Subsecond Spin Relaxation Times in Quantum Dots at Zero Applied Magnetic Field Due to a Strong Electron-Nuclear Interaction

Abstract

A key to ultralong electron spin memory in quantum dots (QDs) at zero magnetic field is the polarization of the nuclei, such that the electron spin is stabilized along the average nuclear magnetic field. We demonstrate that spin-polarized electrons in n-doped (In,Ga)As/GaAs QDs align the nuclear field via the hyperfine interaction. A feedback onto the electrons occurs, leading to stabilization of their polarization due to formation of a nuclear spin polaron [I. A. Merkulov, Phys. Solid State 40, 930 (1998)]. Spin depolarization of both systems is consequently greatly reduced, and spin memory of the coupled electron-nuclear spin system is retained over 0.3 sec at temperature of 2 K.

Stabilization of the Electron-Nuclear Spin Orientation in Quantum Dots by the Nuclear Quadrupole Interaction

“…Polarized nuclei create an effective magnetic field due to the hyperfine interaction that suppresses the electron spin relaxation similarly to the external field. The dynamic nuclear polarization in a low external field (1-10 G) was observed in charged InP/InGaP [5], InGaAs/GaAs [6], InAs/GaAs [7] and CdSe/ZnSe [8] QDs.…”

“…In a weak magnetic field ( should be carefully analyzed in any (self-organized) quantum dot system having nuclei with large spin I>1/2. For example, the QI may explain qualitatively the zero-field nuclear polarization in InP [5] and InAs [7] dots as well as the surprising long-term conservation of spin polarization in the electron-nuclear spin system of InGaAs QD [6]. (1) is applicable when the resident electron dwell time (correlation time) within the QD is short: electron spin has no time to make a turn about a random nuclear field.…”

Nuclear spin effects in semiconductor quantum dots

“…Similarly to PL, in resonant optical measurements on single dots, such as differential transmission 38 or resonance fluorescence 39 , the Overhauser shifts can be measured with high accuracy. In measurements on ensembles of QDs, the average degree of nuclear polarization can be extracted either from detailed analysis of PL polarization 40 or from ultra-fast optical measurements of the Larmor precession of electrons 41 .…”

Exciton Fine-Structure Splitting in Self-Assembled Lateral InAs/GaAs Quantum-Dot Molecular Structures

“…[9][10][11] This is largely motivated by the expectations that QDs are efficient light emitters and possess long electron spin relaxation/coherence time. 12,13 The photons emitted from the QDs are a result of excitonic recombination, which is associated with electron-heavy hole (e-hh) exchange-coupled pairs in most of the known semiconductor QD systems. It has now been well established that an anisotropic exchange interaction (AEI) can split the doublet of the bright neutral exciton states into two spinmixed, linearly polarized |H and |V exciton states, commonly referred to as a fine-structuresplitting (FSS).…”