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Dobers, M.; Klitzing, K. von; Weimann, G.

doi:10.1103/physrevb.38.5453

Cited by 242 publications

(130 citation statements)

References 14 publications

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“…Here we plot the dependence of E c = αe 2 /ǫl B and E z = gµ B B versus B-field with l B = (hc/eB) 1/2 being the magnetic length, ǫ = 12.9 the dielectric constant of GaAs, and µ B the Bohr magneton. We use g = 0.44 for the g-factor in GaAs [32] and α = 0.02 from a numerical calculation of Morf [10]. For a spin-unpolarized state one would take the energy gap to be ∆ = E c − E z which is represented by the difference between E c and E z in Fig.…”

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confidence: 99%

Experimental evidence for a spin-polarized ground state in the ν=5/2 fractional quantum Hall effect

Pan

Störmer

Tsui

et al. 2001

Solid State Communications

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We study the ν = 5/2 even-denominator fractional quantum Hall effect (FQHE) over a wide range of magnetic field in a heterojunction insulated gate field-effect transistor (HIGFET). The electron density can be tuned from n = 0 to 7.6 × 10 11 cm −2 with a peak mobility µ = 5.5 × 10 6 cm 2 /Vs. The ν = 5/2 state shows a strong minimum in diagonal resistance and a developing Hall plateau at magnetic fields (B) as high as 12.6T. The strength of the energy gap varies smoothly with B-field. We interpret these observations as strong evidence for a spin-polarized ground state at ν = 5/2. Eisenstein et al.[4] tested the spin-polarization of the ν = 5/2 state by tilted magnetic field experiments [5] in a traditional, fixed-density sample. While the orbital motion of the electrons and hence their correlation energy (E c ) is subject only to the perpendicular component of the magnetic (B) field, the Zeeman energy (E z ) depends on the total B-field. Varying angle and B-field, the specimen can be kept in the ν = 5/2 state while the Zeeman energy is raised. Such a procedure should leave a spinpolarized state intact, but should be detrimental to a spin-unpolarized state, once the Zeeman energy cost surmounts the gain in correlation energy. In the experiment the strength of the ν = 5/2 state decreased quickly upon tilting and the state disappeared totally at θ ∼ 50 • . This was taken as evidence of a spin-singlet state at ν = 5/2.In recent years, with the advent of the composite fermion (CF) model [6,7], there has been a renewed interest in the ν = 5/2 state [8][9][10][11][12][13][14][15][16][17][18][19]. Moore and Read (MR) proposed a ground state of p-wave paired CF's [8]. Unlike the HR state, the MR state is spin-polarized. It is now being argued that the earlier disappearance of the ν = 5/2 state under tilt may be the result of the compression of the wave function due to the in-plane component of the B-field. This reduction of the z-extend of the wave function affects electron correlation and is the cause for the gap collapse, rather than the suspected increase in Zeeman energy. Indeed, recently two tilted field experiments [20,21] showed that the added in-plane magnetic field not only destroys the FQHE at ν = 5/2 but also induces an electronic transport anisotropy. Theoretical modeling [22] suggests that this is due to a phase transition from the MR pairing state to an anisotropic state and unrelated to any spin-effect. Hence, the spinpolarization of the ν = 5/2 FQHE remains unresolved and there is presently little experimental input into the debate over the nature of the even-denominator FQHE state.Here we pursue the spin-polarization of the ν = 5/2 state in analogy to the tilted field experiments by investigating the competition between E c and E z . Rather than tuning their ratio in a fixed density specimen by tilt, we keep the B-field perpendicular to the 2DES and employ a variable density specimen. Since for a fixed filling factor, such as ν = 5/2, E c ∝ n 1/2 , whereas E z ∝ n, increasing electron density modifies the...

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confidence: 99%

Experimental evidence for a spin-polarized ground state in the ν=5/2 fractional quantum Hall effect

Pan

Störmer

Tsui

et al. 2001

Solid State Communications

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“…21 The dashed straight line represents the Larmor energy taking for g * the Any sensible comparison with these results must take into account the B dependence of g * . This dependence has been clearly established in magnetoresistivity experiments, 24 taking advantage of the fact that the electric-spin resonance affects the magnetoresistivity of the 2D electron gas, and this can be used to determine g * ͑B͒. These experiments probe the one-electron energy levels and are not influenced by manyelectron interactions, contrarily to magnetoquantum oscillations, which are strongly influenced by many-electron interactions.…”

Section: Comparison With Experiments and Discussionmentioning

confidence: 99%

“…24 in conjunction with Eq. ͑17͒, to establish a clear evidence of spin-orbit effects on the ⑀ S energy obtained from resonant inelastic light scattering experiments, and have satisfied ourselves with the more limited scope of using Eq.…”

