  We theoretically investigate the real-time transient responses of a
two-dimensional (2D) electron gas with anisotropic Rashba spin-orbit coupling
(SOC) to laser pulses. Through explicitly monitoring the time-dependent
photocurrents and spin polarization under different linear polarizations of the
laser pulse, we find that the transient breaking of the mirror symmetry in
combination with the anisotropy of the Rashba SOC results in significant
distinction between the charge-mediated and the spin-mediated contributions to
the photocurrents. Such distinction is obtained by analyzing the dependence of
the symmetry-breaking induced (transverse) components of the photocurrents on
the linear polarization angle of the laser pulse. This suggests a possibility
of inferring spin-mediated processes in photocurrents without the use of
circularly polarized lights. Moreover, the interplay between transient symmetry
breaking and the anisotropy of the Rashba SOC also leads to transiently nonzero
spin polarization components that are otherwise zero in the steady-state limit
and the linear response regime. Especially, the out-of-plane spin polarization
component can be induced or turned off by controlling the relative orientation
of the linear polarization with respect to the symmetry axis of the 2D
electronic system, without involving material-intrinsic magnetization effects.
Our findings demonstrate the efficacy of a particular coordination between the
polarization of the ultrafast laser pulses and the spatial symmetry of the
electronic materials in directing the real-time charge and the spin responses
that are fundamental to the development of ultrafast spintronics in solid
states.
