Dissipative Electron Transport Research Articles

New families of quantum spin Hall insulators with rashba effect in functionalized InBi monolayers

Because quantum spin Hall (QSH) insulators with dissipative electron transport properties have broad application prospect in the field of quantum devices, QSH insulators have aroused great research enthusiasm and many ideal QSH insulators are predicted successfully. Based on density functional calculations, we predict that new families of functionalized InBi monolayers, H–InBi-X (X = F, Cl, Br, I), to be QSH insulators. We find that the pristine InBi monolayer that is simultaneously hydrogenated and halogenated has a maximum band gap of 0.49 eV while preserving the untrivial topological properties, which is large enough for room-temperature applications. Because of the absence of inversion symmetry, the Rashba SOC effect occurs in the band structure and the SOC not only opens the bandgaps but also leads to the band inversion. In addition, the topological properties of these monolayers can survive a wide range of external strain from −6% to 6%. Our findings enrich the inversion-asymmetry topological materials and provide a reliable reference for designing QSH insulators at room temperature.

Landauer Formula for a Superconducting Quantum Point Contact.

We generalize the Landauer formula to describe the dissipative electron transport through a superconducting point contact. The finite-temperature, linear-in-bias, dissipative dc conductance is expressed in terms of the phase- and energy-dependent scattering matrix of the Bogoliubov quasiparticles in the quantum point contact. The derived formula is also applicable to hybrid superconducting-normal structures and normal contacts, where it agrees with the known limits of Andreev reflection and normal-state conductance, respectively.

Random phonon model of dissipative electron transport in nanowire MOSFETs

A method for quantum transport simulations of nanowire (NW) field-effect transistors (FETs) with inelastic electron---phonon scattering processes incorporated is presented in this paper. The microscopic device Hamiltonian with realistic phonon spectrum and electron---phonon interaction is transformed into an equivalent low-dimensional transport model with discrete random phonon modes. The electron---phonon coupling constants are optimized in order to reproduce the inelastic scattering effects. Small size of the model and special form of the inelastic self-energy terms in the NEGF formalism make it a powerful tool to study dissipative transport in realistic NW transistors. The utility of the method is demonstrated by computing inelastic transport characteristics in Si NW FETs.

Dissipative transport in superlattices within the Wigner function formalism

We employ the Wigner function formalism to simulate partially coherent, dissipative electron transport in biased semiconductor superlattices. We introduce a model collision integral with terms that describe energy dissipation, momentum relaxation, and the decay of spatial coherences (localization). Based on a particle-based solution to the Wigner transport equation with the model collision integral, we simulate quantum electronic transport at 10 K in a GaAs/AlGaAs superlattice and accurately reproduce its current density vs field characteristics obtained in experiment.

Supercurrent dephasing by electron-electron interactions

We demonstrate that in sufficiently long diffusive superconducting-normal-superconducting ($\mathit{SNS}$) junctions dc Josephson current is exponentially suppressed by electron-electron interactions down to zero temperature. This suppression is caused by the effect of Cooper pair dephasing which occurs in the normal metal and defines a new fundamental length scale ${L}_{\ensuremath{\varphi}}$ in the problem. This length is fully consistent with that derived earlier from the analysis of dissipative electron transport across $\mathit{NS}$ interfaces at subgap energies. Provided the temperature length exceeds ${L}_{\ensuremath{\varphi}}$ this dephasing length can be conveniently extracted from equilibrium measurements of the Josephson current.

Thermal probing of energy dissipation in current-carrying carbon nanotubes

The temperature distributions in current-carrying carbon nanotubes have been measured with a scanning thermal microscope. The obtained temperature profiles reveal diffusive and dissipative electron transport in multiwalled nanotubes and in single-walled nanotubes when the voltage bias was higher than the 0.1–0.2 eV optical phonon energy. Over 90% of the Joule heat in a multiwalled nanotube was found to be conducted along the nanotube to the two metal contacts. In comparison, about 80% of the Joule heat was transferred directly across the nanotube-substrate interface for single-walled nanotubes. The average temperature rise in the nanotubes is determined to be in the range of 5–42 K per microwatt Joule heat dissipation in the nanotubes.

