Zero-field spin quantum beats in charged quantum dots

Kozin, I. E.; Davydov, V. G.; Ignatiev, I. V.; Kavokin, Alexey; Kavokin, K. V.; Malpuech, Guillaume; Ren, Hongwen; Sugisaki, Mitsuru; Sugou, S.; Masumoto, Yasuaki

doi:10.1103/physrevb.65.241312

Cited by 69 publications

(54 citation statements)

References 19 publications

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“…Because the lowest electron level in the QDs is close to the Fermi level of the doped substrate, the external electric bias allowed us to control the charged state of the QDs in the sample. 13 As is decribed later, a trionic quantum beat measurement showed that there is, on average, one doped electron per dot under a bias of U = −0.1 V. 13 Under positive bias, QDs doped with more than two electrons become dominant, while neutral QDs become dominant below the electric bias of U = −0.4 V, where an excitonic quantum beat was clearly observed. 29 A continous-wave Ti:sapphire laser was used for the quasiresonant excitation of InP QDs in the Hanle measurements.…”

Section: Methodsmentioning

confidence: 99%

“…Observation of a trionic quantum beat ensures the presence of a single doped electron in a QD. 13 Because of the longest spin-dephasing time and the exact coincidence of the sharpest Hanle dip with the trionic quantum beat, the sharpest Lorentzian was assigned to the spin-dephasing relaxation of the doped electron. The half-width of the sharpest Lorentzian B 1 = 4.6 mT gives the scaled spin-dephasing time ͑gT 2 * = 2.5 ns͒ of the doped electrons.…”

Section: B the Hanle Curve In Single-electron-doped Quantum Dotsmentioning

confidence: 99%

“…In the case of charge-tunable QDs particularly, we can control the charge state in the QDs with an applied electric bias. 12,13 From this point of view, the spins of doped electrons or holes in the charged QDs are an attractive research target. The long spin relaxation time T 1 of doped electrons and holes has been reported in several publications.…”

Section: Introductionmentioning

confidence: 99%

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Spin dephasing of doped electrons in charge-tunable InP quantum dots: Hanle-effect measurements

et al. 2006

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The spin dephasing relaxation in single-electron-doped InP quantum dots was studied by means of Hanle measurements. When an InP quantum dot is doped with one electron on average, a narrow Lorentzian dip with half-width of 4.6 mT appeared and was superposed on two Lorentzians with half-widths of 1.54 and 128 mT in the Hanle curve. The half-widths 1.54 T, 128 mT, and 4.6 mT are ascribed to spin-dephasing relaxation of holes, electron-hole pairs, and doped electrons consistuting negative trions, respectively. The corresponding spin coherence time of the doped electrons at 5 K is 1.7 ns, which is determined by the frozen fluctuation of nuclear spins in the quantum dots. With increase of temperature, the spin-dephasing rate of the doped electrons increases.

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Section: Methodsmentioning

confidence: 99%

Section: B the Hanle Curve In Single-electron-doped Quantum Dotsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Spin dephasing of doped electrons in charge-tunable InP quantum dots: Hanle-effect measurements

et al. 2006

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“…Semi-transparent indiumtin-oxide electrode is deposited on top of the sample to control the charge state of the QDs by means of an applied electric bias. 5,6,17 For the present study on the singly negatively charged QDs we apply an electric bias of U b = −0.1 V. This is because it was found from a previous study of trionic quantum beats 17 on the same sample that at U b ≈ −0.1 V the QDs contain one resident electron per dot, on an average.…”

Section: Methodsmentioning

confidence: 99%

Nuclear-spin effects in singly negatively charged InP quantum dots

et al. 2007

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Experimental investigation of nuclear spin effects on the electron spin polarization in singly negatively charged InP quantum dots is reported. Pump-probe photoluminescence measurements of electron spin relaxation in the microsecond timescale are used to estimate the time-period TN of the Larmor precession of nuclear spins in the hyperfine field of electrons. We find TN to be ∼ 1 µs at T ≈ 5 K, under the vanishing external magnetic field. From the time-integrated measurements of electron spin polarization as a function of a longitudinally applied magnetic field at T ≈ 5 K, we find that the Overhauser field appearing due to the dynamic nuclear polarization increases linearly with the excitation power, though its magnitude remains smaller than 10 mT up to the highest excitation power (50 mW) used in these experiments. The effective magnetic field of the frozen fluctuations of nuclear spins is found to be 15 mT, independent of the excitation power.

