Search

We propose an ultrafast all-optical anomalous Hall effect in two-dimensional (2D) semiconductors of hexagonal symmetry such as gapped graphene (GG), transition metal dichalcogenides (TMDCs), and hexagonal boron nitride (h-BN). To induce such an effect, the material is subjected to a sequence of two strong-field single-optical-cycle pulses: A chiral pump pulse followed within a few femtoseconds by a probe pulse linearly polarized in the armchair direction of the 2D lattice. Due to the effect of topological resonance, the first (pump) pulse induces a large chirality (valley polarization) in the system, while the second pulse generates a femtosecond pulse of the anomalous Hall current. The proposed effect is fundamentally the fastest all-optical anomalous Hall effect possible in nature. It can be applied to ultrafast all-optical storage and processing of information, both classical and quantum.

We study the interaction of graphene quantum dots (GQDs) with ultrashort and strong optical pulses theoretically. An important characteristic of such interaction is the energy accumulated by GQDs after the pulse. We show that the GQD absorbance has a highly nonlinear dependence on the field amplitude. At small-field amplitudes, the absorbance strongly depends on the frequency of the pulse and the band gap of a QD, i.e., its size. At large-field amplitudes, $\ensuremath{\sim}1$ V/\AA{}, the absorbance has a weak nonmonotonic dependence on the size of the dot with its maximum value of $\ensuremath{\approx}4.5$% realized for GQD consisting of $\ensuremath{\approx}60$ atoms. As a function of the field amplitude, the absorbance also has a maximum, the position of which depends on the size of the dot.

In topological materials, interacting with short and strong optical pulses, electrons can accumulate a topological phase during the pulse. Such phase can compensate the dynamic phase resulting in topological resonance, which is visible as a large inter-band transfer of electron population. We study theoretically the topological resonance in materials of the gapped multilayer graphene type. We show that the resonance can be observed only in the systems with finite bandgap. For graphene monolayer the topological resonance can occur only in the field of an elliptically polarized pulse, while for graphene systems with many layers the topological resonance can be also realized in a linearly polarized pulse.

We theoretically study the interaction of an ultrafast intense linearly polarized optical pulse with monolayers of transition metal dichalcogenides (TMDCs). Such a strong pulse redistributes electrons between the bands and generates femtosecond currents during the pulse. Due to the large bandwidth of the incident pulse, this process is completely an off-resonant. While in TMDCs, the time-reversal symmetry is conserved, the inversion symmetry is broken, and these monolayers have axial symmetry along the armchair direction but not along with the zigzag one. The pulse, polarized along with asymmetric directions of TMDC monolayer, generates both longitudinal, i.e., along the direction of polarization, and transverse, i.e., in the perpendicular direction, currents. Such currents result in charge transfer through the system. We study different TMDC materials and show how the femtosecond transport in TMDC monolayers depend on their parameters, such as lattice constant and bandgap.

In two-dimensional hexagonal semiconductors, we show that an applied ultrafast strong optical pulse results in a finite conduction band population and generates both longitu- dinal and transverse electric currents during and after the pulse.

We theoretically study a topological nanospaser, which consists of a silver nanospheroid and MoS$_2$ monolayer ake of a circular shape. The metal nanospheroid acts as a plasmonic nanoresonator that supports two rotating modes, which are coupled to the corresponding valleys of MoS$_2$. We apply external circularly polarized light that selectively pumps only one of the valleys of MoS$_2$. The generated spaser dynamics strongly depends on the size (radius) of the MoS$_2$ nanoflake. For small radius, the system has only one spasing regime when only chirally-matched plasmon mode is generated, while at larger size of MoS$_2$, depending on the pump intensity, there are two regimes. In one regime, only the chirally-matched plasmon mode is generated, while in the other regime both chirally-matched and chirally-mismatched modes exist. Different regimes of spaser operation have also opposite handedness of the far-field radiated of the spaser system. Such topological nanospaser has potential applications in different areas of infrared spectroscopy, sensing, probing, and biomedical treatment., Comment: 12 pages, 8 figures

