Correlated bilayer electron states

Shayegan, M.; Manoharan, Hari C.; Suen, Y. W.; Lay, T. S.; Santos, M. B.

doi:10.1088/0268-1242/11/11s/015

Cited by 25 publications

(74 citation statements)

References 21 publications

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“…Moreover, for a given well width, the 1/2 and 1/4 FQHSs weaken and eventually disappear when the density is reduced and ∆ SAS is sufficiently increased. These observations were taken as evidence that these FQHSs are 2C [9,15,16,17,18].Here we report the observation of ν = 1/2 and 1/4 FQHSs in WQWs with very significant charge distribution asymmetry and large subband separation. Ironically, when the charge distribution is made symmetric and the subband splitting is lowered, the states disappear.…”

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confidence: 58%

“…When electrons at very low n are confined to a modulation-doped WQW, they occupy the lowest electric subband and have a single-layer-like (but rather thick in the growth direction) charge distribution. As more electrons are added to the well, their electrostatic repulsion forces them to pile up near the well's walls and the charge distribution appears increasingly bilayer-like [15,16,17,18]. At such n the electrons typically occupy the lowest two, symmetric and antisymmetric, electric subbands which are separated in energy by ∆ SAS .…”

Section: Pacs Numbersmentioning

confidence: 99%

“…However, there has been no experimental evidence up to now that such a state exists. FQHSs at ν = 1/2 have been seen in bilayer ESs in either double [13] or wide [14,15,16,17] quantum well (DQW or WQW) systems; a FQHS at ν = 1/4 was also observed recently in WQWs [18,19]. In both DQW and WQW systems, when the interlayer tunneling is small, the 1/2 state is well described by the 2C Ψ 331 wavefunction; in this case the "components" are the layer indices or, alternatively, the two (symmetric and antisymmetric) electric subbands.…”

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confidence: 99%

“…According to theory a MRP FQHS, obeying non-Abelian statistics, can exist at ν = 1/2 [7,9,10,11,12]. Experiments, however, have shown that the ν = 1/2 (and 1/4) FQHSs observed in WQWs are stable only when the overall charge distribution in the well is nearly symmetric ("balanced") and that the states disappear when the distribution is made asymmetric ("imbalanced") [15,16,17,18]. Moreover, for a given well width, the 1/2 and 1/4 FQHSs weaken and eventually disappear when the density is reduced and ∆ SAS is sufficiently increased.…”

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confidence: 99%

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confidence: 99%

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Evidence for Developing Fractional Quantum Hall States at Even Denominator1/2and1/4Fillings in Asymmetric Wide Quantum Wells

et al. 2009

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We report the observation of developing fractional quantum Hall states at Landau level filling factors ν = 1/2 and 1/4 in electron systems confined to wide GaAs quantum wells with significantly asymmetric charge distributions. The very large electric subband separation and the highly asymmetric charge distribution at which we observe these quantum Hall states, together with the fact that they disappear when the charge distribution is made symmetric, suggest that these are one-component states, possibly described by the Moore-Read Pfaffian wavefunction. PACS numbers:Even-denominator fractional quantum Hall states (FQHSs), observed in very high quality two-dimensional (2D) electron systems (ESs) have been enigmatic. In standard, single-layer 2D ESs confined to GaAs/AlGaAs heterojunctions or to narrow GaAs quantum wells, evendenominator FQHSs are observed only in the excited Landau levels, primarily at filling factor ν = 5/2 [1, 2, 3].It is yet not known whether the spin degree of freedom is necessary to stabilize this state [3]. If yes, then the 5/2 state could be described by a two-component (2C) Laughlin-Halperin (Ψ 331 ) wavefunction [4]. But if it is stable in a fully spin-polarized 2D ES, then it is likely to be the one-component (1C) Moore-Read Pfaffian (MRP) state [5]. The latter is of particular interest as it is expected to obey non-Abelian statistics and have potential use in topological quantum computing [6].The possibility of a 1C FQHS at even-denominator ν in the lowest Landau level, e.g. at ν = 1/2, has been theoretically discussed in numerous publications [5,7,8,9,10,11,12]. However, there has been no experimental evidence up to now that such a state exists. FQHSs at ν = 1/2 have been seen in bilayer ESs in either double [13] or wide [14,15,16,17] quantum well (DQW or WQW) systems; a FQHS at ν = 1/4 was also observed recently in WQWs [18,19]. In both DQW and WQW systems, when the interlayer tunneling is small, the 1/2 state is well described by the 2C Ψ 331 wavefunction; in this case the "components" are the layer indices or, alternatively, the two (symmetric and antisymmetric) electric subbands. In bilayer systems with strong tunneling (large symmetric-to-antisymmetric subband splitting, ∆ SAS ), on the other hand, the situation is unclear. According to theory a MRP FQHS, obeying non-Abelian statistics, can exist at ν = 1/2 [7,9,10,11,12]. Experiments, however, have shown that the ν = 1/2 (and 1/4) FQHSs observed in WQWs are stable only when the overall charge distribution in the well is nearly symmetric ("balanced") and that the states disappear when the distribution is made asymmetric ("imbalanced") [15,16,17,18]. Moreover, for a given well width, the 1/2 and 1/4 FQHSs weaken and eventually disappear when the density is reduced and ∆ SAS is sufficiently increased. These observations were taken as evidence that these FQHSs are 2C [9,15,16,17,18].Here we report the observation of ν = 1/2 and 1/4 FQHSs in WQWs with very significant charge distribution asymmetry and large subband separation. Ironical...

