Quantum Hall effects at Landau level crossings

Hirayama, Y.; Muraki, K.; Hashimoto, Katsufumi; Takashina, Kei; Saku, T.

doi:10.1016/j.physe.2003.09.030

Cited by 5 publications

(5 citation statements)

References 23 publications

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“…Right panel: theoretical prediction using eq. (25), with the following parameters (references for the values in brackets): transverse effective mass m * = 0.19[12], mobility µ = 0.19 m 2 V −1 s −1[6], effective g-factor g * = 5[7], valley splitting in silicon E valley = 1.3 meV[13], temperatureT = 1.0 K [6], C/e = 8.6 × 10 15 m −2 V −1 [6], V off = 2.3 V [6], j y = 0.1 Am −1 [assumed].The location of the plateaus (enumerated by p) follows quantized slopes. In the transition region between two p's, the theory shows less structure compared to the experimental result.…”

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confidence: 99%

A Heuristic Quantum Theory of the Integer Quantum Hall Effect

Kramer

2006

Int. J. Mod. Phys. B

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Contrary to common belief, the current emitted by a contact embedded in a two-dimensional electron gas (2DEG) is quantized in the presence of electric and magnetic fields. This observation suggests a simple, clearly defined model for the quantum current through a Hall device that does not invoke disorder or interactions as the cause of the integer quantum Hall effect (QHE), but is based on a proper quantization of the classical electron drift motion. The theory yields a quantitative description of the breakdown of the QHE at high current densities that is in agreement with experimental data. Furthermore, several of its key points are in line with recent findings of experiments that address the dependency of the QHE on the 2DEG bias voltage, results that are not easily explained within the framework of conventional QHE models. PACS: 73.43.Cd: Quantum Hall effects: Theory and modeling 1 Open problems in the quantum Hall effect.Despite more than 25 years of effort to understand the nature of the quantum Hall effect (QHE), no comprehensive theoretical description emerged that is unanimously accepted. For instance, von Klitzing et. al recently remarked: "[The edge-channel model of Büttiker] is widely used in textbooks on the integer QHE. We don't want to discuss it here, since recent experimental observations of the current distribution point to a somewhat different microscopic picture of the QHE." ([1], p. 41. Translation by the author, the experiment Klitzing refers to is [30]). Unsolved problems remain, in particular the origin of the breakdown of the QHE at high current densities and thus large electric Hall fields.

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confidence: 99%

A Heuristic Quantum Theory of the Integer Quantum Hall Effect

Kramer

2006

Int. J. Mod. Phys. B

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“…It is possible that the partially polarized ground states ) , Moreover, the DNP can be suppressed by the mobility of domains, which is expected to be different at different LL intersections. 29 In conclusion, we have successfully demonstrated DNP and RDNMR in a single InSb 2DEG. and R xx decayed to the original value.…”

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confidence: 70%

Dynamic nuclear polarization and nuclear magnetic resonance in the simplest pseudospin quantum Hall ferromagnet

Liu

Yang²,

Mıshıma

et al. 2010

Phys. Rev. B

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We present dynamic nuclear polarization (DNP) in the simplest pseudospin quantum Hall ferromagnet (QHF) of an InSb two-dimensional electron gas with a large g factor using tilted magnetic fields. The DNP-induced amplitude change of a resistance spike of the QHF at large current enables observation of the resistively detected nuclear magnetic resonance of the high nuclear spin isotope 115 In with nine quadrupole splittings. Our results demonstrate the importance of domain structures in the DNP process.The nuclear spin relaxation time T 1 in this QHF was relatively short (~ 120 s), and almost temperature independent.

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“…Since the two points have equivalent LLs crossing configurations, one would expect that they are the same easy-axis QHPF states and should produce similar NMR responses. In principle, the NMR signal can be suppressed by spin-orbital coupling [21] or mobility of domains [22]. However, in our case, point A and C have identical strength in spin-orbital coupling and disorder.…”

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confidence: 74%

Probing a quantum Hall pseudospin ferromagnet by resistively detected nuclear magnetic resonance

Guo

Hao

et al. 2010

Phys. Rev. B

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Resistively Detected Nuclear Magnetic Resonance (RD-NMR) has been used to investigate a twosubband electron system in a regime where quantum Hall pseudo-spin ferromagnetic (QHPF) states are prominently developed. It reveals that the easy-axis QHPF state around the total filling factor ν = 4 can be detected by the RD-NMR measurement. Approaching one of the Landau level (LL) crossing points, the RD-NMR signal strength and the nuclear spin relaxation rate 1/T1 enhance significantly, a signature of low energy spin excitations. However, the RD-NMR signal at another identical LL crossing point is surprisingly missing which presents a puzzle.PACS numbers: 73.43. Nq, 71.30.+h, 72.20.My The multi-component electron systems have been continuously drawing intensive research interest because of its novel ground states and excitations [1]. In experimental systems, different Landau levels (LLs) can be tuned to cross by varying gate voltage, charge density, magnetic field or the magnetic field tilted angle to the sample. Electron-electron correlations become particularly prominent when two or more sets of LLs with different layer, subband, valley, spin, or Landau level indices are brought into degeneracy [1,2,3,4,5,6,7,8]. Recent experiments in single quantum well with two subbands occupied systems [5,6], showed evidence of the formation of quantum Hall pseudospin ferromagnets (QHPFs) due to the interactions of the two subbands (termed as pseudospins) around the LLs crossing point. The QHPFs taking place at total filling factor ν = 3, 5 and ν = 4 are easy-plane or easy-axis QHPFs respectively, depending on the details of the two subbands configurations. In spite of various theoretical models [9,10,11] motivated by these findings, a comprehensive understanding is not yet achieved. Thus far, experimental and theoretical studies all focused on the pseudospin freedom. However, in this work we would address the unique spin excitations in the QHPF states.To address the question whether spin states in twosubband systems in nature, measurements other than the conventional transport and optical means are needed. Since the Zeeman energy of nuclear spin is about 3 orders of magnitude smaller than that of electron spin, exchange of spin angular momentum between the electron and nuclear spin is allowed only when the electron system supports spin excitations with low energy. The nuclear spin relaxation rate 1/T 1 thus probes the density of states at low energy of the electron spin system that cannot be accessed by other means. The resistively detected NMR technique has recently emerged as an effective method to probe collective spin states in the fractional quantum Hall regime [12,13], the Skyrmion spin texture close to the filling factor 1 [14,15], the role of electron spin polarization in the phase transition of a bilayer system [16,17], and the ferromagnetic state accompanied by collective spin excitations of a two-subband system [18]. Here we use this technique to study spin freedom and its relation with pseudospin in the vicinity of...

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Quantum Hall effects at Landau level crossings

Cited by 5 publications

References 23 publications

A Heuristic Quantum Theory of the Integer Quantum Hall Effect

A Heuristic Quantum Theory of the Integer Quantum Hall Effect

Dynamic nuclear polarization and nuclear magnetic resonance in the simplest pseudospin quantum Hall ferromagnet

Probing a quantum Hall pseudospin ferromagnet by resistively detected nuclear magnetic resonance

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