Computationally efficient method for scattering device simulation in nanoscale MOSFETs

A computationally efficient and rigorous simulation method for treating dissipative electron transport in nanoscale, thin body, fully depleted SOI MOSFETs quantum-mechanically has been described. Within the non-equilibrium Green function (NEGF) formalism, scattering can be simply treated on the base of Büttiker probes. The probe strength is related to the low-field mobility, which depends on the electron subband and longitudinal position. Therefore, the low-field mobility for every subband at every position along the channel has been calculated using the eigenenergies and wave functions along the confinement direction and the Fermi level along the channel per self-consistent loop. As a result, the effect of scattering can be rigorously treated under the NEGF formalism. Our model has been applied to nanoscale n-channel double-gate MOSFETs and the results have been compared to those calculated with the conventional model. Moreover, the dependence of the output current on the silicon body thickness for the case with scattering has been investigated.

An Accurate and Computationally Efficient Method for Device Simulation with Scattering in Nanoscale Double-Gate Metal–Oxide–Semiconductor Transistors

An accurate and computationally efficient simulation method for quantum-mechanically treating dissipative electron transport in nanoscale double-gate metal–oxide–semiconductor field-effect transistors (DG MOSFETs) has been described. Within the nonequilibrium Green function formalism (NEGF), scattering can be simply treated on the base of Büttiker probes. The probe strength is related to the low-field mobility, which depends on the electron subband and longitudinal position. Therefore, the low-field mobility for every subband at every position along the channel has been calculated using the eigenenergies and wavefunctions along the confinement direction and the Fermi level along the channel per self-consistent loop. As a result, the effect of scattering can be rigorously treated under the NEGF formalism.

A simple quantum mechanical treatment of scattering in nanoscale transistors

We present a computationally efficient, two-dimensional quantum mechanical simulation scheme for modeling dissipative electron transport in thin body, fully depleted, n-channel, silicon-on-insulator transistors. The simulation scheme, which solves the nonequilibrium Green’s function equations self consistently with Poisson’s equation, treats the effect of scattering using a simple approximation inspired by the “Büttiker probes,” often used in mesoscopic physics. It is based on an expansion of the active device Hamiltonian in decoupled mode space. Simulation results are used to highlight quantum effects, discuss the physics of scattering and to relate the quantum mechanical quantities used in our model to experimentally measured low field mobilities. Additionally, quantum boundary conditions are rigorously derived and the effects of strong off-equilibrium transport are examined. This paper shows that our approximate treatment of scattering, is an efficient and useful simulation method for modeling electron transport in nanoscale, silicon-on-insulator transistors.

Features of the dissipative electron transport near the boundary in the system Al(N)-In(S)

The temperature behavior of the coherent electron transport that arises in the presence of Andreev reflections is studied near the boundary of a hybrid system consisting of aluminum (N) and indium (S). The qualitative change of the temperature behavior upon changes in the electron mean free path lel as a result of the elastic deformation of the sample is observed for the first time on the same sample, at probes mounted in the normal region at fixed distances and from the boundary. As the temperature is lowered, the measured effective resistance decreases for lel ≪ L1, 2 and increases in a certain temperature region in which lel ∼ L1, 2. It is shown that phenomena of this kind correspond to quantum-interference features in the scattering of coherent electronic and Andreev hole excitations on elastic centers.

A re-evaluation of the ATP :NADPH budget during C3 photosynthesis: a contribution from nitrate assimilation and its associated respiratory activity?

The purpose of this review in reanalysing the ATP :reluctant balance in illuminated leaf cells is to stress that photosynthesis in vivo does not involve CO2 fixation alone, but embraces other processes, chief among which is N assimilation. Prior to the demonstration of CO2 fixation and photophosphorylation by isolated chloroplasts, the mitochondria were thought likely to provide all the ATP required for CO2 fixation (discussed in Arnon et al., 1954). During the 1960s, the development of techniques for the isolation of chloroplasts able to fix CO2 at rates approaching those of the parent tissue induced a paradigm shift, leading to the establishment of a dominant (if not unanimous) view that chloroplasts in vivo must by themselves meet all their ATP requirements. More recent studies, however, indicate that the reality lies somewhere between these two extremes. The present work places emphasis on the integrated nature of photosynthesis and proposes that much of the respiratory ATP necessary for whole cell photosynthesis may be generated during the production of C skeletons for N assimilation. Rather than considering dissipative electron transport pathways as necessary to uncouple respiratory precursor synthesis from ATP production, the present analysis emphasizes the metabolic value of ATP produced during N-linked respiration, with cellular ATP supply being tailored to ATP demand.