We theoretically investigate the interaction of an ultrastrong femtosecond-long linearly polarized optical pulse with AB-stacked bilayer graphene (BLG). The pulse excite electrons from the valence into the conduction band (CB), resulting in finite CB population. Such a redistribution of electrons results in the generation of current which can be manipulated by the angle of incidence of the pulse. For the normal incidence, the current along a direction transverse to the polarization of the optical pulse is zero. However, the interlayer symmetry is broken up by a finite angle of incidence due to which BLG possesses a single axis of symmetry. Thus, for an oblique incidence, if the pulse is polarized normal to the symmetry axis then there is an induction of electric current in the direction perpendicular to the polarization of the pulse. We show that the magnitude and the direction of such a current as well as charge transfer along this direction can be manipulated by tuning the angle of incidence of the laser pulse. Further, the symmetry of the system prohibits the generation of transverse current if the pulse is polarized along the axis of symmetry of BLG.

We study theoretically the strong-field absorption of an ultrafast optical pulse by a gapped graphene monolayer. At low field amplitudes, the absorbance in the pristine graphene is equal to the universal value of $2.3$ percent. Although the ultrafast optical absorption for low field amplitudes is independent of the polarization, linear or circular, of the applied optical pulse, for high field amplitudes, the absorption strongly depends on the pulse polarization. For a linearly polarized pulse, the optical absorbance is saturated at the value of $\approx 1.4$ percent for the pulse's amplitude of $\geq 0.4~\mathrm{V/\AA}$, but no such saturation is observed for a circularly polarized pulse. For the gapped graphene, the absorption of a linearly polarized pulse has a weak dependence on the bandgap, while for a circularly polarized pulse, the absorption is very sensitive to the bandgap. %Opening a bandgap in graphene by placing in on, for example, SiC substrate strongly modify the ultrafast absorption at small field amplitudes.

We study theoretically interaction of a bilayer graphene with a circularly polarized ultrafast optical pulse of a single oscillation at an oblique incidence. The normal component of the pulse breaks the inversion symmetry of the system and opens up a dynamical band-gap, due to which a valley-selective population of the conduction band becomes sensitive to the angle of incident of the pulse. We show that the magnitude of the valley polarization can be controlled by the angle of incidence, the amplitude, and the angle of in-plane polarization of the chiral optical pulse. Subsequently, a sequence of a circularly polarized pulse followed by a linearly polarized femtosecond-long pulse can be used to control the valley polarization created by the preceding pulse. Generally, the linearly polarized pulse depolarizes the system. The magnitude of such a depolarization depends on the amplitude, and the in-plane polarization angle of the linearly polarized pulse. Our protocol provides a favorable platform for applications in valleytronics., arXiv admin note: text overlap with arXiv:2004.09732

We theoretically introduce a topological spaser, which consists of a hexagonal array of plasmonic metal nanoshells containing an achiral gain medium in their cores. Such a spaser can generate two mutually time-reversed chiral surface plasmon modes in the $\mathbf K$- and $\mathbf K^\prime$-valleys, which carry the opposite topological charges, $\pm1$, and are described by a two-dimensional $E^{\prime}$ representation of the $D_{3h}$ point symmetry group. Due to the mode competition, this spaser exhibits a bistability: only one of these two modes generates, which is a spontaneous symmetry breaking. Such a spaser can be used for an ultrafast all-optical memory and information processing, 9 pages, 7 figures

We theoretically study the Dirac fermion dynamics in a graphene monolayer in the presence of an applied ultrafast laser pulse. The pulse has the duration of a few femtoseconds and the amplitude of ~ 0.1 - 0.5 $\mathrm{V/\AA}$. The waveform of the pulse is described by Hermit Gaussian polynomials with varying carrier-envelope phase. We show that the ultrafast dynamics of Dirac fermions strongly depends on the carrier-envelope phase and the frequency of the applied pulse. The ultrafast pulse generates an electric current which results in a finite transferred charge. The ultrafast field-driven current and the corresponding net transferred charge depend on the waveform of the applied pulse. Our results pave the way for the development of ultrafast information processing in the terahertz domain.

