Dynamic nuclear polarization in InGaAs/GaAs and GaAs/AlGaAs quantum dots under nonresonant ultralow-power optical excitation

Abstract

Article:Puebla, J., Chekhovich, E.A., Hopkinson, M. orcid.org/0000-0002-8097-6913 et al. (4 more authors) (2013) Dynamic nuclear polarization in InGaAs/GaAs and GaAs/AlGaAs quantum dots under nonresonant ultralow-power optical excitation. Physical Review B, 88 (4 ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. We study experimentally the dependence of dynamic nuclear spin polarization on the power of non-resonant optical excitation in two types of individual neutral semiconductor quantum dots: InGaAs/GaAs and GaAs/AlGaAs. We show that the mechanism of nuclear spin pumping via second order recombination of optically forbidden ("dark") exciton states recently reported in InP/GaInP quantum dots [Phys. Rev. B 83, 125318 (2011)] is relevant for material systems considered in this work. In the InGaAs/GaAs dots this nuclear spin polarization mechanism is particularly pronounced, resulting in Overhauser shifts up to ∼80 µeV achieved at optical excitation power ∼1000 times smaller than the power required to saturate ground state excitons. The Overhauser shifts observed at low-power optical pumping in the interface GaAs/AlGaAs dots are generally found to be smaller (up to ∼40 µeV). Furthermore in GaAs/AlGaAs we observe dot-to-dot variation and even sign reversal of the Overhauser shift which is attributed to dark-bright exciton mixing originating from electron-hole exchange interaction in dots with reduced symmetry. Nuclear spin polarization degrees reported in this work under ultra-low power optical pumping are comparable to those achieved by techniques such as resonant optical pumping or above-gap pumping with high power circularly polarized light. Dynamic nuclear polarization via second-order recombination of "dark" excitons may become a useful tool in single quantum dot applications, where manipulation of the nuclear spin environment or electron spin is required.

Pulse control protocols for preserving coherence in dipolar-coupled nuclear spin baths

“…38 : the QD sample is kept at low temperature ( T = 4.2 K) and is subjected to a strong magnetic field B z = 8 T. Using a confocal microscopy setup in Faraday configuration, we prepare the nuclear spin bath optically through polarisation-selective pumping of an exciton transition (dynamic nuclear polarisation). In this way, we achieve hyperfine-mediated spin bath polarisation degrees of up to 65% 39,40 . Radio frequency (rf) fields are coupled to the QD via a multi-winding copper coil in close proximity to the sample.…”

Suppression of nuclear spin bath fluctuations in self-assembled quantum dots induced by inhomogeneous strain

“…The cycle starts with optical nuclear spin pumping 22 32 using high-power σ + circularly polarized laser [stage (a)]. Spin polarized electrons of highly excited and/or multiexcitonic states transfer their polarization to nuclear spins via the hyperfine interaction 35 . The pump duration is chosen long enough (~3–7 s depending on magnetic field B z ) to achieve the steady-state nuclear spin polarization.…”

Dark-bright exciton coupling in asymmetric quantum dots

“…The brightening of the DE, opening the way to an alloptical manipulation scheme, is theoretically predicted to occur by symmetry breaking of the QD potential [6,8]. Atomistic calculations reported in Ref.…”