Transport Properties Of Quantum Wires Research Articles

Fano effect in quasi‐one‐dimensional wires with short‐ or finite‐range impurities

AbstractIn various calculations on the transport properties of quantum wires with impurities, transmission resonances have been found that exhibit the asymmetric Fano line shape. However, short‐ and finite‐range impurities may lead to distinctly different behavior of these resonances. It is shown here that increasing the strength of a shortrange impurity causes a linear increase of the asymmetry parameter and a monotonic decrease of the resonance width. On the other hand, increasing the strength of a finite‐range impurity causes a transformation of an asymmetric Fano resonance into a symmetric antiresonance and subsequently into an “inverted” Fano resonance. This is reflected in an oscillatory behavior of the asymmetry parameter and resonance width. The interference effects that cause this behavior are identified using a coupled‐channel theory. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Distribution of Transmission Eigenvalues in Disordered Wires with Symplectic Symmetry

We have numerically studied the electronic transport properties of quantum wires with symplectic symmetry based on the tight-binding model. The asymptotic behavior of the conductance crucially depends on the even–odd effect of the conducting channel, since one perfectly conducting channel exists only in the odd-channel system. The decay length of the conductance and the distribution of the largest transmission eigenvalues clearly show the even–odd difference. Our results are in excellent agreement with the random-matrix theory.

Roles of interactions in electronic properties of quantum disordered wires

AbstractWe studied electronic transport properties of quantum wires with electron–electron interactions and random potentials. We focus in particular on the roles of the interactions in various situations. In a single wire system the interactions would enhance the random potential effect in some cases while they would suppress it in other cases. Taking analytical and numerical approaches, we clarified the roles in Hubbard wire based on the analysis of 4kF impurity scattering. We also studied the influence of inter‐wire interactions between parallel wires in the presence of random potentials and found a rather different role of the interactions on the localization phenomena. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Transport properties of quantum wires

Electron transport in Luttinger liquids connected by tunnel barriers is reviewed. The non-analytic temperature behavior of the conductance of a single tunnel barrier is derived. An overview of charge and spin transport properties through a one-dimensional quantum dot formed by two impurities is given. The temperature and voltage dependences of conductance peaks reveal the non-Fermi liquid correlations. Several spin effects in the linear as well as non-linear transport are predicted. These include a parity effect in linear transport which is due to the Pauli exclusion principle, and negative differential conductances in non-linear transport. The latter are due to charge and spin selection rules and non-Fermi liquid correlations which lead to correlation-induced trapping of higher-spin states. The possibility for experimental verification of this novel effect is discussed.

Spectral and transport properties of quantum wires with bond disorder

Systems with bond disorder are defined through lattice Hamiltonians that are of pure nearest neighbour hopping type, i.e., do not contain on-site contributions. They stand representative for the general family of disordered systems with chiral symmetries. Application of the Dorokhov–Mello–Pereyra–Kumar transfer matrix technique P.W. Brouwer et al. [Phys. Rev. Lett 81 (1998) 862; Phys. Rev. Lett. 84 (2000) 1913] has shown that both spectral and transport properties of quasi one-dimensional systems belonging to this category are highly unusual. Most notably, regimes with absence of exponential Anderson localization are observed, the single particle density of states exhibits singular structure in the vicinity of the band centre, and the manifestation of these phenomena depends in an apparently topological manner on the even- or oddness of the channel number. In this paper we re-consider the problem from the complementary perspective of the nonlinear σ -model. Relying on the standard analogy between one-dimensional statistical field theories and zero-dimensional quantum mechanics, we will relate the problem to the behaviour of a quantum point particle subject to an Aharonov–Bohm flux. We will build on this analogy to re-derive earlier DMPK results, identify a new class of even/odd staggering phenomena (now dependent on the total number of sites in the system) and trace back the anomalous behaviour of the bond disordered system to a simple physical mechanism, viz. the flux periodicity of the quantum Aharonov–Bohm system. We will also touch upon connections to the low energy physics of other lattice systems, notably disordered chiral systems in 0 and 2 dimensions and antiferromagnetic spin chains.

Electron-beam lithography of V-groove quantum wire devices

We have developed electron-beam lithography methods, using multi-layer PMMA resist, in order to fabricate structures with sub-micron features on non-planar substrates. Using these methods, we achieved lift-off of 100 nm wide metallic gates which follow the topography of 1.5 μm deep V-grooves. These devices were used to measure electron transport properties of quantum wires grown in V-grooves. Using such non-planar gate structures, we could observe 1D quantized conduction steps and investigate the phenomena of 2D/1D scattering and quantum contact resistance in these wires.