We theoretically study the interaction of ultrashort optical pulses with gapped graphene. Such a strong pulse results in a finite conduction band population and a corresponding electric current, both during and after the pulse. Since gapped graphene has broken inversion symmetry, it has an axial symmetry about the y -axis but not about the x-axis. We show that, in this case, if the linear pulse is polarized along the x-axis, the rectified electric current is generated in the y direction. At the same time, the conduction band population distribution in the reciprocal space is symmetric about the x-axis. Thus, the rectified current in gapped graphene has an inter-band origin, while the intra-band contribution to the rectified current is zero.

We study theoretically the ultrafast electron dynamics of three-dimensional Weyl semimetals in the field of a laser pulse. For a circularly-polarized pulse, such dynamics is governed by topological resonance, which manifests itself as a specific conduction band population distribution in the vicinity of the Weyl points. The topological resonance is determined by the competition between the topological phase and the dynamic phase and depends on the handedness of a circularly polarized pulse. Also, we show that the conduction band population induced by a circularly-polarized pulse that consists of two oscillations with opposite handedness is highly chiral, which represents the intrinsic chirality of the Weyl points.

For gapped graphene, we predict that an intense ultrashort (single-oscillation) circularly polarized optical pulse can induce a large population of the conduction band and a large valley polarization. With an increase in the band gap, the magnitude of the valley polarization gradually increases from zero (for the native gapless graphene) to a value on the order of unity. The energy bandwidth of the electrons excited into the conduction band can be very large ($\ensuremath{\gtrsim}10$ eV for a reasonable pulse amplitude of $\ensuremath{\sim}0.5$ V/\AA{}). These phenomena are due to the effect of topological resonance: The matching of the topological (geometric) phase and the dynamic phase. Gapped graphene with a tunable band gap can be used as a convenient generic model of two-dimensional semiconductors with honeycomb generic lattice structures and broken inversion symmetry, such as transition-metal dichalcogenides.

In this paper, we broadly investigate the interaction of Dirac materials (silicene and germanene) with a few-femtosecond intense optical pulse. We show that electron dynamics in such a short optical pulse is coherent, and its reversibility can be controlled by the polarization of the optical pulse, as well as the direction of propagation, i.e., angle of incidence. By varying the incident angle of the pulse, one can change the electron dynamics from highly irreversible at small angle of incidence (with respect to normal of the plane) to almost fully reversible at large angles. The reversibility of electron dynamics is also sensitive to the polarization of the pulse relative to the orientation of crystallographic planes in silicene/germanene. Such control of electron dynamics in buckled graphene materials is due to the sensitivity of interband coupling in buckled materials with respect to the component of optical field perpendicular to the silicene/germanene monolayer.

We investigate the effects of varying temperature and chemical potential on the optical absorption spectrum of (001) surface states of topological crystalline insulator SnTe using a four-band effective k ⋅ p Hamiltonian. The spectrum is characterized by a narrow peak at 52 meV and a shoulder feature at 160 meV. Both absorptions have maximal intensity at 0 K or when chemical potential is located at the charge neutrality point. Then, as temperature increases or as chemical potential diverges, they both decrease in intensity. The 52 meV peak originates from transitions between high density of states regions surrounding van Hove singularities and is the spectrum’s most prominent feature. Additionally, a third absorption from 110 meV to 150 meV, initially absent at 0 K or chemical potential at charge neutrality point, gradually builds in intensity as temperature increases or as chemical potential diverges. This absorption arises from transitions between low and high energy bands of opposite helicity. Importantly, we find that all distinct spectral features are diminished if the magnitude of chemical potential diverges to values above the van Hove singularity energies. If a given sample’s chemical potential is well-controlled, conventional infrared spectroscopy may be used to identify the spectral signatures of SnTe (001) surface states at room temperatures and without use of large magnetic fields.

