrostatically Defined Spin-Full Channels in Quantum Hall Ferromagnets
Physical Review Letters, 2017
In this work we use electrostatic control of quantum Hall ferromagnetic transitions in CdMnTe quantum wells to study electron transport through individual domain walls (DWs) induced at a specific location. These DWs are formed due to hybridization of two counter-propagating edge states with opposite spin polarization. Conduction through DWs is found to be symmetric under magnetic field direction reversal, consistent with the helical nature of these DWs. We observe that long domain walls are in the insulating regime with localization length 4-6 µm. In shorter DWs the resistance saturates to a non-zero value at low temperatures. Mesoscopic resistance fluctuations in a magnetic field are investigated. The theoretical model of transport through impurity states within the gap induced by spin-orbit interactions agrees well with the experimental data. Helical DWs have required symmetry for the formation of synthetic p-wave superconductors. Achieved electrostatic control of a single helical domain wall is a milestone on the path to their reconfigurable network and ultimately to a demonstration of braiding of non-Abelian excitations.
Physica E: Low-dimensional Systems and Nanostructures, 2002
We report quantum magnetotransport experiments in novel 3 m-period V-grooved GaAs=AlGaAs heterojunctions. In such structures a periodic spatial variation of the normal component of magnetic ÿeld is realized. We observe anomalous features in both weak and strong magnetic ÿelds. The quantum Hall e ect step-like Hall resistance is replaced by an oscillatory variation when the current is applied parallel to the grooves. The longitudinal resistance peaks attain unusually high values h=e 2 when the current is applied perpendicular to the grooves. Most of the features can be explained by a model of serial and parallel connection of stripes with di erent ÿlling factors and di erent spin polarization at the adjacent stripes. ?