Dynamic conductance of a ballistic quantum wire

Within the framework of exact linear response theory, we derive a general formula, with which the dynamic conductance of mesoscopic system can be determined in the absence of Coulomb interaction. In addition, we present a solution to the problem of current partition in the system. These allow the derivation of dynamic conductance in time-dependent case. As a natural consequence, the current (charge) conservation and gauge invariance conditions are fulfilled. To give an example, we discuss the dynamic conductance of a ballistic quantum wire, and the effect of contacts on the conductance is also discussed.     

Conductance of a quantum wire in a longitudinal magnetic field

We examine the ballistic conductance of a quantum wire in a parallel magnetic field in the presence of several impurities and derive analytic expressions for the transmission coefficient and the conductance in such a system. We show that scattering by impurities leads to a number of sharp peaks near the thresholds of the conductance quantization steps. The number of such peaks is determined by the distance between the impurities and the energy of the scattered particle. We also study the conductivity of a quantum wire in the region where the transport mechanism is diffusive. The conductivity is examined for the case in which charge carriers are scattered by randomly distributed point impurities. We study Shubnikov-de Haas oscillations in such a system. The general oscillation pattern consists of broad minima separated by irregularly spaced sharp peaks of the burst type. Zh. éksp. Teor. Fiz. 113, 1376–1396 (April 1998)     

Conductance of a quantum wire in the Wigner-crystal regime

We study the effect of Coulomb interactions on the conductance of a single-mode quantum wire connecting two bulk leads. When the density of electrons in the wire is very low, they arrange in a finite-length Wigner crystal. In this regime the electron spins form an antiferromagnetic Heisenberg chain with an exponentially small coupling J. An electric current in the wire perturbs the spin chain and gives rise to a temperature-dependent contribution of the spin subsystem to the resistance. At low temperature TJ the spin effect reduces the conductance to e2/h.     

Conductance of the elliptically shaped quantum wire

The conductance of a ballistic elliptically shaped quantum wire is investigated theoretically. It is shown that the effect of the curvature results in a strongly oscillating dependence of the conductance on the applied bias.     

Fano factor reduction on the 0.7 conductance structure of a ballistic one-dimensional wire

We have measured the nonequilibrium current noise in a ballistic one-dimensional wire which exhibits an additional conductance plateau at 0.7x2e(2)/h. The Fano factor shows a clear reduction on the 0.7 structure, and eventually vanishes upon applying a strong parallel magnetic field. These results provide experimental evidence that the 0.7 structure is associated with two conduction channels that have different transmission probabilities.     

Spin-polarized transport in multiterminal silicene nanodevices

The spin-polarized transport properties of multiterminal silicene nanodevices are studied using the tight binding model and Landauer–Buttier approach. We propose a four-terminal 2-shaped junction device and two types of three-terminal T-shaped junction devices, which are made of the crossing of a zigzag and an armchair silicene nanoribbon. If the electrons are injected into the metallic lead, the near-perfect spin polarization with 100% around the Fermi energy can be achieved easily at the other semiconducting leads. Thus the multiterminal silicene nanodevices can act as controllable spin filters.     

Phase states of multiterminal mesoscopic normal-metal-superconductor structures

We study a mesoscopic normal-metal structure with four superconducting contacts, two of which are joined into a loop. The structure undergoes transitions between three (meta)stable states, with different phase configurations triggered by nonequilibrium conditions. These transitions result in spectacular changes in the magnetoresistance. We find a qualitative agreement between the experiments and a theory based on the quasiclassical Keldysh formalism.     

Transport theory of multiterminal hybrid structures

We derive a microscopic transport theory of multiterminal hybrid structures in which a superconductor is connected to several spin-polarized electrodes. We discuss the non-perturbative physics of extended contacts, and show that such contacts can be well represented by averaging out the phase of the electronic wave function. The intercontact Andreev reflection and elastic cotunneling conductances are identical if the phase can be averaged out, namely in the presence of at least one extended contact. The maximal conductance of a two-channel contact is proportional to (e ²/h)(a ₀/D)²exp[-D/ξ(ω^*)], where D is the distance between the contacts, a₀ the lattice spacing, ξ(ω) is the superconducting coherence length, and ω^* is the cross-over frequency between a perturbative regime ( ω < ω^*) and a non perturbative regime ( ω^* < ω < Δ). Received 18 June 2001 and Received in final form 17 January 2002     

An optical-fiber multiterminal data system for aircraft

Abstract

As a result of a study on the potential of optical-fiber multiterminal data systems for avionics, a design approach has been chosen that is expected to be a suitable basis for a wide range of applications. This is a time division multiplexing system, which has features of being highly immune to problems of optical loss and multipath effects in optical highways having redundant paths, and of avoiding the need for any master terminal. This system approach is tailored to characteristics of optical fibers, and should lead to good integrity and ruggedness. A breadboarded model of a terminal has been demonstrated, and the construction of functional models is currently under way.     

