Observation of extremely slow hole spin relaxation in self-assembled quantum dots

Heiss, D.; Schaeck, S.; Huebl, Hans; Bichler, Max; Abstreiter, G.; Finley, Jonathan J.; Bulaev, D. V.; Loss, Daniel

doi:10.1103/physrevb.76.241306

Cited by 208 publications

(209 citation statements)

References 23 publications

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“…2a for GaAs quantum dot A1. It can be seen that the dependences for both Ga and As are linear as predicted by equations (1) and (2). Fitting gives the following values for the hole hyperfine constants γ Ga = −7.0±4.0% and γ As = +15.0 ± 4.5%.…”

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confidence: 60%

Element-sensitive measurement of the hole–nuclear spin interaction in quantum dots

et al. 2012

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It has been proposed that valence-band holes can form robust spin qubits 1-4 owing to their weaker hyperfine coupling compared with electrons 5,6 . However, it was demonstrated recently 7-11 that the hole hyperfine interaction is not negligible, although a consistent picture of the mechanism controlling its magnitude is still lacking. Here we address this problem by measuring the hole hyperfine constant independently for each chemical element in InGaAs/GaAs, InP/GaInP and GaAs/AlGaAs quantum dots. Contrary to existing models 10,11 we find that the hole hyperfine constant has opposite signs for cations and anions and ranges from −15% to +15% relative to that for electrons. We attribute such changes to the competing positive contributions of p-symmetry atomic orbitals and the negative contributions of d-orbitals. These findings yield information on the orbital composition of the valence band 12 and enable a fundamentally new approach for verification of computed Bloch wavefunctions in semiconductor nanostructures 13 . Furthermore, we show that the contribution of cationic d-orbitals leads to a new mechanism of hole spin decoherence.Owing to the s-type character of the Bloch wavefunction, the hyperfine interaction of the conduction band electrons is isotropic (the Fermi contact interaction) and is described by a single hyperfine constant A, positive (A > 0) for most III-V semiconductors and proportional to the electron density at the nucleus. In contrast, for valence-band holes the contact interaction vanishes owing to the symmetry properties of the wavefunction, and the non-local dipole-dipole interaction dominates 10,11,[13][14][15] . As a result, the sign, magnitude and anisotropy of the hyperfine interaction depend on the actual form of the valence-band Bloch wavefunction, which is usually not available with sufficient precision. Thus, predicting the properties of the hole hyperfine coupling using first-principle calculations remains a difficult task.In this work we perform direct measurements of the hyperfine constants that describe the hole hyperfine interaction with nuclear spins polarized along the growth axis of the structure (that is, the diagonal elements of the hole hyperfine Hamiltonian). This is achieved by simultaneous and independent detection of the electron and hole Overhauser shifts using high-resolution photoluminescence spectroscopy of neutral quantum dots. In contrast to previous work 9 , we now also apply excitation with a radiofrequency oscillating magnetic field, which allows isotopeselective probing of the valence-band hole hyperfine interaction 16 . Using this technique we find that in all studied materials, cations (gallium, indium) have a negative hole hyperfine constant, whereas it is positive for anions (phosphorus, arsenic), a result attributed to the previously disregarded contribution of the cationic d-shells into the valence-band Bloch wavefunctions.Using the experimentally measured diagonal components of the hyperfine Hamiltonian (hole hyperfine constants) we calculate its non-di...

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confidence: 60%

Element-sensitive measurement of the hole–nuclear spin interaction in quantum dots

et al. 2012

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“…However, if the precession interval is approximately a multiple of all Unlike electrons having s-type atomic wavefunctions, the hole has a wavefunction constructed predominantly from p-orbitals with zero density at the nuclear site. This leads to a vanishing contact part of the HI, which combined with extended hole spin life-times in QDs 81 presents holes as a potentially viable alternative to electrons for implementation of spin qubits 81,82 . Recent theory predicts that the hole HI, dipole-dipole in nature, can be as large as 10% of that of the electron, and is strongly anisotropic [83][84][85][86] .…”

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confidence: 99%

Nuclear spin effects in semiconductor quantum dots

et al. 2013

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“…That is why the electron spin relaxation and decoherence sources in QDs have been intensively studied in the last few years; some more limited number of studies have centered on the hole spin. The main conclusions of these studies are that in moderate magnetic fields (1-10 T) and at low temperature, the electron T e 1 and the hole T h 1 spin-relaxation times are governed by the same mechanism, i.e., the spin-orbitmediated single-phonon scattering, [4][5][6][7][8] which leads to relatively slow relaxation times in the range of milliseconds [9][10][11][12][13] with T h 1 five or ten times smaller than T e 1 . 12 However, the electron-and hole-spin coherence times T e,h 2 have been found to be in the microsecond range up to 15 K, [14][15][16][17] and for higher temperatures T e 2 has shown a sharp decrease 16 related to the modulation by phonons of the hyperfine (hf) interaction with the random fluctuating host nuclear spins.…”

Section: Introductionmentioning

confidence: 97%

Hole-spin initialization and relaxation times in InAs/GaAs quantum dots

et al. 2011

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We study, at low temperature and zero magnetic field, the hole-spin dynamics in InAs/GaAs quantum dots. We measure the hole-spin relaxation time at a time scale longer than the dephasing time (about ten nanoseconds), imposed by the hole-nuclear hyperfine coupling. We use a pump-probe configuration and compare two experimental techniques based on differential absorption. The first one works in the time domain, and the second one is a new experimental method, the dark-bright time-scanning spectroscopy (DTS), working in the frequency domain. The measured hole-spin relaxation times, using these two techniques, are very similar, in the order of T h N ≈1 μs. It is mainly imposed by the inhomogeneous hole hyperfine coupling in the hole localization volume. The DTS technique allows us also to measure the hole-spin initialization time τ i . The hole spin is initialized by a periodic train of circularly polarized pulses at 76 MHz; we have observed that τ i decreases as the power density increases, and we have measured a minimum value of τ i ≈100 ns in good agreement with a simple model [seeB. Eble, P. Desfonds, F. Fras, F. Bernardot, C. Testelin, M. Chamarro, A. Miard, and A. Lemaître, Phys. Rev. B 81, 045322 (2010)].

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Observation of extremely slow hole spin relaxation in self-assembled quantum dots

Cited by 208 publications

References 23 publications

Element-sensitive measurement of the hole–nuclear spin interaction in quantum dots

Element-sensitive measurement of the hole–nuclear spin interaction in quantum dots

Nuclear spin effects in semiconductor quantum dots

Hole-spin initialization and relaxation times in InAs/GaAs quantum dots

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