scholarly journals GRAPHENE IN THE QUANTUM HALL REGIME: EFFECTS OF VACANCIES, SUBLATTICE POLARIZATION AND DISORDER

2009 ◽  
Vol 23 (12n13) ◽  
pp. 2618-2627 ◽  
Author(s):  
ANA L. C. PEREIRA ◽  
PETER A. SCHULZ
Keyword(s):  
Quantum Hall ◽  
Tight Binding ◽  
Wave Functions ◽  
Hall Resistance ◽  
Monolayer Graphene ◽  
Binding Model ◽  
Quantum Hall Regime ◽  
Hall Regime ◽  
Valley Polarization ◽  
Disorder Effect

We investigate the effects of vacancies, disorder and sublattice polarization on the electronic properties of a monolayer graphene in the quantum Hall regime. Energy spectra as a function of magnetic field and the localization properties of the states within the graphene Landau levels (LLs) are calculated through a tight-binding model. We first discuss our results considering vacancies in the lattice, where we show that vacancies introduce extra levels (or well-defined bands) between consecutive LLs. An striking consequence here is that extra Hall resistance plateaus are expected to emerge when an organized vacancy superlattice is considered. Secondly, we discuss the anomalous localization properties we have found for the lowest LL, where an increasing disorder is shown to enhance the wave functions delocalization (instead of inducing localization). This unexpected effect is shown to be directly related to the way disorder increasingly destroys the sublattice (valley) polarization of the states in the lowest LL. The reason why this anomalous disorder effect occurs only for the zero-energy LL is that, in absence of disorder, only for this level all the states are sublattice polarized, i.e., their wave functions have amplitudes in only one of the sublattices.

INFLUENCE OF NEARBY QD LAYER ON 2DES IN QUANTUM HALL REGIME

2007 ◽  
Vol 21 (08n09) ◽  
pp. 1445-1449
Author(s):  
K. TAKEHANA ◽  
Y. IMANAKA ◽  
T. TAKAMASU ◽  
M. HENINI
Keyword(s):  
Magnetic Field ◽  
Transport Properties ◽  
Gate Voltage ◽  
Quantum Hall ◽  
Electron System ◽  
Hall Resistance ◽  
Field Range ◽  
Voltage Range ◽  
Quantum Hall Regime ◽  
Hall Regime

We have investigated transport properties in high magnetic field of a gated two-dimensional electron system (2DES) separated by a thin barrier from a layer of self-assembled InAs quantum dots (QDs) in the quantum Hall regime. The quality of 2DES was found to be high enough to observe both integer and fractional quantum Hall effect (QHE), despite the proximity of the QD layer to the 2DES. However, significant suppression of the magnetoresistance (ρ xx ) and Hall resistance (ρ xy ) were observed in higher magnetic field range of filling factor ν < 1 when a positive voltage was applied to the front gate. The gate voltage dependence of ρ xx and ρ xy shows a well-defined hysteresis loop at the narrow gate voltage range between -0.2 and +0.2 V at ν < 1, while no anomaly was observed at ν > 1. We deduce that charging and discharging of QDs occurs when the gate voltage is varied around Vg ~ 0 V, which indicates that the electron charge states of the QDs affect the transport properties of the nearby 2DES only at ν < 1. We infer that the spin-flip process induces a non-equilibrium state in the 2DEG, which causes the suppression of ρ xx and ρ xy .

scholarly journals Thermodynamics of free and bound magnons in graphene

2021 ◽  
Author(s):  
Andrew T. Pierce ◽  
Yonglong Xie ◽  
Seung Hwan Lee ◽  
Patrick R. Forrester ◽  
Di S. Wei ◽  
...  
Keyword(s):  
Thermodynamic Properties ◽  
Chemical Potential ◽  
Quantum Hall ◽  
Ferromagnetic Phase ◽  
Monolayer Graphene ◽  
Long Distance ◽  
Rotation Symmetry ◽  
Quantum Hall Regime ◽  
Hall Regime ◽  
Local Measurements

