Spin-relaxation time in materials with broken inversion symmetry and large spin-orbit coupling

Lénárd Szolnoki,Ferenc Simon,Annamária Kiss,Balázs Dóra

doi:10.1038/s41598-017-09759-0

Abstract

We study the spin-relaxation time in materials where a large spin-orbit coupling (SOC) is present which breaks the spatial inversion symmetry. Such a spin-orbit coupling is realized in zincblende structures and heterostructures with a transversal electric field and the spin relaxation is usually described by the so-called D’yakonov-Perel’ (DP) mechanism. We combine a Monte Carlo method and diagrammatic calculation based approaches in our study; the former tracks the time evolution of electron spins in a quasiparticle dynamics simulation in the presence of the built-in spin-orbit magnetic fields and the latter builds on the spin-diffusion propagator by Burkov and Balents. Remarkably, we find a parameter free quantitative agreement between the two approaches and it also returns the conventional result of the DP mechanism in the appropriate limit. We discuss the full phase space of spin relaxation as a function of SOC strength, its distribution, and the magnitude of the momentum relaxation rate. This allows us to identify two novel spin-relaxation regimes; where spin relaxation is strongly non-exponential and the spin relaxation equals the momentum relaxation. A compelling analogy between the spin-relaxation theory and the NMR motional narrowing is highlighted.

Highlights

It is an intriguing possibility to employ the electron spins as information carriers
We note that we focus on the effect of inversion symmetry breaking spin-orbit coupling (SOC) fields on spin-relaxation and we do not discuss other mechanisms, such as e.g. the Elliott-Yafet mechanism[3, 4]
The time evolution of the electron spin direction in the presence of internal spin-orbit coupling is studied with a Monte Carlo approach which essentially mimics the mathematical description of D’yakonov and Perel’[5, 6]: an initially polarized electron spin ensemble travels in a solid where the SOC

Summary

Introduction

It is an intriguing possibility to employ the electron spins as information carriers (known as spintronics[1]) This prospect has revived the experimental and theoretical studies of spin-relaxation in semiconductors and metals. 7. The DP theory describes the dominant spin-relaxation mechanism in large band-gap III–V semiconductors (e.g. GaAs) with the zincblende structure (the so-called bulk inversion asymmetry) and for semiconductor heterostructures with an applied transversal electric field (the so-called structure inversion asymmetry). The DP theory describes the dominant spin-relaxation mechanism in large band-gap III–V semiconductors (e.g. GaAs) with the zincblende structure (the so-called bulk inversion asymmetry) and for semiconductor heterostructures with an applied transversal electric field (the so-called structure inversion asymmetry) These two cases are known as Dresselhaus or Bychkov-Rashba spin-orbit coupling (SOC), respectively.

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Conclusion