We study numerically interaction of phosphorene monolayer with a strong femtosecond-long optical pulse. For such a short pulse, the electron dynamics is coherent and can be described by the time-dependent Schr\"odinger equation. Strong optical field of the pulse causes redistribution of electrons between the conduction and valence bands. Such interband dynamics is highly irreversible, i.e., the conduction band population after the pulse is large and comparable to the maximum conduction band during the pulse. The conduction band population distribution in the reciprocal space shows high contrast hot spots, which are due to large interband coupling at the $\mathrm{\ensuremath{\Gamma}}$ point. The optical pulse also causes the net charge transfer through the phosphorene monolayer. The direction of the transfer is the same as the direction of the field maximum.

We predict that a single oscillation of a strong optical pulse can significantly populate the surface conduction band of a three-dimensional topological insulator, Bi2Se3. Both linearly- and circularly-polarized pulses generate chiral textures of interference fringes of population in the surface Brillouin zone. These fringes constitute a self-referenced electron hologram carrying information on the topology of the surface Bloch bands, in particular, on the effect of the warping term of the low-energy Hamiltonian. These electron-interference phenomena are in a sharp contrast to graphene where there are no chiral textures for a linearly-polarized pulse and no interference fringes for circularly-polarized pulse. These predicted reciprocal space electron-population textures can be measured experimentally by time resolved angle resolved photoelectron spectroscopy (TR-ARPES) to gain direct access to non-Abelian Berry curvature at topological insulator surfaces., Comment: 10 pages, 10 figures

Bloch electrons in a perpendicular magnetic field exhibit unusual dynamics that has been studied for more than half a century. The single-electron energy spectrum of this system, the Hofstadter butterfly has been the subject of theoretical and experimental investigations for the past two decades. Experimental observation of these unusual spectra in semiconductor nanostructures, however, met with only limited success. The fractal nature of the butterfly spectrum was finally observed in 2013, thanks to the unique electronic properties of graphene. Here, the authors present an overview of the theoretical understanding of Hofstadter butterflies in monolayer and bilayer graphene. First, they briefly discuss the energy spectra in conventional semiconductor systems. The electronic properties of monolayer and bilayer graphene are then presented. Theoretical background on the Moire pattern in graphene and its application in the magnetoconductance probe that resulted in graphene butterflies are explained. They have also touched upon the important role of electron–electron interaction in the butterfly pattern in graphene. Experimental efforts to investigate this aspect of fractal butterflies have just begun. They conclude by discussing the future prospects of butterfly search, especially for interacting Dirac fermions in graphene.

We discuss the topological properties of graphene superlattices excited by ultrafast circularly-polarized laser pulses with strong electric field amplitude, aiming to directly observe of the Berry phase, a geometric quantum phase encoded in the graphene’s electronic wave function. As a continuing research on our recent paper, Phys. Rev. B 96, 075409, we aim to show that the broken symmetry system of graphene superlattice and the Bragg reflection of electrons creates diffraction and “which way” interference in the reciprocal space reducing the geometrical phase shift and making it directly observable in the electron interferograms. Such a topological phase shift acquired by a carrier moving along a closed path of crystallographic wave vector is predictably observable via time and angle resolved photoemission spectroscopy (tr-ARPES). We believe that our result is an essential step in control and observation of ultrafast electron dynamics in topological solids and may open up a route to all-optical switching, ultrafast memories, and petahertz-scale information processing technologies.