Section: Comparison With Experiments and Discussionmentioning

confidence: 99%

“…We extend here this study to the influence on the Larmor resonance of the combined effect of both Dresselhaus 18 and Bychkov-Rashba 19,20 SO interactions, and use our results to discuss some features of the spin modes disclosed by inelastic light scattering 21,22 and electron-spin resonance experiments. 23,24 Our approach is based on the solution of the equation of motion up to second order in the SO intensity parameters. 17 This method has been also used to derive the Kohn theorem, 25 and goes as follows.…”

Section: Introductionmentioning

confidence: 99%

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Spin-orbit effects on the Larmor dispersion relation in GaAs quantum wells

et al. 2006

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We have studied the relevance of spin-orbit coupling to the dispersion relation of the Larmor resonance observed in inelastic light scattering and electron-spin resonance experiments on GaAs quantum wells. We show that the spin-orbit interaction, here described by a sum of Dresselhaus and Bychkov-Rashba terms, couples Zeeman and spin-density excitations. We have evaluated its contribution to the spin splitting as a function of the magnetic field B, and have found that in the small B limit, the spin-orbit interaction does not contribute to the spin splitting, whereas at high magnetic fields it yields a B independent contribution to the spin splitting given by 2͑ R 2 − D 2 ͒, with R,D being the intensity of the Bychkov-Rashba and Dresselhaus spin-orbit terms.

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“…A similar statement also holds for spin-excitons, intra-Landau level spin-flip excitations. In a system with rotational invariance in spin space, Larmor's theorem [3] dictates that Coulomb interactions do not contribute to the energy of zeromomentum spin-excitons. In contrast to these magnetoplasma and spin-exciton excitations, there exist no symmetry arguments which restrict the energy of the combined zero momentum cyclotron spin-flip mode (CSFM).…”

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Cyclotron spin-flip mode as the lowest-energy excitation of unpolarized integer quantum Hall states

et al. 2005

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The cyclotron spin-flip modes of spin unpolarized integer quantum Hall states (ν = 2, 4, 6) have been studied with inelastic light scattering. The energy of these modes is significantly smaller compared to the bare cyclotron gap. Second order exchange corrections are held responsible for a negative energy contribution and render these modes the lowest energy excitations of unpolarized integer quantum Hall states.PACS numbers: 73.43. Lp, 75.30.Ds, 71.70.Ej According to Kohn's theorem [1], homogenous electromagnetic radiation incident on a translationally invariant electron system can only couple to the center-of-mass coordinate. Such radiation is unable to excite internal degrees of freedom associated with the Coulomb interaction. As a result, physical phenomena originating from electron-electron interactions leave the cyclotron resonance unaffected. Hence, spin-unperturbed magnetoplasmons excited under these conditions have an energy equal to the bare cyclotron energy, irrespective of existing electron-electron correlations [2]. A similar statement also holds for spin-excitons, intra-Landau level spin-flip excitations. In a system with rotational invariance in spin space, Larmor's theorem [3] dictates that Coulomb interactions do not contribute to the energy of zeromomentum spin-excitons. In contrast to these magnetoplasma and spin-exciton excitations, there exist no symmetry arguments which restrict the energy of the combined zero momentum cyclotron spin-flip mode (CSFM). It is well established that the cyclotron-spin-flip mode excited from spin-polarized ground states acquires considerable exchange energy even for zero momentum [4,5,6]. The energy of this mode may thus serve as a unique probe of many-body interactions in the electronic system. Hitherto, it has not been considered that there is also an exchange contribution to the energy of the zero momentum cyclotron-spin-flip modes of unpolarized quantum Hall ground states at even integer fillings (ν = 2, 4, 6, . . .). First order perturbation calculations in the ratio r c = E C /hω c explicitly predicted a zero exchange contribution to the total energy of this combined mode of unpolarized quantum Hall ground states [2] (E C is the characteristic Coulomb energy scale andhω c the cyclotron energy). Here, we experimentally demonstrate however that the energy of these modes is considerably reduced compared with the bare cyclotron gap. We corroborate with theoretical considerations that the negative energy contribution arises from second order Coulomb corrections and so was not captured by previous first order perturbation calculations.Two high-quality heterostructures were studied. Each consisted of a single-side modulation doped 30 nm AlGaAs/GaAs quantum well (QW) with an electron density between 1 and 1.2 · 10 11 cm −2 and a mobility of 5 − 7 · 10 6 cm 2 /(Vs). The density n s was tuned continuously via the opto-depletion effect and was measured with luminescence [7]. Inelastic light scattering (ILS) spectra were recorded at 1.5 K in the back-scattering geo...

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Electron-spin resonance in the two-dimensional electron gas of GaAs-AlxGa1

Cited by 242 publications

References 14 publications

Experimental evidence for a spin-polarized ground state in the ν=5/2 fractional quantum Hall effect

Experimental evidence for a spin-polarized ground state in the ν=5/2 fractional quantum Hall effect

Spin-orbit effects on the Larmor dispersion relation in GaAs quantum wells

Cyclotron spin-flip mode as the lowest-energy excitation of unpolarized integer quantum Hall states

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