Optically Induced Nuclear Spin Polarization in the Quantum Hall Regime: The Effect of Electron Spin Polarization through Exciton and Trion Excitations

Akiba, Kenichi; Kanasugi, Shota; Yuge, Tatsuro; Nagase, Kenzo; Hirayama, Y.

doi:10.1103/physrevlett.115.026804

Phys. Rev. Lett.

2015

DOI: 10.1103/physrevlett.115.026804

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Optically Induced Nuclear Spin Polarization in the Quantum Hall Regime: The Effect of Electron Spin Polarization through Exciton and Trion Excitations

Kenichi Akiba¹,

Shota Kanasugi

Tatsuro Yuge

et al.

Abstract: We study nuclear spin polarization in the quantum Hall regime through the optically pumped electron spin polarization in the lowest Landau level. The nuclear spin polarization is measured as a nuclear magnetic field B(N) by means of the sensitive resistive detection. We find the dependence of B(N) on the filling factor nonmonotonic. The comprehensive measurements of B(N) with the help of the circularly polarized photoluminescence measurements indicate the participation of the photoexcited complexes, i.e., the … Show more

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Cited by 4 publications

(2 citation statements)

References 24 publications

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“…The RDNMR technique depends on the current-induced dynamic nuclear polarization (DNP) that is expected to occur by transferring spin polarization from electrons to nuclei via the electron–nuclear hyperfine interaction at a domain wall (DW) separating two energetically degenerate domains12. This polarization process is in contrast to DNP by electron spin resonance1 or optical131415 pumping of intra- or inter-band transitions to generate nonequilibrium electron spin polarizations, which then polarize the nuclei via the hyperfine interaction during subsequent relaxation to equilibrium. However, the detailed mechanism is still poorly understood.…”

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confidence: 99%

Role of chiral quantum Hall edge states in nuclear spin polarization

et al. 2017

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Resistively detected NMR (RDNMR) based on dynamic nuclear polarization (DNP) in a quantum Hall ferromagnet (QHF) is a highly sensitive method for the discovery of fascinating quantum Hall phases; however, the mechanism of this DNP and, in particular, the role of quantum Hall edge states in it are unclear. Here we demonstrate the important but previously unrecognized effect of chiral edge modes on the nuclear spin polarization. A side-by-side comparison of the RDNMR signals from Hall bar and Corbino disk configurations allows us to distinguish the contributions of bulk and edge states to DNP in QHF. The unidirectional current flow along chiral edge states makes the polarization robust to thermal fluctuations at high temperatures and makes it possible to observe a reciprocity principle of the RDNMR response. These findings help us better understand complex NMR responses in QHF, which has important implications for the development of RDNMR techniques.

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Role of chiral quantum Hall edge states in nuclear spin polarization

et al. 2017

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“…Here, the two electrons in a trion form singlet and triplet spin states. The lower and higher energy peaks are respectively assigned to singlet and triplet trion peaks [20,25].…”

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Simultaneous measurement of resistively and optically detected nuclear magnetic resonance in theν=2/3fractional quantum Hall regime

2016

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We observe nuclear magnetic resonance (NMR) in the fractional quantum Hall regime at Landau level filling factor ν = 2/3 from simultaneous measurement of longitudinal resistance and photoluminescence (PL). The dynamic nuclear spin polarization is induced by applying a huge electronic current at the spin phase transition point of ν = 2/3. The NMR spectra obtained from changes in resistance and PL intensity are qualitatively the same; that is, the Knight shift (spin polarized region) and zero-shift (spin unpolarized region) resonances are observed in both. The observed change in PL intensity is interpreted as a consequence of the trion scattering induced by polarized nuclear spins. We conclude that both detection methods probe almost the same local phenomena. 71.35.Pq Quantum Hall effect has attracted a lot of physical interest since its discovery, and it has been investigated by using various kinds of experimental methods as well as other phenomena of condensed matter physics. Different experimental techniques can usually offer a good understanding of physics. However, considerable discrepancies between them occasionally arise in the quantum Hall system, even when sample preparations and experimental conditions are almost the same. For instance, the different size of skyrmion has been observed and argued [1-4]. The optical nuclear polarization observed in optical method is much larger than that in conventional and resistive methods [4][5][6][7][8][9]. The case of the electron spin polarization at Landau level filling factor ν = 5/2 is more complicated; the different experimental methods show the fully polarized state, unpolarized system, and partially polarized domains [10][11][12][13][14][15][16][17]. In these studies, the results obtained with optical methods especially exhibited controversial disagreements with other experimental methods. The possible explanation of such disagreements can be expected as follows: optically accessible phenomena can occur in the spatially limited region and/or photoexcited holes can considerably affect the system due to the Coulomb interaction.To investigate such different experimentally-observed results, the simultaneous measurement by different experimental methods is effective. In this paper, we measure the resistance and photoluminescence (PL) in the ν = 2/3 fractional quantum Hall regime simultaneously. At ν = 2/3, an electron spin phase transition (SPT) can occur due to competition between Coulomb and Zeeman energies [18], and this SPT has been observed from the resistance and PL so far [18][19][20]. Associated with the two electron spin phases (i.e., spin polarized and unpolarized states), nuclear spins are polarized when a huge electronic current is applied [18]. In the present study, the target phenomena to be simultaneously measured are this current-induced nuclear spin polarization and its nuclear magnetic resonance (NMR). This is because NMR provides local information from its spectrum [21], which has a possibility to identify the essential difference between resis...

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Evidence for a correlated phase of skyrmions observed in real space

et al. 2018

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We conduct photoluminescence microscopy that is sensitive to both electron and nuclear spin polarization to investigate the changes that occur in the magnetic ordering in the vicinity of the first integer quantum Hall state in a GaAs 2D electron system (2DES). We observe a discontinuity in the electron spin polarization and nuclear spin longitudinal relaxation time which heralds a spontaneous transition to a phase of magnetic skyrmions. We image in real space the spin phase domains that coexist at this transition, and observe hysteresis in their formation as a function of the 2DES's chemical potential. Based on measurements in a tilted magnetic field orientation, we found that the transition is protected by an energy gap containing the Zeeman energy, and conclude that the skyrmions here have formed as an ensemble.

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Optically Induced Nuclear Spin Polarization in the Quantum Hall Regime: The Effect of Electron Spin Polarization through Exciton and Trion Excitations

Cited by 4 publications

References 24 publications

Role of chiral quantum Hall edge states in nuclear spin polarization

Role of chiral quantum Hall edge states in nuclear spin polarization

Simultaneous measurement of resistively and optically detected nuclear magnetic resonance in theν=2/3fractional quantum Hall regime

Evidence for a correlated phase of skyrmions observed in real space

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