We propose and theoretically explore states of graphene superlattices with relaxed $\mathcal{P}$ and $\mathcal{T}$ symmetries created by strong circularly polarized ultrashort pulses. The conduction-band electron distribution in the reciprocal space forms an interferogram with discontinuities related to topological (Berry) fluxes at the Dirac points. This can be studied using time- and angle-resolved photoemission spectroscopy (TR-ARPES). Our findings hold promise for control and observation of ultrafast electron dynamics in topological solids and may be applied to petahertz-scale information processing.

We theoretically study the interaction of crystalline topological insulator (CTIs), characterized by surface quadratic gapless bands, with an ultrashort (few-femtosecond) optical pulse. The electron dynamics in such an optical pulse is determined by a strong lattice-momentum dependence of the interband dipole coupling, which is anisotropic and singular at the degeneracy point. The interband mixing induced by the ultrashort pulse results in a finite conduction band population, the distribution of which in the reciprocal space is correlated with the profile of the interband dipole matrix elements and has high contrast. The number of such high-contrast regions depends on the polarization direction of the optical pulse. The ultrashort pulse also causes an electrical current and a net charge transfer through the system in the direction of the maximum field. These findings open up roots to ultrafast optical-field control of the CTIs and petahertz-band optoelectronics.

We theoretically introduce the fundamentally fastest induction of a significant population and valley polarization in a monolayer of a transition metal dichalcogenide (i.e., $\mathrm{MoS_2}$ and $\mathrm{WS_2}$). This may be extended to other two-dimensional materials with the same symmetry. This valley polarization can be written and read-out by a pulse consisting of just a single optical oscillation with a duration of a few femtoseconds and an amplitude of $\sim0.2~\mathrm V/\mathrm{\AA}$. Under these conditions, we predict a new effect of {\em topological resonance}, which is due to Bloch motion of electrons in the reciprocal space where electron population textures are formed defined by non-Abelian Berry curvature. The predicted phenomena can be applied for information storage and processing in PHz-band optoelectronics., Comment: 9 pages, 7 figures

We report on the direct manifestation of topological nature of graphene in the conduction band population distribution without a magnetic field. The crystalline structure of graphene coupled to a nanowire superlattice, and driven by a few-cycle circularly polarized optical field, reduces the symmetry of the states and allows for observing the Berry phase in the reciprocal space. Such an effect can be read-out with time- and angle-resolved photoelectron emission spectroscopy (Tr-ARPES).

Attosecond science relies on the use of intense, waveform-controlled, few-cycle laser pulses to control extreme nonlinear optical processes taking place within a fraction of an optical period. A number of techniques are available for retrieving the amplitude envelope and chirp of such few-cycle laser pulses. However, their full characterization requires detection of the absolute offset between the rapidly oscillating carrier wave and the pulse envelope, the carrier–envelope phase (CEP). So far, this has only been feasible with photoelectron spectroscopy, relying on complex vacuum set-ups. Here, we present a technique that enables the detection of the CEP of few-cycle laser pulses under ambient conditions. This is based on the CEP-dependence of directly measurable electric currents generated by the electric field of light in a metal–dielectric–metal nanojunction. The device holds promise for routine measurement and monitoring of the CEP in attosecond laboratories.

We propose an attosecond strong optical field interferometry in graphene which reveals the chirality of graphene without employing a magnetic field. A circularly polarized optical pulse with strong amplitude and femtosecond time scale causes the electron to circle in the reciprocal space through which it accumulates the dynamic phase along the closed trajectory as well as the nontrivial geometric phase known as Berry’s phase. The resulting interference fringes carry rich information about the electronic spectra and interband dynamics in graphene near the Dirac points. Our findings hold promises for the attosecond control and measurement of electron dynamics in condensed matters as well as understanding the topological nature of the two-dimensional Dirac materials.

