Measurement of Rashba and Dresselhaus spin-orbit magnetic fields (0709.2509v1)

Abstract: Spin-orbit coupling is a manifestation of special relativity. In the reference frame of a moving electron, electric fields transform into magnetic fields, which interact with the electron spin and lift the degeneracy of spin-up and spin-down states. In solid-state systems, the resulting spin-orbit fields are referred to as Dresselhaus or Rashba fields, depending on whether the electric fields originate from bulk or structure inversion asymmetry, respectively. Yet, it remains a challenge to determine the absolute value of both contributions in a single sample. Here we show that both fields can be measured by optically monitoring the angular dependence of the electrons' spin precession on their direction of movement with respect to the crystal lattice. Furthermore, we demonstrate spin resonance induced by the spin-orbit fields. We apply our method to GaAs/InGaAs quantum-well electrons, but it can be used universally to characterise spin-orbit interactions in semiconductors, facilitating the design of spintronic devices.

• The paper introduces an innovative experimental method to distinguish and measure Rashba and Dresselhaus fields via optical monitoring of electron spin precession.
• It accurately determines SOC constants α and β, revealing that α is comparatively small while β correlates with the quantum well width.
• The study also underscores the role of electric-dipole-induced spin resonance (EDSR) in effectively controlling spin states for advanced spintronic device applications.

Measurement of Rashba and Dresselhaus Spin-Orbit Magnetic Fields

The paper presents significant advancements in the measurement of spin-orbit interactions, specifically Rashba and Dresselhaus fields, in semiconductor quantum wells (QWs). These spin-orbit fields, originating from symmetry-breaking electric fields within materials microstructures, are essential in understanding spin dynamics and designing future spintronic devices. Using an innovative experimental setup, the researchers demonstrate that both Rashba and Dresselhaus fields can be simultaneously and accurately measured through the optical monitoring of electron spin precession in GaAs/InGaAs QWs.

A key contribution of this paper is the detailed methodology for distinguishing between Rashba (derived from structure inversion asymmetry) and Dresselhaus (originating from bulk inversion asymmetry) spin-orbit interactions. By applying an oscillating electric field across a QW, the research team induces changes in the electron drift momentum, which in turn leads to variations in electron spin precession frequencies. This optically monitored precession allows for the calculation of the magnitudes of the Rashba and Dresselhaus fields.

One of the noteworthy outcomes of the experiments is the determination of the SOC constants, $\alpha$ and $\beta$, for the studied samples. Results indicate that $\alpha$ is relatively small due to the lesser valence band offsets in the QWs used, while $\beta$ shows consistent behavior with the sample's width. The precise determination of these constants, without relying solely on beating patterns in phenomena like the Shubnikov-de Haas oscillations, signifies a robust and less ambiguous approach to measuring spin-orbit fields.

The Rashba and Dresselhaus fields were measured for various orientations and conditions, demonstrating consistency across different setups and yielding insights into how these fields can be tuned by external electric fields. This control is paramount for the potential use of these materials in devices like spin transistors, where accurate manipulation of spin phenomena is crucial.

Furthermore, the paper explores electric-dipole-induced spin resonance (EDSR), where an alternating electric field replaces the conventional magnetic field typically used in electron spin resonance (ESR). This method reaffirms the importance of spin-orbit interactions in modern semiconductor research, as they facilitate EDSR by creating an effective magnetic tipping field. These findings underscore the practicality of using spin-orbit fields for efficient control of spin states in potential applications.

From a methodological perspective, the techniques developed here extend beyond just the QWs demonstrated and could be applied to various semiconductor materials. As such, they hold significance for both experimental and theoretical exploration of spintronics. These advancements are not only pivotal for the progression of spin-based technologies but also contribute substantially to the fundamental understanding of spin-orbit coupling dynamics in low-dimensional structures.

Looking forward, this research paves the way for further insights into the interplay between material composition, structural design, and spin-orbit interactions. Future developments may involve exploring the landscape of interchangeability between Rashba and Dresselhaus terms, potentially leading to devices where the detrimental effects of spin decoherence are minimized. As spintronic applications become more prevalent, the methods and findings of this research will undoubtedly be integral to the growth of efficient and practical solutions in information processing and storage technologies.