Strong-Field Resonant Dynamics in Semiconductors

We predict that a direct band gap semiconductor (GaAs) resonantly excited by a strong ultrashort laser pulse exhibits a novel regime: kicked anharmonic Rabi oscillations. In this regime, Rabi oscillations are strongly coupled to intraband motion, and interband transitions mainly take place when electrons pass near the Brillouin zone center where electron populations undergo very rapid changes. The asymmetry of the residual population distribution induces an electric current controlled by the carrier-envelope phase of the driving pulse. The predicted effects are experimentally observable using photoemission and terahertz spectroscopies.

Figure 1

The residual current density $j(F_0,{\phi }_{\mathrm{CE}})$. In these diagrams, the distance to the origin corresponds to the pulse amplitude $F_0$, which varies from zero to $0.8\mathrm{V}/\AA$, while the angle to the horizontal axis encodes the carrier-envelope phase ${\phi }_{\mathrm{CE}}$. The color coding of $F_0^{-3}j(F_0,{\phi }_{\mathrm{CE}})$ is individually normalized for each diagram. Panels (a)–(c) show two-band results (1 VB, 1 CB), while panels (d)–(f) display outcomes of six-band (3 VBs, 3 CBs) calculations. Each horizontal pair of plots corresponds to a certain value of dephasing time $T_2$ as indicated by the labels.

Figure 2

The maximal value of the residual current density $j_{\max }(F_0)={\max }_{{\phi }_{\mathrm{CE}}}[j(F_0,{\phi }_{\mathrm{CE}})]$. The solid and dashed lines were obtained with $T_2=\infty$ and $T_2=10\mathrm{fs}$, respectively. Red curves represent six-band calculations (3 VBs, 3 CBs), whereas blue curves show the two-band results (1 VB, 1 CB).

Figure 3

The residual population of the lowest conduction band $n_{{\mathrm{c}}_1}(k,t_{\max })$ in simulations with two (a)–(c) and six (d)–(f) bands without dephasing ($T_2=\infty$). The CEP of the laser pulse is ${\phi }_{\mathrm{CE}}=0$ in panels (a),(d) and $\pi /2$ in the other plots. Panels (c),(f) display population distributions obtained without intraband motion.

Figure 4

Time dependence of the CB population in the two-band simulation (blue and green curves). It is calculated along reciprocal-space pathways $K(t)$ that satisfy the acceleration theorem. The starting point is the $\mathrm{\Gamma }$ point ($k=0$) for the blue curve and $k=-0.05k_{\max }$ for the green curve. The bold dots on the curves denote moments of passage in the vicinity of the $\mathrm{\Gamma }$ point. The dashed red curve shows the electric field of the pulse ($F_0=0.5\mathrm{V}/\AA$, ${\phi }_{\mathrm{CE}}=\pi /2$).