Optically induced long-lived electron spin coherence in ZnSe∕BeTe type-II quantum wells

Mino, H.; Kouno, Yoshiyasu; Oto, K.; Muro, K.; Akimoto, R.; Takeyama, S.

doi:10.1063/1.2907577

Cited by 19 publications

(17 citation statements)

References 13 publications

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“…The underlying physics is similar to the temperature dependence: the increasing pump density leads to an increase of electron density as well as the thermalization of the electron system, and enhances spin relaxation. Spin relaxation in type-II quantum wells was studied in both GaAs and ZnSe quantum wells at very low temperature [537,538]. As electrons and holes are spatially separated, the electron-hole exchange interaction is weakened and the spin 36 In the metallic regime the spin relaxation rate either decreases with increasing magnetic field or varies as [1/T * 2 (B) − 1/T * 2 (0)] ∼ B 2 due to the g-factor inhomogeneity.…”

Section: Carrier Spin Relaxation At Low Temperature In the Insulatingmentioning

confidence: 99%

Spin dynamics in semiconductors

2010

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This article reviews the current status of spin dynamics in semiconductors which has achieved a lot of progress in the past years due to the fast growing field of semiconductor spintronics. The primary focus is the theoretical and experimental developments of spin relaxation and dephasing in both spin precession in time domain and spin diffusion and transport in spacial domain. A fully microscopic many-body investigation on spin dynamics based on the kinetic spin Bloch equation approach is reviewed comprehensively.Comment: a review article with 193 pages and 1103 references. To be published in Physics Reports

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Section: Carrier Spin Relaxation At Low Temperature In the Insulatingmentioning

confidence: 99%

Spin dynamics in semiconductors

2010

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“…1,[6][7][8][9][10]13,14 However, the energetic barriers in these nanostructures are usually lower than those attainable in colloidal QDs and heteroNCs, which are typically much smaller than their MBE counterparts. Moreover, colloidal chemistry methods are cheaper and easier to upscale than MBE techniques, and offer the additional advantages of processability and easier control over size, shape, and surface.…”

Section: Introductionmentioning

confidence: 99%

“…This offers the possibility of directly controlling the electron-hole wave-function overlap and gives rise to an intermediate carrier localization regime in which one carrier is confined in one of the heteroNC components while the other is delocalized over both materials. 1,2,4 This flexibility in tailoring the optoelectronic properties of the heteronanostructure has important consequences for a number of technologies, and opens up interesting application possibilities: miniaturized low-threshold lasers, 2 photovoltaic devices, 5 fast optical switches, 6 systems for quantum information processing, 7 advanced IR detectors, 8 fast access memories, 9 spintronic devices, 10 and labels for biomedical imaging 11 and optical "nanoscopy" ͑i.e., super-resolution optical microscopy based on stimulated emission depletion 12 ͒. The realization of this wide range of potential applications requires a strict control over the fabrication of the heteronanostructures and a thorough understanding of their properties.…”

Section: Introductionmentioning

confidence: 99%

Formation of nanoscale spatially indirect excitons: Evolution of the type-II optical character of CdTe/CdSe heteronanocrystals

Donegá

2010

Phys. Rev. B

107

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In this work, the evolution of the optical properties of nanoscale spatially indirect excitons as a function of the size, shape, and composition of the heteronanostructure is investigated, using colloidal CdTe/CdSe heteronanocrystals ͑2.6 nm diameter CdTe core and increasing CdSe volume fraction͒ as a model system. Emphasis is given to quantitative aspects such as the absorption cross section of the lowest-energy exciton transition ͑ SS ͒, Stokes shift, linewidths, and the exciton radiative lifetime. The hole wave function remains confined to the CdTe core while the electron wave function is initially delocalized over the whole heteronanocrystal ͑type-I 1/2 regime͒, and gradually localizes in the CdSe segment as the growth proceeds, until the spatially indirect exciton transition becomes the lowest-energy transition ͑type-II regime͒. This results in a progressive shift of the optical transitions to lower energies, accompanied by a decrease in the oscillator strengths at emission energies and an increase in the exciton radiative lifetimes. The onset of the type-II regime is characterized by the loss of structure of the lowest-energy absorption band, accompanied by a simultaneous increase in the Stokes shift values and transition linewidths. This can be understood by considering the dispersion of the hole and electron states in k space. The SS values decrease rapidly in the type-I 1/2 regime but only slightly in the type-II regime. This shows that the indirect exciton formation leads primarily to redistribution of the oscillator strength of the lowest-energy transition over a wider frequency range. The total absorption cross section per ion-pair unit ͑i.e., integrated over all the exciton transitions͒ remains essentially constant during the heteronanocrystal growth, demonstrating that SS is redistributed from higher-energy transitions of both the CdTe and the CdSe segments, in response to the reduction in the electron-hole wavefunction overlap. Two radiative decay rates are observed and ascribed to exciton states with different degrees of localization of the electron wave function ͑an upper state with a faster decay rate and a lower state with a slower decay rate͒. The results presented here provide fundamental insights into nanoscale spatially indirect exciton transitions, highlighting the crucial role of a number of parameters ͑viz., electron-hole spatial correlation, exciton dispersion and exciton degeneracy, shape effects, and electronic coupling͒.

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“…one electron in the ZnSe layer and two holes in the BeTe layer bound each other to comprise the X + complex. The electron Lande g-factor in ZnSe quantum layer is investigated in our previous paper [9], and is determined as . g = 1.11 by the time-resolved Kerr rotation measurement for the 8 nm ZnSe QW, which value is also consistent with those obtained by the magneto-PL measurements in doped samples conducted by the other group [6].…”

Section: Discussionmentioning

confidence: 99%

Spatially indirect photoluminescence of ZnSe/BeTe type II quantum wells in pulsed high magnetic fields

Takeyama

Shen

Enya

et al. 2008

Phys. Status Solidi (c)

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Spatially separated indirect photoemission in a non‐doped ZnSe/BeTe type II quantum structure is investigated by applying pulse magnetic field up to 50 T. The magnetic field dependences of the dichroic photoluminescence (PL) are well explained by an optical transition model associated with a positively charged exciton composed by an electron and two light holes. The PL is suppressed by magnetic field and also by temperature. Weak PL probably arising from localized excitons at interfaces is observed up to the highest magnetic field, and in high temperatures above 20 K. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Optically induced long-lived electron spin coherence in ZnSe∕BeTe type-II quantum wells

Cited by 19 publications

References 13 publications

Spin dynamics in semiconductors

Spin dynamics in semiconductors

Formation of nanoscale spatially indirect excitons: Evolution of the type-II optical character of CdTe/CdSe heteronanocrystals

Spatially indirect photoluminescence of ZnSe/BeTe type II quantum wells in pulsed high magnetic fields

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