Ballistic and dissipative electron transport in semiconductor superlattices

Ballistic electron transport is used to study the transmittance of GaAs/GaAlAs superlattices. In a three terminal device an energy tunable electron beam is injected via a tunneling barrier into an undoped superlattice and the transmitted current is measured as a function of the injector energy. Significant increase of the collector current is observed due to miniband conduction in the GaAs/AlGaAs superlattice. At flat band condition the transfer ratio α= I C/ I E can be used to probe miniband position and miniband widths. Measuring the transfer ratio of superlattices at various bias conditions, a significant decrease of the miniband transmission with increasing electric field is observed, which can be attributed to the transition between coherent and incoherent transport in these superlattices. The results agree very well with theory.

Electromagnetic wave effects on electron–phonon scattering in semiconductor quantum wires

The dissipative electron transport in the free-standing semiconductor wire in the presence of electromagnetic wave is considered. The non-Markovian Langevin-like equations describing both kinetics and fluctuations of an electron are obtained. It is shown that in the 1D case electromagnetic wave influences on electron–phonon interaction drastically that increases the electron mobility. Phonon emission spectrum and energy loss rate are found.

Analysis of electron transport in a two-dimensional structure using quantal trajectories

Ballistic and dissipative electron transport through a two-dimensional geometry is studied in the de Broglie-Bohm quantal trajectory model. The dissipative effect, incorporated to simulate inelastic scattering, is introduced via an imaginary potential term in the Hamiltonian. The relation between the conductance and the local behaviour of the quantal trajectories is discussed. The vortex-like structure of the de Broglie-Bohm trajectories in the vicinity of wavefunction nodes is studied.

Dissipative electron transport through Andreev interferometers

We consider the conductance of an Andreev interferometer, i.e., a hybrid structure where a dissipative current flows through a mesoscopic normal (N) sample in contact with two superconducting (S) "mirrors". Giant conductance oscillations are predicted if the superconducting phase difference $\phi$ is varied. Conductance maxima appear when $\phi$ is on odd multiple of $\pi$ due to a bunching at the Fermi energy of quasiparticle energy levels formed by Andreev reflections at the N-S boundaries. For a ballistic normal sample the oscillation amplitude is giant and proportional to the number of open transverse modes. We estimate using both analytical and numerical methods how scattering and mode mixing --- which tend to lift the level degeneracy at the Fermi energy --- effect the giant oscillations. These are shown to survive in a diffusive sample at temperatures much smaller than the Thouless temperature provided there are potential barriers between the sample and the normal electron reservoirs. Our results are in good agreement with previous work on conductance oscillations of diffusive samples, which we propose can be understood in terms of a Feynman path integral description of quasiparticle trajectories.

Comparison between the relaxation time approximation and the Boltzmann collision operator for simulation of dissipative electron transport in resonant tunnelling diodes

Carrier scattering in the Wigner formalism has been introduced for the simulation of dissipative electron transport in resonant tunnelling diodes. Two approaches have been considered: the relaxation time approximation and the Boltzmann collision operator. The relaxation time and transition rates have been evaluated and have been introduced in the discretized version of the Liouville equation to obtain the Wigner distribution function and the current density. Not only phonon scattering, but also ionized impurity scattering has been accounted for in both approaches. We have compared the two scattering models on the basis of the I–V characteristics which have been simulated under various temperature and doping conditions. The results clearly reveal a lower current peak in the Boltzmann collision operator approach. Since the results of both approaches are divergent and since no clear computation advantages are obtained from the relaxation time approximation, we prefer the use of the more realistic Boltzmann collision operator for the simulation of dissipative electron transport in resonant tunnelling diodes.

Crossover between dissipative and nondissipative electron transport in metal wires.

Electron transport in one-dimensional metal wires of different length is shown to change from dissipative to nondissipative when the electron-phonon relaxation length becomes equal to the wire length. The crossover provides the first direct measurement of the energy relaxation length in metal wires which is found to have an inverse cube temperature dependence. In the dissipationless regime the electron energy is shown to be linearly related to the voltage applied across the wire.

Unified description of coherent and dissipative electron transport.

We apply the Landauer-B\"uttiker theory of dc electron transport to a chain of scatterers, which are coupled to an external heat bath. In this approach, coherent and dissipative transport are treated in a unified manner, and the suppression of quantum coherence effects for increasing coupling with the heat bath can be described. In particular, we find that the resonant behavior of the conductance with respect to the Fermi wave vector disappears gradually with increasing coupling. For intermediate coupling, resonance effects are only found for sufficiently small samples. They disappear asymptotically with increasing sample size. The characteristic length for this dephasing effect corresponds to the mean free path, which is derived from the exponential decay of the transmission coefficient in the presence of inelastic scattering.