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Very recently, half-hydrogenated germanene has been achieved in an experiment. In this paper, we investigate the effects of tetracyanoquinodimethane (TCNQ) molecular adsorption and strain on the electronic properties of half-hydrogenated germanene through first-principles. As an electron-acceptor molecule, TCNQ is exploited to non-covalently functionalize the half-hydrogenated germanene. However, this physical adsorption induces a ferromagnetic semiconductor–metal transition in half-hydrogenated germanene due to charge transfer from the substrate to the TCNQ molecule. More importantly, the superstructure of half-hydrogenated germanene/TCNQ is extremely sensitive to biaxial tensile strain. Under the biaxial tensile strain of 0.25%, the ferromagnetic semiconductor–metal transition induced by molecular adsorption can surprisingly be overturned. Meanwhile, a strong p-type doping is exhibited. Remarkably, it would return from a ferromagnetic semiconductor to a metal again when the biaxial tensile strain increases to 1.5%. Our analysis based on the structural and electronic properties of half-hydrogenated germanene/TCNQ indicates that such metal–semiconductor–metal transition in half-hydrogenated germanene/TCNQ under biaxial tensile strain may originate from the strong local deformation, resulting in the energy of the valence band maximum decreasing below or increasing above the Fermi level. [ABSTRACT FROM AUTHOR]

We analyze a phase-sensitive contribution to the oscillating magnetoresistance induced by the combined driving of two microwave fields having commensurate frequencies ω1 and ω2 (m1ω1+m2ω2=0 for at least a set of nonzero integers m1 and m2), based on the balance-equation approach to magnetotransport for high-density two-dimensional electron systems. This commensurate oscillating photoresistance not only depends on the frequencies and polarizations of both microwaves, but varies drastically when changing the relative phases of two incident radiation fields. It shows up most significantly in the case of ω2/ω1=3 and may lead to a phase-controllable change of more than a factor of two in the total magnetoresistivity in the vicinity of ω1/ωc=1.5 and 2.5 (ωc is the cyclotron frequency), when both radiation fields are linearly x-direction polarized. [ABSTRACT FROM AUTHOR]

We analyze the effects of a distortion of the nuclear potential of a molecular quantum dot (QD) as well as a shift in its equilibrium position on nonequilibrium-vibration-assisted tunneling through the QD with a single level ([variant_greek_epsilon]d) coupled to the vibrational mode. For this purpose, we derive an explicit analytical expression for the Franck–Condon (FC) factor for a displaced-distorted oscillator surface of the molecule and establish rate equations in the joint electron-phonon representation to examine the current-voltage characteristics and zero-frequency shot noise and skewness as well. Our numerical analysis shows that the distortion has two important effects. The first one is that it breaks the symmetry between the excitation spectra of the charge states, leading to asymmetric tunneling properties with respect to [variant_greek_epsilon]d>0 and [variant_greek_epsilon]d<0. Second, distortion (frequency change in the oscillator) significantly changes the voltage-activated cascaded transition mechanism and consequently gives rise to a different nonequilibrium vibrational distribution from that of the case without distortion. Taken in conjunction with strongly modified FC factors due to distortion, this results in some new transport features: the appearance of strong negative differential conductance even for a single-level QD with symmetric tunnel couplings, a giant Fano factor even for a molecule with an extremely weak electron-phonon interaction, and enhanced skewness that can have a large negative value under certain conditions. [ABSTRACT FROM AUTHOR]

We present a kinetic equation approach to investigate dc transport properties of graphene in the diffusive regime considering long-range electron-impurity scattering. In our study, the effects of interband correlation (or polarization) on conductivity are taken into account. We find that the conductivity contains not only the usual term inversely proportional to impurity density Ni but also an anomalous term that is linear in Ni. This leads to a minimum in the density dependence of conductivity when the electron density Ne is equal to a finite critical value Nc. The effects of various scattering potentials on the conductivity minimum are also analyzed. Using typical experimental parameters, we find that for random-phase-approximation–screened electron-impurity scattering, the minimum conductivity is about 4.42e2/h when Ne≈0.11Ni, and the conductivity varies almost linearly with the electron density for Ne>Ni. [ABSTRACT FROM AUTHOR]