We propose an interferometry in graphene's reciprocal space without a magnetic field, employing strong ultrafast circularly polarized optical pulses. The reciprocal space interferograms contain information on the electronic spectra and topological properties of graphene and on the waveform and circular polarization of the excitation optical pulses. These can be measured using angle-resolved photoemission spectroscopy (ARPES) with attosecond ultraviolet pulses. The predicted effects provide unique opportunities in fundamental studies of two-dimensional topological materials and in applications to future petahertz light-wave-driven electronics.

After the discovery of the spaser (surface plasmon amplification by stimulated emission of radiation), first proposed by Bergman and Stockman in 2003, it has become possible to deliver optical energy beyond the diffraction limit and generate an intense source of an optical field. The spaser is a nanoplasmonic counterpart of a laser. One of the major advantages of the spaser is its size: A spaser is a truly nanoscopic device whose size can be made smaller than the skin depth of a material to a size as small as the nonlocality radius ($\ensuremath{\sim}1$ nm). Recently, an electrically pumped graphene based nanospaser has been proposed that operates in the midinfrared region and utilizes a nanopatch of graphene as a source of plasmons and a quantum-well cascade as its gain medium. Here we propose an optically pumped nanospaser based on three-dimensional topological insulator (3D TI) materials, such as ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$, that operates at an energy close to the bulk band-gap energy $\ensuremath{\sim}0.3$ eV and uses the surface as a source for plasmons and its bulk as a gain medium. Population inversion is obtained in the bulk and the radiative energy of the exciton recombination is transferred to the surface plasmons of the same material to stimulate spasing action. This is truly a nanoscale spaser as it utilizes the same material for dual purposes. We show theoretically the possibility of achieving spasing with a 3D TI. As the spaser operates in the midinfrared spectral region, it can be a useful device for a number of applications, such as nanoscopy, nanolithography, nanospectroscopy, and semiclassical information processing.

This paper investigates the interaction of buckled Dirac materials (silicene and germanene) with ultrashort and ultrastrong optical pulses. Highly intensive few-cycle pulses strongly modify the electronic and optical properties of these two dimensional materials. Electron dynamics in such a short optical pulse is coherent and can be robustly controlled by altering the propagation direction, as well as the polarization angle of the pulse. The strong nonlinearity of the system for fields applied (~ V/A) causes the violation of the charge (C) and parity (P) symmetries, effectively reducing the system’s symmetry from hexagonal to triangular. Such symmetry violations are related to the electron transfer between the sublattices caused by the normal field component and result in nonreciprocity, optical rectification and the appearance of a cross current.

At the heart of ever growing demands for faster signal processing is ultrafast charge transport and control by electromagnetic fields in semiconductors. Intense optical fields have opened fascinating avenues for new phenomena and applications in solids. Because the period of optical fields is on the order of a femtosecond, the current switching and its control by an optical field may pave a way to petahertz optoelectronic devices. Lately, a reversible semimetallization in fused silica on a femtosecond time scale by using a few-cycle strong field (~1 V/Å) is manifested. The strong Wannier-Stark localization and Zener-type tunneling were expected to drive this ultrafast semimetallization. Wider spread of this technology demands better understanding of whether the strong field behavior is universally similar for different dielectrics. Here we employ a carrier-envelope-phase stabilized, few-cycle strong optical field to drive the semimetallization in sapphire, calcium fluoride and quartz and to compare this phenomenon and show its remarkable similarity between them. The similarity in response of these materials, despite the distinguishable differences in their physical properties, suggests the universality of the physical picture explained by the localization of Wannier-Stark states. Our results may blaze a trail to PHz-rate optoelectronics.

Dielectrics into semimetallic states by light field is studied. Despite different substances, the generality of semimetallization is observed, agreeing with theoretical prediction, taking intra and inter-transition into account.

