Intense high-frequency laser-field control of spin-orbit coupling in GaInAs/AlInAs quantum wells: A laser dressing effect

Abstract

The Rashba spin-orbit (SO) coupling can flexibly be controlled via an external gate, while the Dresselhaus term, which mainly depends on quantum confinement, is in general immune to electrical control. Here we theoretically report optical manipulation of the SO coupling by resorting to an intense high-frequency laser field, which ``dresses'' the confining potential for electrons as a result of optical stark effect and enables a flexible and simultaneous control of the Rashba and Dresselhaus couplings. Focusing on ordinary GaInAs/AlInAs quantum wells with two occupied subbands subject to both laser and gate fields, we perform a self-consistent Poisson-Schr\"odinger calculation in the Hartree approximation to determine electro-optical control of the intrasubband (intersubband) Rashba ${\ensuremath{\alpha}}_{\ensuremath{\nu}}$ ($\ensuremath{\eta}$) and Dresselhaus ${\ensuremath{\beta}}_{\ensuremath{\nu}}$ ($\mathrm{\ensuremath{\Gamma}}$) SO terms with $\ensuremath{\nu}=1,2$. Under the impact of laser field, we find that the Rashba terms of the two subbands ${\ensuremath{\alpha}}_{1}$ and ${\ensuremath{\alpha}}_{2}$ may remain locked to equal strength in a broad gate range, providing a means for unified manipulation of the two-subband Rashba couplings. Further, as the laser field varies, we observe that ${\ensuremath{\alpha}}_{1}$ and ${\ensuremath{\alpha}}_{2}$ may have either the same or opposite signs, or even ${\ensuremath{\alpha}}_{2}$ vanishes while ${\ensuremath{\alpha}}_{1}$ is finite, greatly fascinating for selective SO control of distinct subbands. For the Dresselhaus coupling, we disclose two distinct scenarios depending on the interplay of the well width and the laser field strength, and reveal that ${\ensuremath{\beta}}_{2}$ may decrease rapidly when the laser field strengthens, even though ${\ensuremath{\beta}}_{1}$ remains essentially constant. Regarding the intersubband Rashba ($\ensuremath{\eta}$) and Dresselhaus ($\mathrm{\ensuremath{\Gamma}}$) terms, which mainly depend on the overlap and parity of the wave functions of the two subbands, they have relatively weak dependence on the laser field. Moreover, the combined effect of intra- and intersubband SO terms may lead to crossings and avoided crossings of the energy dispersion of multiband spin branches and may even trigger the spin polarization of an originally spin degenerate (unpolarized) band, tunable by the laser field. Our results should stimulate experiments probing the laser field mediated multiband SO control and further enables its spintronic applications.