We examine the shot noise spectrum properties of coherent resonant tunneling in coupled quantum dots (CQDs) in both series and parallel arrangements by means of quantum rate equations and MacDonald’s formula. Our results show that for a series-CQD with a relatively high dot-dot hopping Ω and Ω/Γ>=1 (Γ denotes the dot-lead tunnel-coupling strength), the noise spectrum exhibits a dip at the Rabi frequency 2Ω in the case of noninteracting electrons, but the dip is supplanted by a peak in the case of strong Coulomb repulsion; furthermore, it becomes a dip again for a completely symmetric parallel-CQD by tuning the enclosed magnetic flux. [ABSTRACT FROM AUTHOR]

Reports on a study which analyzed the scattering for the intra- and intersubband transitions of electrons in a GaAs/AlAs quantum well with a central AlAs thin layer assisted by the emission and absorption of optical phonon modes. Application of transversal electric field through the structure; Frohlich interaction and electron mobility; Antisymmetric interface phonon modes.

Presents a study which developed a non-Boltzmann theory of a steady-state transport for two-dimensional systems in a strong electric field which includes a force- and an energy-balance equation. Method of the study; Results and discussion; Conclusion.

Proposes balance equations for high-field electron transport in nonparabolic multiband semiconductors. Relation between electron energy and lattice wave vector; Description of a balance equation for multiband systems; Findings of the study.

Deals with a study which investigated Bragg scattering and effective force-balance equations in superlattice miniband transport. Background to the study; Background on the Büttiker-Thomas momentum balance equation; Details on the acceleration and energy balance equations.

Investigates the linear and nonlinear miniband electron transport through a laterally confined superlattice using the balance-equation theory. Acceleration and energy-balance equations; Calculation of the linear and nonlinear properties of GaAs/AlAs superlattices; Linear mobilities.

Presents a study which examined linear and nonlinear characteristics of superconductor superlattice perpendicular conduction. Linear mobilities from the balance-equation theory; Comparisons between theories and experiments; Conclusions.

Microwave-induced magnetoresistance oscillations in two-dimensional electron systems are examined from a photon-assisted transport scheme with short-range impurity scatterings. Analytical results at high filling factors strongly support early considerations and the recent experimental observation that the temperature dependence of the oscillation amplitude is exponential and originates primarily from the single-particle lifetime. [ABSTRACT FROM AUTHOR]

Nonlinear magnetotransport of a microwave-irradiated high-mobility two-dimensional electron system under a finite direct current excitation is analyzed using a dc-controlled scheme with photon-assisted transition mechanism. The predicted amplitudes, extrema, and nodes of the oscillatory differential resistance versus the magnetic field and the current density are in excellent agreement with the recent experimental observation [Hatke et al. Phys. Rev. B 77, 201304(R) (2008)]. [ABSTRACT FROM AUTHOR]

Motivated by a recent experiment [S. O. Valenzuela and M. Tinkham, Nature (London) 442, 176 (2006)], the authors present a quantitative microscopic theory to investigate the inverse spin-Hall effect with spin injection into aluminum considering both intrinsic and extrinsic spin-orbit couplings using the orthogonalized-plane-wave method. Their theoretical results are in good agreement with the experimental data. It is also clear that the magnitude of the anomalous Hall resistivity is mainly due to contributions from extrinsic skew scattering. [ABSTRACT FROM AUTHOR]

Magnetoresistance oscillations in two-dimensional electron systems driven simultaneously by a strong direct current and a microwave irradiation are analyzed within a unified microscopic scheme treating both excitations on an equal footing. The microwave-induced resistance oscillations are described by a parameter εω proportional to the radiation frequency, while the dc-induced resistance oscillations are governed by a parameter εj proportional to the current density. In the presence of both a microwave radiation and a strong dc, the combined parameter εω+εj is shown to control the main resistance oscillations, in agreement with the recent measurement [Zhang et al., Phys. Rev. Lett. 98, 106804 (2007)]. [ABSTRACT FROM AUTHOR]

The authors analyze resonant tunneling subject to a nonadiabatic time-dependent bias voltage through an asymmetric single molecular quantum dot with coupling between the electronic and vibrational degrees of freedom using a Tien-Gordon-type rate equation. The results clearly exhibit the appearance of photon-assisted satellites in the current-voltage characteristics and the elimination of hot-phonon-induced negative differential conductance with increasing ac driving amplitude for an asymmetric system. This can be ascribed to an ac-induced suppression of unequilibrated (hot) phonons in an asymmetric system. [ABSTRACT FROM AUTHOR]

