Two-dimensional electron gas in the regime of strong light-matter coupling: Dynamical conductivity and all-optical measurements of Rashba and Dresselhaus coupling

A nonperturbative interaction of an electronic system with a laser field can substantially modify its physical properties. In particular, in two-dimensional (2D) materials with a lack of inversion symmetry, the achievement of a regime of strong light-matter coupling allows direct optical tuning of the strength of the Rashba spin-orbit interaction (SOI). Capitalizing on these results, we build a theory of the dynamical conductivity of a 2D electron gas with both Rashba and Dresselhaus SOIs coupled to an off-resonant high-frequency electromagnetic wave. We argue that strong light-matter coupling modifies qualitatively the dispersion of the electrons and can be used as a powerful tool to probe and manipulate the coupling strengths and adjust the frequency range where optical conductivity is essentially nonzero.

Figure 1

The proposed renormalization of the dispersion relation ${\varepsilon }_{\mathbf{p}+}$ is illustrated schematically: The upper surface corresponds to 2DEG with both Rashba and Dresselhaus SOIs with no external field, and the lowest one results from renormalization by field with (4) and (5). To make the effect of renormalization more pronounced in (6) we put $2m=1,\beta /\alpha =12/15$, and $\gamma =0.2$.

Figure 2

Components of the conductivity tensor (11) $\mathrm{Re}{\sigma }_{xx}\left(\omega \right)$ and $\mathrm{Re}{\sigma }_{xy}\left(\omega \right)$ plotted for different values of the field-matter coupling $\gamma =e{E}_0\sqrt{{\alpha }^2+{\beta }^2}/\left(\hslash {\mathrm{\Omega }}^2\right)$ with a fixed ratio $\beta /\alpha =0.125$. The red solid line specifies the case with no dressing. An increase in the field-matter coupling results in the frequency domain being broadened and shifting slightly past the original position. The dashed area in the inset to the top panel shows the integration area in (11), while the two peaks on the main plots correspond precisely to the frequencies $\omega ={\omega }_a$ and $\omega ={\omega }_b$.

Figure 3

Components of the conductivity tensor (11) $\mathrm{Re}{\sigma }_{xx}\left(\omega \right)$ and $\mathrm{Re}{\sigma }_{xy}\left(\omega \right)$ plotted for the fixed field-matter coupling $\gamma =0.3$ and the relative strength of spin-orbit coupling $\beta /\alpha =0.125$, 0.33, and 0.5. The two-peak structure outlined in the main text is clearly visible, allowing for independent experimental determinations of the Rashba and Dresselhaus couplings. The conductivity of a pure Rashba system is plotted in the top panel (solid line). One can observe that a pure Rashba (or Dresselhaus) structure is characterized by a constant value in a more narrow interval of frequency domain.