Quantum Hall Ferromagnetism in a Two-Dimensional Electron System

Eom, Jonghwa; Cho, Hyun-Ick; Kang, W.; Campman, K. L.; Gossard, A. C.; Bichler, Max; Wegscheider, Werner

doi:10.1126/science.289.5488.2320

Cited by 72 publications

(72 citation statements)

References 31 publications

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“…Experimental observations of hysteresis in the transport properties of two-dimensional electron gas (2DEG) made of single layer and double layer quantum well heterostructures used in the study of the integer and fractional quantum Hall effects have been widely reported [1][2][3][4][5][6][7]. In the double-layer structure, the origin of the hysteresis was attributed to a phase transition between oppositely polarized ground states localized in the different layers [1].…”

Section: Introductionmentioning

confidence: 99%

Hysteresis in the conductance of asymmetrically biased GaAs quantum point contacts with in-plane side gates

Bhandari

Dutta

Charles

et al. 2013

Journal of Applied Physics

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We have observed hysteresis between the forward and reverse sweeps of a common mode bias applied to the two in-plane side gates of an asymmetrically biased GaAs quantum point contact (QPC). The size of the hysteresis loop increases with the amount of bias asymmetry ΔV g between the two side gates and depends on the polarity of ΔV g . Our results are in qualitative agreement with Non-Equilibrium Green's Function simulations including the effects of dangling bond scattering on the sidewalls of the QPC. It is argued that hysteresis may constitute another indirect proof of spontaneous spin polarization in the narrow portion of the QPC.2

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Section: Introductionmentioning

confidence: 99%

Hysteresis in the conductance of asymmetrically biased GaAs quantum point contacts with in-plane side gates

Bhandari

Dutta

Charles

et al. 2013

Journal of Applied Physics

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“…They are common magnetic materials, and often indicate a non-equilibrium situation associated with a phase transition and the presence of domains [1]. Recently, hysteresis has also been reported in various two-dimensional (2D) carrier systems in semiconductor structures at low temperatures and high magnetic fields [2,3,4,5,6,7]. In these cases, magneto-resistance (ρ xx ) hysteresis appears in the quantum Hall (QH) regime when two Landau levels (LLs) with opposite spin are brought into coincidence.…”

mentioning

confidence: 99%

Layer-charge instability in unbalanced bilayer systems in the quantum Hall regime

et al. 2003

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Measurements in GaAs hole bilayers with unequal layer densities reveal a pronounced magnetoresistance hysteresis at the magnetic field positions where either the majority or minority layer is at Landau level filling factor one. At a fixed field in the hysteretic regions, the resistance exhibits an unusual time dependence, consisting of random, bidirectional jumps followed by slow relaxations. These anomalies are apparently caused by instabilities in the charge distribution of the two layers.PACS numbers: 71.70.Ej, 73.43.Qt Hysteretic phenomena are widespread in nature. They are common magnetic materials, and often indicate a non-equilibrium situation associated with a phase transition and the presence of domains [1]. Recently, hysteresis has also been reported in various two-dimensional (2D) carrier systems in semiconductor structures at low temperatures and high magnetic fields [2,3,4,5,6,7]. In these cases, magneto-resistance (ρ xx ) hysteresis appears in the quantum Hall (QH) regime when two Landau levels (LLs) with opposite spin are brought into coincidence. While the 2D systems studied have been notably different, the common thread in these experiments is that there is a magnetic transition involving the carrier spin [8].Here we present hysteretic ρ xx data in 2D bilayer systems in the QH regime. The hysteresis in these systems has a different origin and is caused by a non-equilibrium charge distribution in the two layers. We studied the magneto-transport coefficients of GaAs bilayer hole systems with unequal layer densities. When the interlayer tunneling is sufficiently small, ρ xx of the bilayer system exhibits a pronounced hysteresis at perpendicular magnetic field (B) positions close to where either the majority or minority layer is at LL filling factor one. Most remarkable is the time dependence of ρ xx at a fixed field in the hysteretic regime, when the two layers are closely spaced. As a function of time, ρ xx exhibits large, random, sudden jumps toward higher and lower values, followed by a slow decay in the opposite direction. The data may signal an instability in the charge distribution of the two layers, i.e., an instability associated with the pseudospin (layer), rather than spin, degree of freedom.We studied nine GaAs bilayer hole samples from six different wafers, all grown on GaAs (311)A substrates and modulation doped with Si. In all samples, the holes are confined to two 15nm-wide GaAs quantum wells which are separated by AlAs or AlAs/AlGaAs barriers with thickness 7.5 ≤ W ≤ 200nm. The rather thick barrier combined with the large effective mass of GaAs 2D holes [9] reduces considerably the tunneling between the two layers [10]. As grown, the samples have layer densities of ≤ 7 × 10 10 cm −2 , and low temperature (T ) mobilities of ∼ 35 m 2 /Vs. Metallic top and bottom gates were added to control the densities in the layers. We studied several types of devices, including 2.5×2.5mm square samples and ones with patterned Hall bars; in these samples the ohmic contacts contact both layers. ...

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“…This quantum Hall ferromagnetism manifests itself in transport experiments by the appearance of hysteretic behavior as well as Barkhausen jumps in the sample resistance [7,8]. Also a coexistence of unpolarized and polarized spin domains has been found by nuclear magnetic resonance spectroscopy [9].…”

Section: The Electron Spin System In the Quantum Hall Effectmentioning

confidence: 97%

“…However, when taking a deeper look into quantum Hall physics, the importance of spin related phenomena becomes evident. Today, many interesting spin phenomena are known to exist, such as spin transitions of FQHS [8,160,161], ferromagnetic spin ordering [7,8,162,163] and skyrmionic spin excitations [10,11]. The spin degree of freedom enriches the quantum Hall physics in many regards.…”

Section: Chaptermentioning

confidence: 99%

“…By tuning the relative strength of both energies, transitions between the respective spin phases can be induced. These spin transitions are accompanied by the occurrence of ferromagnetic domains [7][8][9]. Even in the absence of the fractional quantum Hall effect, complex spin structures do exist such as skyrmionic spin formations around filling factor = 1 [10,11] and a spatially ordered spin density in the regime of the density modulated phases.…”

Section: Introductionmentioning

confidence: 99%

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