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Khrapai, V. S.; Shashkin, A. A.; Shangina, E. L.; Pellegrini, Vittorio; Beltram, Fabio; Biasiol, G.; Sorba, L.

doi:10.1103/physrevb.72.035344

Cited by 24 publications

(13 citation statements)

References 24 publications

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“…The linear dependence of ǻ on B is qualitatively different from what is expected for QHF, which predicts 21 a gap that scales as B 1/2 . It is worth noting, however, that early studies 36,37 of the exchange-enhanced spin gap at Ȟ = 1 in GaAs samples also showed an energy gap that was linear in B. QHF predicts 21 ǻ ~ 100 meV for magnetic fields of a few Tesla, far larger than we observe, but this discrepancy is likely due to disorder in our samples.…”

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confidence: 77%

Broken-symmetry states and divergent resistance in suspended bilayer graphene

2009

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The |Ȟ| = 2 states emerge at B = 0.7 T, and all symmetries are broken for B 3 T.We focus first on the behavior of our samples in zero magnetic field. Fig. 1c shows the resistivity ȡ of two suspended bilayers as a function of carrier density n. Each sample displays a sharp peak in ȡ with a full width at half maximum on the order of 10 10 cm -2 , comparable to suspended monolayer devices 5,6 and an order of magnitude smaller than unsuspended bilayers 27 .In all samples, the peak lies close to zero back gate voltage (|V peak | < 0.5 V), indicating that there is little extrinsic doping in our devices. As a measure of sample cleanliness, we can estimate the magnitude of carrier density fluctuations įn based on the carrier density dependence of the conductivity ı(n), shown in Fig. 1d. Near the charge neutrality point, local variations in 4 potential lead to the formation of electron-hole puddles 28 , and ı(n) is expected 29 to remain constant in this regime because |n| < įn. In our suspended bilayers, įn is typically on the order of 10 10 cm -2 , and it reaches as low as 10 9 cm -2 in sample S3.The temperature dependence of the minimum conductivity ı min (Fig. 1e) (m e is the electron mass). In sample S3, ı min shows temperature dependence down to 450 mK, providing an upper bound of įn < 10 9 cm -2 . In contrast, ı min saturates at approximately 2 K in sample S4, corresponding to įn § 5x10 9 cm -2 . Both estimates are consistent with the estimate of disorder obtained from ı(n). In both samples, ı min at 450 mK is a few times the conductance quantum, in good agreement with theoretical predictions for its intrinsic limit [30][31][32] .In contrast to the typically reported linear behavior in bilayer graphene, ı(n) is sublinear in suspended samples (Fig. 1f). If we assume mobility μ = (1/e)dı/dn, then μ typically ranges from 10,000-15,000 cm 2 /V·s in our suspended bilayers at carrier density n of 2-3x10 11 cm -2 .These numbers represent a modest improvement of approximately a factor of two over unsuspended bilayers, but it remains unclear why the mobility is this low given the indications of sample quality discussed above, the low magnetic field at which we observe quantum Hall plateaus, and the high mobilities observed in suspended monolayers 5,6 . Adam and Das Sarma predict 29 that the mobility of bilayer graphene should be more than an order of magnitude smaller than that of monolayer graphene. This discrepancy was not observed in unsuspended 5 samples 27 , but mobility in such samples may be limited by disorder associated with the substrate.It is also worthwhile to comment on the possibility that the sharp dip in conductivity at low n is enhanced by a small energy gap that opens due to disorder-induced differences in carrier density between the top and bottom layers of the flake 21 . Differences in density of a few times 10 9 cm -2 would lead to an energy gap 26 of approximately 0.3 meV.We next discuss the magnetic field dependent behavior of our samples. Figs. 2a and 2b show the conductance of sample S1 as a functi...

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confidence: 77%

Broken-symmetry states and divergent resistance in suspended bilayer graphene

2009

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“…26 However, the skyrmion at ν = 3 is fragile and it was found that Landau-level mixing tends to favor spinpolarized quasiparticles. 27 It was indicated that the lowestlying charged excitations at ν = 3 was accompanied with a single spin flip at B 2 T. 28 Depolarization of the degree of circular polarization of the PL P = (I σ − − I σ + )/(I σ − + I σ + ) is expected at ν > 3 and at ν < 3 for the skyrmion ground state. The PL intensities at around ν = 3 in Fig.…”

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confidence: 99%

Exchange energy enhancedg-factors obtained from Landau fan diagrams at low magnetic fields

et al. 2013

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We report on measurement of the electron-hole effective g-factors (g * eff ) depending on electron filling factors ν from magnetophotoluminescence spectroscopy at low magnetic fields B < 1 T in low electron density regime in a GaAs/Al 0.33 Ga 0.67 As-gated quantum well. Enhancement of g * eff at odd ν is observed. The oscillatory behavior of g * eff is compared with results of a theory that takes into account the lowest-order exchange interaction of the screened Coulomb interaction. Good agreement of the observed g * eff with theoretical results is obtained except ν at around 3. The enhancement of g * eff at even ν with decrease in electron density has not been observed.

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“…The exchange energy of a single spin-flip excitation is supposed to be responsible for a serious enhancement of the excitation energy in comparison to the single-particle Zeeman splitting [2][3][4][5] . This enhancement is sensitive 2 to the excitation wave vector k. It is widely accepted, that in transport experiments 3,4,6,7 k = ∞ excitations are tested, while optical investigations 5 allow to probe excitations at different k. In low magnetic fields, the possibility of complicated spin textures (skyrmions) formation is still debated 6,7 .…”

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Local investigation of the energy gap within the incompressible strip in the quantum Hall regime

et al. 2010

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We experimentally study the energy gap within the incompressible strip at local filling factor νc = 1 at the quantum Hall edge for samples of very different mobilities. The obtained results indicate strong enhancement of the energy gap in comparison to the single-particle Zeeman splitting. We identify the measured gap as a mobility gap, so a pronounced experimental in-plane magnetic field dependence can both be attributed to the spin effects as well as to the change in the energy levels broadening.

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Spin gap in the two-dimensional electron system ofGaAs∕AlxGa1−xAssi

Cited by 24 publications

References 24 publications

Broken-symmetry states and divergent resistance in suspended bilayer graphene

Broken-symmetry states and divergent resistance in suspended bilayer graphene

Exchange energy enhancedg-factors obtained from Landau fan diagrams at low magnetic fields

Local investigation of the energy gap within the incompressible strip in the quantum Hall regime

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