Dominant role of the shear strain induced admixture in spin-flip processes in self-assembled quantum dots

TL;DR

This paper theoretically investigates spin-flip relaxation in self-assembled InAs/GaAs quantum dots, revealing that shear strain-induced spin admixture is the dominant relaxation mechanism, differing from larger unstrained dots.

Contribution

It identifies shear strain-induced spin admixture as the primary spin-flip relaxation channel in self-assembled quantum dots, emphasizing the importance of strain distribution.

Findings

Shear strain dominates spin-flip relaxation in the studied quantum dots.

The shear strain contribution cannot be simplified to a standard Hamiltonian term.

Constructive interference occurs between two effective spin-phonon terms.

Abstract

We study theoretically the spin-flip relaxation processes for a single electron in a self-assembled InAs/GaAs quantum dot, using an 8-band kp theory in the envelope function approximation. We show that the dominating channel of spin relaxation is spin admixture induced by symmetry-breaking shear strain, which can be mapped onto two effective spin-phonon terms in a conduction band (effective mass) Hamiltonian that have a similar structure and interfere constructively. Unlike the Dresselhaus coupling that dominates spin relaxation in larger, unstrained dots, the shear strain contribution cannot be modeled by a unique standard term in the Hamiltonian but rather relies on the actual strain distribution in the quantum dot.