We study the photoinduced manipulation of charge carriers in monolayer silicene subject to intense electromagnetic terahertz radiation. Considering the Dirac cone approximation and going beyond the off-resonant condition for large frequencies of the radiation field, where only virtual photon processes are allowed, we present the exact zero-momentum pseudospin polarization and numerical results for the quasienergy band structure and time-averaged density of states. We find that resonant processes, due to real photon emission and absorbtion processes, induce a band inversion that qualitatively modifies the quasienergy spectrum. These band-structure changes manifest themselves as an inversion of the averaged pseudospin polarization. Through the analysis of the time-averaged density of states we find that effective photoinduced gap manipulation can only be achieved in the intermediate and strong matter-radiation coupling regime where the off-resonant approximation breaks down.

International audienceWe present perturbative analytical results of the Landau level quasienergy spectrum, autocorrelation function, and out-of-plane pseudospin polarization for a single graphene sheet subject to intense circularly polarized Terahertz radiation. For the quasienergy spectrum, we find a striking nontrivial level-dependent dynamically induced gap structure. This photoinduced modulation of the energy band structure gives rise to shifts of the revival times in the autocorrelation function and it also leads to modulation of the oscillations in the dynamical evolution of the out-of-plane pseudospin polarization, which measures the angular momentum transfer between light and graphene electrons. For a coherent state, chosen as an initial pseudospin configuration, the dynamics induces additional quantum revivals of the wave function that manifest as shifts of the maxima and minima of the autocorrelation function, with additional partial revivals and beating patterns. These additional maxima and beating patterns stem from the effective dynamical coupling of the static eigenstates. We discuss the possible experimental detection schemes of our theoretical results and their relevance in new practical implementation of radiation fields in graphene physics

Raman Spectroscopy and magneto-photoluminescence measurements under high magnetic fields were used to investigate optical and spin properties of GaBiAs/GaAs multiple quantum wells (MQWs). An anomalous negative diamagnetic shift was observed at higher temperatures and higher laser intensities and was associated to a sign inversion of hole effective mass in these structures. In addition, it was observed an enhancement of polarization degree with decreasing of laser intensity (experimental condition where the emission is dominated by localized excitons). This effect was explained by an increase of spin relaxation times due to exciton localization by disorder. 2 I.INTRODUCTIONIII-V dilute bismide semiconductor material has attracted much attention in recent years due to its potential applications for near infrared wavelength photonics and spintronics [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. The incorporation of Bi has been shown to have a dramatic impact on the band structure of GaAs. A band gap reduction of around 90 meV per percent of Bi and a large increase of spin-orbit (SO) split-off energy have been observed [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. This increase of spin-orbit interaction could suppress the non-radiative Auger recombination processes that affect the efficiency of lasers in the near infrared; it is also very attractive for semiconductor spintronics. On the other hand, GaBiAs alloys have important disorder effects mainly due to potential fluctuations associated to Bi composition variation and the formation of clusters [18][19][20]. These disorder effects have significant impacts on the optical emission of this material. Therefore, the investigation of disorder effects is an important issue for bismide alloys in photonics and spintronics; particularly for GaBiAs/GaAs quantum wells (QWs), which are important for further development of GaBiAs based devices.Recently, much attention has been paid to the spin properties of GaBiAs alloys.A decrease of spin relaxation times was observed for GaBiAs alloys and associated to the increase of spin-orbit (SO) split-off energy. It was also reported that the g-factor of GaBiAs is highly anisotropic and that its value increases strongly with the increasing Bi composition [18]. These spin properties were theoretically explained by an important increase of spin-orbit-splitting energy and hybridization of the extended states of the 3 GaAs valence band edge with localized Bi-related states in disordered GaBi x As 1−x alloys [18].In this paper, we have investigated the effect of disorder on the optical and spin properties of GaBiAs/GaAs multiple quantum wells (MQWs). We have observed an anomalous negative diamagnetic shift at higher temperatures and higher laser intensities (experimental conditions under which the emission is dominated by free excitons). This result evidences negative values of hole effective mass in these materials. An enhancement of polarization degree at lower energies (experimental co...

In this chapter, we describe some of our recent results on the laser-induced manipulation of the energy band structure of graphene-like systems. We present numerical results on the quasi-energy spectrum as well as detailed calculations of semi-analytical approximations to other physical quantities of interest. The main message we would like to convey to the interested reader of the chapter is that by properly tuning the perturbation parameters of the radiation field one can control the size and shape of the photoinduced gaps. These in turn would allow the realization of new electronic phases on graphene and its related materials such as silicene.

A spin filtering device using quantum spin interference is theoretically proposed in a GaAs/AlGaAs electron gas that has both Rashba and Dresselhaus spin-orbit couplings. The device achieves polarized electron currents by separating spin up and spin down components without a magnetic field gradient. We find two broad spin filtering regimes, one where the interferometer has symmetrical arms, where a small magnetic flux is needed to achieve spin separation, and the other with asymmetric arms where the change in path length renders an extra phase emulating the effects of a magnetic field. We identify operating points for the device where optimal electron polarization is achieved within value ranges found in a 2D electron gas. Both device setups apply for arbitrary incoming electron polarization and operate at broad energy ranges within the incoming electron band. 03.65.Vf