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“…Since this doping density corresponds to ∼ 20 free carriers per QD, the QDs are highly charged, in contrast to previous measurements of spin dynamics in -QDs with a single extra electron. 12,13 Evidence of substantial charge accumulation in the QD states is provided by results of continuous-wave photoluminescence experiments, in which the ground state interband optical transition is observed to shift by a few 10's of meV to lower (higher) energies for -QDs (+QDs) relative to the ground state in neutral QDs. Room temperature time-resolved photoluminescence experiments were performed with 100 fs, linearlypolarized or circularly-polarized, 1.42 eV pulses from a Ti:sapphire laser tuned to excite carriers near the GaAs band edge.…”

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confidence: 99%

Efficient electron spin detection with positively charged quantum dots

Gündoğdu

Hall

Boggess

et al. 2004

Applied Physics Letters

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We report the application of time-and polarization-resolved photoluminescence up-conversion spectroscopy to the study of spin capture and energy relaxation in positively and negatively charged, as well as neutral, InAs self-assembled quantum dots. When compared to the neutral dots, we find that carrier capture and relaxation to the ground state is much faster in the highly charged dots, suggesting that electron-hole scattering dominates this process. The long spin lifetime, short capture time, and high radiative efficiency of the positively charged dots, indicates that these structures are superior to both quantum well and neutral quantum dot light-emitting diode (LED) spin detectors for spintronics applications.The efficient detection of spin-polarized carriers is a crucial issue for the design of semiconductor-based spintronic devices. 1 A light-emitting diode (LED) configuration employing a quantum well as an optical marker has proven to be an effective means of detecting spin polarized carriers. 2,3 In a spin LED, the degree of circular polarization of the quantum well luminescence provides a direct measure of the spin polarization of the carriers arriving at the spatial location of the quantum well.The application of semiconductor quantum dots (QDs) in such a spin detection scheme is expected to provide a substantial improvement in spin sensitivity over the use of a quantum well. 4,5,6,7 Recent studies of electron spin dynamics in neutral QDs 4,5,8 have revealed that the discrete energy levels in quantum dots arising from three-dimensional quantum confinement blocks the dominant spin relaxation channels present in higher dimensional bulk and quantum well systems, resulting in considerably longer spin relaxation times. Combined with the high optical luminescence efficiency observed in QDs, 9,10,11 these long spin relaxation times should lead to larger spin-dependent luminescence signatures in spin detection applications incorporating QDs as an optical marker. The first spin LED using neutral QDs was recently demonstrated. 6 Few experiments have examined electron spin dynamics in charged quantum dots. 12,13 Through a comparison of spin capture and relaxation dynamics in neutral, positively (+QDs) and negatively (-QDs) charged QDs, we demonstrate that +QDs act as a highly efficient detector for spin-polarized electrons. Our room temperature time-resolved measurements reveal that, following capture of spin-polarized electrons, the initial degree of circular polarization of the QD ground state luminescence is more than four times larger in +QDs compared to neutral QDs. The larger spin signature in +QDs originates from an increased rate of capture of spin polarized electrons through interaction with the built-in hole population, 14,15 as indicated by the early time dynamics of the QD photoluminescence. Rapid electron capture into +QDs reduces spin relaxation in the GaAs barriers prior to capture, resulting in a six-fold enhancement in the time-integrated spin detection efficiency with the incorporation of positiv...

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Zero-field spin quantum beats in charged quantum dots

Cited by 69 publications

References 19 publications

Spin dephasing of doped electrons in charge-tunable InP quantum dots: Hanle-effect measurements

Spin dephasing of doped electrons in charge-tunable InP quantum dots: Hanle-effect measurements

Nuclear-spin effects in singly negatively charged InP quantum dots

Efficient electron spin detection with positively charged quantum dots

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