Electric current-induced magnetoresistance oscillations recently discovered in two-dimensional electron systems are analyzed using a microscopic scheme for nonlinear magnetotransport direct controlled by the current. The magnetoresistance oscillations are shown to result from drift-motion assisted electron scatterings between Landau levels. The theoretical predictions not only reproduce all the main features observed in the experiments but also disclose other details of the phenomenon. [ABSTRACT FROM AUTHOR]

The magnetoresistance oscillations in high-mobility two-dimensional electron systems induced by two radiation fields of frequencies 31 and 47 GHz are analyzed in a wide magnetic-field range down to 100 G, using the balance-equation approach to magnetotransport for high-carrier-density systems. The frequency mixing processes are shown to be important. The predicted peak positions, relative heights, radiation-intensity dependence and their relation with monochromatic resistivities are in good agreement with recent experimental finding [M. A. Zudov et al., Phys. Rev. Lett. 96, 236804 (2006)]. [ABSTRACT FROM AUTHOR]

Recently discovered new structures and zero-resistance states outside the well-known oscillations are demonstrated to arise from multiphoton assisted processes, by a detailed analysis of microwave photoresistance in two-dimensional electron systems under enhanced radiation. The concomitant resistance dropping and the peak narrowing observed in the experiments are also reproduced. We show that the radiation-induced suppression of average resistance comes from virtual photon effect and exists throughout the whole magnetic field range. [ABSTRACT FROM AUTHOR]

It is shown that a finite spin-Hall current can be induced by applying an in-plane magnetic field in a diffusive two-dimensional electron system with the Rashba and Dresselhaus spin-orbit couplings subjected to a dc electric field. The spin-Hall conductivity depends not only on the strength and direction of the magnetic field, but also strongly depends on the form of the scattering potential. It can be negative or positive in the case of remote impurity scattering, but essentially positive in the case of short-range scattering. [ABSTRACT FROM AUTHOR]

Recently discovered modulations of Shubnikov–de Haas oscillations in microwave-irradiated two-dimensional electron systems are shown to arise from electron heating induced by the radiation. The electron temperature, obtained by balancing the energy absorption from the microwave field and the energy dissipation to the lattice through realistic electron-phonon couplings, exhibits resonance. The modulation of the Shubnikov–de Haas oscillation and the suppression of magnetoresistance are demonstrated together with microwave-induced resistance oscillation, in agreement with experimental findings. [ABSTRACT FROM AUTHOR]

Far infrared photoresponse of magnetoresistivity ΔR[sub xx] of two-dimensional electron systems is investigated theoretically at high temperatures. Photon-assisted impurity and phonon scatterings, rather than the electron heating, are shown to be the dominant mechanisms for high-temperature photoresponse at cyclotron resonance. Based on the theory developed for electron magnetotransport driven by intense terahertz radiations, we have calculated the far infrared photoresistivity of a GaAs/AlGaAs heterostructure at temperature T=150 K, predicting notable cyclotron resonance of ΔR[sub xx], in agreement with the experimental finding. Contrary to low temperature case, where the electron heating is almost solely responsible for the cyclotron resonance of ΔR[sub xx], at T=150 K electron-heating contribute at most a small fraction of the total response. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have analyzed spatio-temporal current patterns and current–voltage characteristics of negative-effective-mass (NEM) p[sup +]pp[sup +] diodes driven by dc bias and terahertz (THz) electromagnetic radiation. Interesting nonlinear dynamics are presented, including current synchronization, frequency doubling, and transition to chaos. Discussions of suppressing possible chaos in NEM semiconductor devices are included. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on a theoretical investigation of power spectrum dynamics in negative-effective-mass (NEM) p[sup +]pp[sup +] oscillators under the influence of terahertz (THz) electromagnetic radiation. Possible types of transport states (periodic or chaotic) and transitions between them are examined with the intensity and frequency of the radiation as controlling parameters. When the driving frequency is fixed to the self-oscillating frequency times the inverse Golden ratio, the resulting power spectrum pattern displays a very complex mosaic scenario with a self-similar emergence of high-order mixing frequencies. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present a theoretical study on the angular and frequency distributions of the acoustic and optic-phonon generation by hot electrons during the terahertz-driven transport in a GaAs-based quantum well. Based on the detailed solution of the nonlinear balance equations in the presence of an oscillating electric field of arbitrary strength, we find that, when the system is exposed to an intense terahertz radiation, emissions of acoustic and optic phonons are significantly enhanced, especially along the polarized direction of the electric field. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]