AbstractSymmetry-broken electronic phases support neutral collective excitations. For example, monolayer graphene in the quantum Hall regime hosts a nearly ideal ferromagnetic phase at specific filling factors that spontaneously breaks the spin-rotation symmetry1–3. This ferromagnet has been shown to support spin-wave excitations known as magnons that can be electrically generated and detected4,5. Although long-distance magnon propagation has been demonstrated via transport measurements, important thermodynamic properties of such magnon populations—including the magnon chemical potential and density—have not been measured. Here we present local measurements of electron compressibility under the influence of magnons, which reveal a reduction in the gap associated with the ν = 1 quantum Hall state by up to 20%. Combining these measurements with the estimates of temperature, our analysis reveals that the injected magnons bind to electrons and holes to form skyrmions, and it enables the extraction of free magnon density, magnon chemical potential and average skyrmion spin. Our methods provide a means of probing the thermodynamic properties of charge-neutral excitations that are applicable to other symmetry-broken electronic phases.

scholarly journals Hall resistance anomalies in the integer and fractional quantum Hall regime

2020 ◽  
Vol 102 (11) ◽  
Author(s):  
E. Peraticos ◽  
S. Kumar ◽  
M. Pepper ◽  
A. Siddiki ◽  
I. Farrer ◽  
...  
Keyword(s):  
Quantum Hall ◽  
Hall Resistance ◽  
Fractional Quantum ◽  
Fractional Quantum Hall ◽  
Quantum Hall Regime ◽  
Hall Regime

ANOMALOUS QUANTUM HALL RESISTANCE IN Al0.6Ga0.4As0.1Sb0.9/InAs QUANTUM WELL WITH TUNABLE CARRIER DENSITY

2007 ◽  
Vol 21 (08n09) ◽  
pp. 1419-1423
Author(s):  
K. OTO ◽  
S. TAMIYA ◽  
S. ISHIDA ◽  
A. OKAMOTO ◽  
I. SHIBASAKI
Keyword(s):  
Quantum Well ◽  
Carrier Transport ◽  
Chemical Potential ◽  
Lattice Mismatch ◽  
Quantum Hall ◽  
Hall Resistance ◽  
Persistent Photoconductivity ◽  
Quantum Hall Regime ◽  
Hall Regime ◽  
Magneto Resistance

We have investigated magneto-resistance in InAs/Al 0.6 Ga 0.4 As 0.1 Sb 0.9 quantum well (QW), where the lattice mismatch at the interface is less than 2 %. The carrier concentration can be tuned by using positive and negative persistent photoconductivity effect, selected by the wavelength (λ=1.6μ m or 0.95 μm) of illumination. The electrons and holes coexist in the QW structure, and the contribution of both carriers should be taken into account. The observed deviation of Hall plateaus from the quantized value can be understood by considering the carrier transport in both electron and hole edge channels, and the equilibrium of chemical potential at the all electrodes in the sample. The transport properties in quantum Hall regime measured in the samples with the QW thickness of 15, 50 and 150 nm are reported.

scholarly journals Magnetotransport of Monolayer Graphene with Inert Gas Adsorption in the Quantum Hall Regime

2018 ◽  
Vol 969 ◽  
pp. 012130 ◽  
Author(s):  
A Fukuda ◽  
D Terasawa ◽  
A Fujimoto ◽  
Y Kanai ◽  
K Matsumoto
Keyword(s):  
Gas Adsorption ◽  
Quantum Hall ◽  
Inert Gas ◽  
Monolayer Graphene ◽  
Quantum Hall Regime ◽  
Hall Regime

scholarly journals Nonlinear optics in the fractional quantum Hall regime

Nature ◽  
2019 ◽  
Vol 572 (7767) ◽  
pp. 91-94 ◽  
Author(s):  
Patrick Knüppel ◽  
Sylvain Ravets ◽  
Martin Kroner ◽  
Stefan Fält ◽  
Werner Wegscheider ◽  
...  
Keyword(s):  
Nonlinear Optics ◽  
Quantum Hall ◽  
Fractional Quantum ◽  
Fractional Quantum Hall ◽  
Quantum Hall Regime ◽  
Hall Regime
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