Charge Excitations in Easy-Axis and Easy-Plane Quantum Hall Ferromagnets

Muraki, K.; Saku, T.; Hirayama, Y.

doi:10.1103/physrevlett.87.196801

Cited by 77 publications

(89 citation statements)

References 21 publications

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“…2b and 2c. This sudden drop of activation gap towards the degenerate points was observed in a wide GaAs/AlGaAs quantum well and explained within the framework of quantum Hall ferromagnetism [16].…”

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Valley splitting ofSi∕Si1−xGexheterostructures in tilted magnetic fields

Lai

Pan

et al. 2006

Phys. Rev. B

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We have investigated the valley splitting of two-dimensional electrons in high quality Si/Si1−xGex heterostructures under tilted magnetic fields. For all the samples in our study, the valley splitting at filling factor ν = 3 (∆3) is significantly different before and after the coincidence angle, at which energy levels cross at the Fermi level. On both sides of the coincidence, a linear density dependence of ∆3 on the electron density was observed, while the slope of these two configurations differs by more than a factor of two. We argue that screening of the Coulomb interaction from the low-lying filled levels, which also explains the observed spin-dependent resistivity, is responsible for the large difference of ∆3 before and after the coincidence.

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Valley splitting ofSi∕Si1−xGexheterostructures in tilted magnetic fields

Lai

Pan

et al. 2006

Phys. Rev. B

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“…Dual-subband systems realized in a quantum well have recently been studied within this context. 5,6 A similar system is the dual-subband 2DEG in a GaAs/AlGaAs heterojunction. In transport studies, the multisubband 2DEG is generally assumed to be a superposition of single 2DEGs: the Landau-level structure is a superposition of Landau fans, separated by the intersubband spacing calculated selfconsistently at zero magnetic field.…”

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Magnetization of a two-dimensional electron gas with a second filled subband

et al. 2003

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We have measured the magnetization of a dual-subband two-dimensional electron gas, confined in a GaAs/ AlGaAs heterojunction. In contrast to two-dimensional electron gases with a single subband, we observe non-1/B-periodic, triangularly shaped oscillations of the magnetization with an amplitude significantly less than 1 B * per electron. All three effects are explained by a field-dependent self-consistent model, demonstrating that the shape of the magnetization is dominated by oscillations in the confining potential. Additionally, at 1 K, we observe small oscillations at magnetic fields where Landau levels of the two different subbands cross. When an extra degree of freedom is added to a twodimensional electron gas ͑2DEG͒, many-body interactions can lead to the formation of novel electronic grounds state at the crossings of the different energy levels in the system.

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“…The single particle energy difference E z acts as effective Zeeman energy, and E a shows a slope of 5 times greater than the single particle Zeeman gap E z . This unusual behavior is likely to be caused by the easyaxis ferromagnetism [4,6]. These quantities all show an obvious change as approaching to the crossing point and demonstrate that 1/T 1 is a sensitive indicator of the pseudo-spin ferromagnetic formation.…”

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confidence: 90%

“…The disappearance and result square structure represents a pseudo-spin ferromagnet, which is due to the opening pseudo-spin gaps of easyplane or easy-axis pseudo-spin ferromagnetic states, respectively at the level crossing points of B, D and A, C, as depicted in Fig. 1b [4,5,6,9].…”

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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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Charge Excitations in Easy-Axis and Easy-Plane Quantum Hall Ferromagnets

Cited by 77 publications

References 21 publications

Valley splitting ofSi∕Si1−xGexheterostructures in tilted magnetic fields

Valley splitting ofSi∕Si1−xGexheterostructures in tilted magnetic fields

Magnetization of a two-dimensional electron gas with a second filled subband

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

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