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confidence: 58%

Section: Pacs Numbersmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Evidence for Developing Fractional Quantum Hall States at Even Denominator1/2and1/4Fillings in Asymmetric Wide Quantum Wells

et al. 2009

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Temperature dependent symmetry to asymmetry transition in wide quantum wells

Oylumluoglu

Mirioglu

Aksu

et al. 2015

Physica E: Low-dimensional Systems and Nanostructures

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Quasi-two dimensional electron systems exhibit peculiar transport effects depending on their density profiles and temperature. A usual two dimensional electron system is assumed to have a δ like density distribution along the crystal growth direction. However, once the confining quantum well is sufficiently large, this situation is changed and the density can no longer be assumed as a δ function. In addition, it is known that the density profile is not a single peaked function, instead can present more than one maxima, depending on the well width. In this work, the electron density distributions in the growth direction considering a variety of wide quantum wells are investigated as function of temperature. We show that, the double peak in the density profile varies from symmetric (similar peak height) to asymmetric while changing the temperature for particular growth parameters. The alternation from symmetric to asymmetric density profiles is known to exhibit intriguing phase transitions and is decisive in defining the properties of the ground state wavefunction in the presence of an external magnetic field, i.e from insulating phases to even denominator fractional quantum Hall states. Here, by solving the temperature and material dependent Schrödinger and Poisson equations self-consistently, we found that such a phase transition may elaborated by taking into account direct Coulomb interactions together with temperature.

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Composite fermions in a wide quantum well in the vicinity of the filling factor 1/2

Drichko

Smirnov

Suslov

et al. 2019

Solid State Communications

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Using acoustic method we study dependences of transverse AC conductance, σ(ω), on magnetic field, temperature and the amplitude of AC electric field in a wide (75 nm) quantum well (QW) structure focusing on the vicinity of the filling factor ν = 1/2. Measurements are performed in the frequency domain 30-307 MHz and in the temperature domain 20-500 mK. Usually, in wide QW structures closely to ν = 1/2 the fractional quantum Hall effect (FQHE) regime is realized at some parameters of the sample. However, in our structure, at ν = 1/2 it is a compressible state corresponding to gas of composite fermions which is observed. This is confirmed by apparent frequency independence and weakly decreasing temperature dependence of Re σ(ω). Comparing the dependences of this quantity on temperature and power of the acoustic wave we conclude that the observed nonlinear behavior of the conductance is compatible with heating of the composite fermions by the acoustic wave. For comparison, we also study the vicinity of ν = 3/2 where the FQHE regime is clearly observed.

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Correlated bilayer electron states

Cited by 25 publications

References 21 publications

Evidence for Developing Fractional Quantum Hall States at Even Denominator1/2and1/4Fillings in Asymmetric Wide Quantum Wells

Evidence for Developing Fractional Quantum Hall States at Even Denominator1/2and1/4Fillings in Asymmetric Wide Quantum Wells

Temperature dependent symmetry to asymmetry transition in wide quantum wells

Composite fermions in a wide quantum well in the vicinity of the filling factor 1/2

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