Spin-helix Larmor mode

Shahrzad Karimi,Irene D’Amico,Carsten A Ullrich,Florent Perez

doi:10.1038/s41598-018-21818-8

Shahrzad Karimi, Irene D’Amico + Show 2 more

Open Access

https://doi.org/10.1038/s41598-018-21818-8

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Journal: Scientific Reports	Publication Date: Feb 22, 2018
Citations: 1	License type: open-access

Affiliation: University of Missouri, University of York

Abstract

A two-dimensional electron gas (2DEG) with equal-strength Rashba and Dresselhaus spin-orbit coupling sustains persistent helical spin-wave states, which have remarkably long lifetimes. In the presence of an in-plane magnetic field, there exist single-particle excitations that have the character of propagating helical spin waves. For magnon-like collective excitations, the spin-helix texture reemerges as a robust feature, giving rise to a decoupling of spin-orbit and electronic many-body effects. We prove that the resulting spin-flip wave dispersion is the same as in a magnetized 2DEG without spin-orbit coupling, apart from a shift by the spin-helix wave vector. The precessional mode about the persistent spin-helix state is shown to have an energy given by the bare Zeeman splitting, in analogy with Larmor’s theorem. We also discuss ways to observe the spin-helix Larmor mode experimentally.

Highlights

A two-dimensional electron gas (2DEG) with equal-strength Rashba and Dresselhaus spin-orbit coupling sustains persistent helical spin-wave states, which have remarkably long lifetimes
The Rashba and Dresselhaus spin-orbit coupling (SOC) fields will be introduced in ′, but it will be convenient for the discussion of spin waves to work in a coordinate system which is oriented such that its x and z axes lie in the quantum well plane, and the z-axis points along the in-plane magnetic field B
We have considered the spin dynamics in a 2DEG in the presence of SOC, under the very special condition where the Rashba and Dresselhaus coupling strengths are equal (α = β) and where an in-plane magnetic field is applied perpendicular to the [110] direction

Summary

Introduction

A two-dimensional electron gas (2DEG) with equal-strength Rashba and Dresselhaus spin-orbit coupling sustains persistent helical spin-wave states, which have remarkably long lifetimes. We will study spin waves in a 2DEG in the presence of in-plane magnetization and SOC This system exhibits a rich interplay between Coulomb many-body effects, Rashba and Dresselhaus SOC, applied magnetic field, and electron density, which we have studied earlier[9,16,17,18]. We here consider a 2DEG embedded in a zincblende quantum well grown along the [001] direction: SU(2) symmetry is partially restored, and a helical spin texture can be sustained along the [110] direction This result is robust against spin-independent disorder scattering and Coulomb interactions[20]. The main experimental signature of this state is that spin packet excitations are protected from decoherence, leading to extraordinarily long lifetimes[22,25]

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