We study experimentally and numerically the polarization sensitivity of quantum well infrared photodetectors coupled to a diffraction grid. The polarization extinction ratio of such system is determined by two factors: polarization sensitivity of the diffraction grid and the intrinsic polarization sensitivity of the photodetector itself. The combined effect of these factors result in non-monotonic dependence of the polarization extinction ratio on the parameters of the diffraction grid. By varying the grid parameters, i.e., increasing the height and tuning the grid period, a maximum value for the polarization extinction ratio can be achieved. Both front side and back side illuminations of the photodetector are studied. The strongest polarization sensitivity is achieved under front side illumination.

The possibility of enhancement of sensitivity of quantum well photodetectors by adding metallic diffraction coating on top of the dielectric layer of photodetectors is studied. With the grating the spatial distribution of the intensity of electromagnetic wave within the active region of the photodetector is highly non-uniform with the intensity variation over a few orders of magnitude within a period of the grating. This effect is due to the coupling of surface plasmon with incident electromagnetic wave. At terahertz frequencies the average intensity of the transmitted radiation wave through the grating strongly depends on the dielectric constant of metal.

We demonstrate that the tail of transmission distribution through a 1D disordered Anderson chain is a strong function of the correlation radius of the random potential, a, even when this radius is much shorter than the de Broglie wavelength, kF−1. The reason is that the correlation radius defines the phase volume of the trapping configurations of the random potential, which are responsible for the low-T tail. To see this, we perform the averaging over the low-T disorder configurations by first introducing a finite lattice spacing ∼a, and then demonstrating that the prefactor in the corresponding functional integral is exponentially small and depends on a even as a → 0. Moreover, we demonstrate that this restriction of the phase volume leads to a dramatic change in the shape of the tail of Open image in new window (ln T) from universal Gaussian in lnT to a simple exponential (in lnT) with the exponent depending on a. Severity of the phase-volume restriction affects the shape of the low-T disorder configurations, transforming them from almost periodic (Bragg mirrors) to periodically-sign-alternating (loose mirrors).

We report our theoretical study of the effect of metallic diffraction grating on the sensitivity of quantum dot photodetectors in terahertz frequency. We have found that the effect of diffraction grating is much stronger for s-polarization than for p-polarization. For s-polarization the sensitivity of photodetectors can be enhanced by metallic diffraction grating by a few orders of magnitude. Due to strongly inhomogeneous distribution of electromagnetic field the quantum dots should be placed at special points, i.e. hot spots, where the field intensity is maximum.

We theoretically show that buckled two-dimensional graphene-like materials (silicene and germanene) subjected to a femtosecond strong optical pulse can be controlled by the optical field component normal to their plane. In such strong fields, these materials are predicted to exhibit non-reciprocal reflection, optical rectification and generation of electric currents both parallel and normal to the in-plane field direction. Reversibility of the conduction band population is also field- and carrier-envelope phase controllable. There is a net charge transfer along the material plane that is also dependent on the normal field component. Thus a graphene-like buckled material behaves analogously to a field-effect transistor controlled and driven by the electric field of light with subcycle (femtosecond) speed., 9 pages, six figures, 53 references

For graphene interacting with a few-fs intense optical pulse, we predict unique and rich behavior dramatically different from three-dimensional solids. Quantum electron dynamics is shown to be coherent but highly nonadiabatic and effectively irreversible due to strong dephasing. Electron distribution in reciprocal space exhibits hot spots at the Dirac points and oscillations whose period is determined by nonlocality of electron response and whose number is proportional to the field amplitude. The optical pulse causes net charge transfer in the plane pf graphene in the direction of the instantaneous field maximum at relatively low fields and in the opposite direction at high fields. These phenomena promise ultrafast optoelectronic applications with petahertz bandwidth.

We report on the effect of temperature fluctuations on the midinfrared electroluminescence from a cascade of coupled AlInAs quantum dots and GaAs quantum wells. The observed line width is significantly broadened with increasing temperature. We then present our theoretical results on homogeneous line broadening due to temperature fluctuations for our experimental system. Our numerical simulations clearly indicate that, temperature fluctuations can account for the observed finite width of the emission lines at high-temperatures.