Proximity effect in multiterminal hybrid structures

We consider the proximity effect in multiterminal ferromagnet/superconductor (FSF) hybrid structures in which two or three electrodes are connected to a superconductor. We show that two competing effects take place in these systems: (i) pair breaking effects due to the response to the exchange field induced in the superconductor; (ii) a reduction of the superconducting order parameter at the interface that takes place already in NS junctions. We focus on this second effect that dominates if the thickness of the S layer is small enough. We consider several single-channel electrodes connected to the same site. We calculate the superconducting order parameter and the local density of state (LDOS). With two ferromagnetic electrodes connected to a superconductor we find that the superconducting order parameter in the ferromagnetic alignment is larger than the superconducting order parameter in the antiferromagnetic alignment ( > ), in agreement with [Eur. Phys. J. B 25, 373 (2002)]. If a third spin polarized electrode is connected to a superconductor we find that - can change sign as the transparency of the third electrode increases. This can be understood from the fact that the superconducting order parameter is reduced if pair correlations among the ferromagnetic electrodes increase. If the two ferromagnetic electrodes are within a finite distance we find Friedel oscillations in the Gorkov function but we still obtain > .     

Macroscopic quantum interference effects in superconducting multiterminal microstructures

We review the macroscopic quantum phenomena in superconducting microstructures based on multiterminal junctions. The multiterminal Josephson junction presents a system in which the weak coupling takes place between several massive superconducting banks (terminals). Compared with the conventional (two-terminal) junctions such systems have additional degrees of freedom and a corresponding set of control parameters, preset transport currents and (or) applied magnetic fluxes. The general phenomenological theory of multiterminal Josephson junctions is presented. The specific multichannel interference effects (studied theoretically and experimentally) are described for two microstructures: the four-terminal SQUID and a system consisting of two weakly coupled superconducting rings.     

Microwave response of a ballistic quantum dot

The microwave response (photovoltage and photoconductance) of a lateral ballistic quantum dot made of a high-mobility two-dimensional electron gas in an AlGaAs/GaAs heterojunction has been studied experimentally in the frequency range of 110–170 GHz. It has been found that the asymmetry of the photovoltage with respect to the sign of the magnetic field has mesoscopic character and depends on both the magnetic field and the microwave power. This indicates the violation of the Onsager reciprocity relations regarding the electron-electron interactions in the mesoscopic photovoltaic effect. A strong increase in the conductance of the quantum dot induced by the microwave radiation and unrelated to heating, as well as the microwave-induced magneto-oscillations, has been discovered.     

Andreev Conductance of a ferromagnet-superconductor point contact

Based on the boundary conditions derived for quasiclassical Green’s functions, a theory of Andreev reflection in ferromagnet-superconductor point contacts is constructed. From a comparison with experimental data, the polarization of the conduction band was estimated for a number of ferromagnetic materials used in experiments on Andreev spectroscopy.     

环形聚乙炔分子桥的电导研究

我们选择了由40个CH基团组成的环形聚乙炔链作为分子桥,基于Landauer-Buttiker理论,利用求解散射波函数的方法,研究了这种环状聚乙炔分子桥与金属多端连接的电导随能量的变化关系.结果表明,在给定入射端的条件下,电导在正负能量上是对称的,当各个端口满足旋转对称性时,相对于入射端对称的两个出射端的电导相同.当分子桥耦合较弱时,电导对能量的变化相当敏感.     

Acoustoelectric current through a ballistic microconstriction

The behavior of an acoustoelectric current through a three-dimensional quantum microconstriction placed in a longitudinal uniform magnetic field is studied theoretically in the ballistic transport regime. The oscillation periods of the acoustoelectric current are studied in detail as functions of the chemical potential and the magnetic field induction. The temperature effect is taken into account. It is shown that the acoustoelectric current as a function of the chemical potential can exhibit a steplike behavior. The limits for the existence of a steplike structure are determined.     

Circuit theory for full counting statistics in multiterminal circuits

We propose a theory that treats the current, noise, and, generally, the full current statistics of electron transfer in a mesoscopic system in a unified, simple, and efficient way. The theory appears to be a circuit theory of 2 x 2 matrices associated with Keldysh Green functions. We illustrate the theory by considering the big fluctuations of currents in various three-terminal circuits.     

Nonlinear magnetoconductance of a classical ballistic system

We study nonlinear transport through a classical ballistic system accounting for the Coulomb interaction between electrons. The joint effect of the applied bias V and magnetic field H on the electron trajectories results in a component of the nonlinear current I(V,H) which lacks the H-->-H symmetry: deltaI=alpha(cl)V(2)H. At zero temperature the magnitude of alpha(cl) is of the same order as that arising from the quantum interference mechanism. At higher temperatures the classical mechanism is expected to dominate due to its relatively weak temperature dependence.