Nonuniversality in quantum wires with off-diagonal disorder: a geometric point of view

It is shown that, in the scaling regime, transport properties of quantum wires with off-diagonal disorder are described by a family of scaling equations that depend on two parameters: the mean free path and an additional continuous parameter. The existing scaling equation for quantum wires with off-diagonal disorder [Brouwer et al., Phys. Rev. Lett. 81 (1998) 862] is a special point in this family. Both parameters depend on the details of the microscopic model. Since there are two parameters involved, instead of only one, localization in a wire with off-diagonal disorder is not universal. We take a geometric point of view and show that this non-universality follows from the fact that the group of transfer matrices is not semi-simple. Our results are illustrated with numerical simulations for a tight-binding model with random hopping amplitudes.

Electron Transport In One-Dimensional Magnetic Superlattices

Electron transport properties of quantum wires in the presence of a periodically modulated magnetic field are investigated. For a short modulated wire, we find dips in conductance just below each mode threshold. The conductance dips are quite robust at low temperature. Increasing the number of periods of magnetic modulation can lead to the formation of minibands and gaps. The differences between the one dimensional (1D) electric superlattice and 1D magnetic superlattice are discussed. We also consider the spatial distributions of currents, which show dramatic differences between the magnetic superlattices and electric ones.

Quantum interference effects on the electron conduction through negative-potential regions

The quantum interference effects on transport properties of quantum wires including some large obstacles with a negative potential are studied in the presence of a magnetic field. It is found that the magnetoconductance has a quasiperiodic dip structure in the high magnetic field regime. We show that the dips are attributed to an Aharonov-Bohm-type effect and that the period reflects the ring area lying between the inner and outer orbits for the negative-potential region. The effects of the potential edge structure on the conductance are also discussed. The current density around the obstacles and the magnetic field dependence of energy levels are calculated to investigate whole features of the conductance.

Transport properties of quantum wires in spatially periodic magnetic and electrostatic fields

Electron transport properties of quantum wires in the presence of modulated magnetic and electrostatic fields are investigated. We find dips in conductance just below each mode threshold in the presence of a periodic magnetic modulation. The combination of both electrostatic and magnetic modulations makes the conductance dips more pronounced. The effects of temperature and background magnetic field on the conductance dips are also studied. Increasing the number of periods of magnetic modulation can lead to magnetic blocking and reopening of the channel, as the field strength is increased. For higher incoming energy, a larger value of the magnetic modulation amplitude is needed to block the channel and to reopen it. For thicker magnetic barriers, the range of field strength for magnetic reopening narrows. Electrostatic modulation suppresses the magnetic reopening.

Coulomb effects in transport properties of quantum wires.

The Coulomb 1/r interaction plays an important role in quantum wires. We study the interplay between this long-range interaction and impurity. For a single band quantum wire, we find that the transport properties are strongly modified. The linear conductance G is found to vanish with temperature as G\ensuremath{\sim}exp[-\ensuremath{\nu}${\mathrm{ln}}^{3/2}$(1/T)] and the current voltage characteristics acquires a thresholdlike behavior. The possible extension of the theory to the case of many-band quantum wires is discussed.

Role of contacts in mesoscopic devices

The conductance of a mesoscopic device is usually described in terms of the transmission of electrons between electrical contacts. Implicit in this description is the assumption that contacts can be approximated as ideal thermal reservoirs which act solely to thermalise incident electrons before re-injecting them into the device. We describe two classes of experiment where this assumption is not valid. First, when the dissipation in the system is strongly dependent on an external parameter, such as temperature or magnetic field, the physical position of the contact may itself depend the parameter. We study this by investigating the transport properties of quantum wires with disordered contacts. Second, when there is the possibility of some sort of interaction between the electrons in the contact and those in the device, as we find in resonant tunnelling from a 2D contact into a 0D state. In both cases we find that the conductance properties of the device are strongly modified by the nature of the contact. PACS: 73.40.Kp, 73.40.Hm, 73.40Gk

Oscillation of the transport lifetime due to LO phonon scattering in quasi-one-dimensional channels.

The transport properties of quantum wires (QW's), mainly under the action of strong magnetic field, have been studied both theoretically and experimentally. In this report we use the memory-function projection-operator theory to obtain the resistivity of a QW built by structural and electric confinement and show that, in the absence of a magnetic field, oscillations in the transport lifetime appear due to scattering by LO phonons. These oscillations describe the harmonic confinement and are weakly dependent on the carrier concentration in the quantum limit. We suggest that this could be an easy way to characterize that structure using dc transport.