Conductance Of Quantum Wire Research Articles

Density-matrix renormalization group study of the linear conductance in quantum wires coupled to interacting leads or phonons

In a previous paper [J.-M. Bischoff and E. Jeckelmann, Phys. Rev. B 96, 195111 (2017)] we introduced a density-matrix renormalization group method for calculating the linear conductance of one-dimensional correlated quantum systems and demonstrated it on homogeneous spinless fermion chains with impurities. Here we present extensions of this method to inhomogeneous systems, models with phonons, and the spin conductance of electronic models. The method is applied to a spinless fermion wire-lead model, the homogeneous spinless Holstein model, and the Hubbard model. Its capabilities are demonstrated by comparison with the predictions of Luttinger liquid theory combined with Bethe Ansatz solutions and other numerical methods. We find a complex behavior for quantum wires coupled to interacting leads when the sign of the interaction (repulsive/attractive) differs in wire and leads. The renormalization of the conductance given by the Luttinger parameter in purely fermionic systems is shown to remain valid in the Luttinger liquid phase of the Holstein model with phononic degrees of freedom.

Spin-orbit coupling and resonances in the conductance of quantum wires

We investigate a possibility of pair electron-electron ($e\ensuremath{-}e$) collisions in a ballistic wire with spin-orbit coupling and only one populated mode. Unlike in a spin-degenerate system, a combination of spin splitting in momentum space with a momentum-dependent spin precession opens up a finite phase space for pair $e\ensuremath{-}e$ collisions around three distinct positions of the wire's chemical potential. For a short wire, we calculate the corresponding resonant contributions to the conductance, which have different power-law temperature dependencies, and, in some cases, vanish if the wire's transverse confinement potential is symmetric. Our results may explain the recently observed feature at the lower conductance plateau in InAs wires.

EFFECT OF ASYMMETRIC QUANTUM DOT RINGS IN ELECTRON TRANSPORT THROUGH A QUANTUM WIRE

The electronic conductance at zero temperature through a quantum wire with side-connected asymmetric quantum ring (as a scatter system) is theoretically studied using the non-interacting Hamiltonian Anderson tunneling method. In this paper we concentrate on the configuration of the quantum dot rings. We show that the asymmetric structure of QD-scatter system strongly influences the amplitude and spectrum of electron transport characteristics through a quantum wire. We find that the unbalanced number of quantum dots in two rings rather increases the anti-resonant in quantum wire conductance than balances the number of quantum dots rings. Also changing the distance between quantum dot rings influences the amplitude of resonant peaks in the QW conductance spectrum. The proposed asymmetric quantum ring scatter system idea in this paper opens a new insight on the designing of nano structure quantum wire for a given electrical conductance.

Scattering of charge and spin excitations and equilibration of a one-dimensional Wigner crystal

We study scattering of charge and spin excitations in a system of interacting electrons in one dimension. At low densities, electrons form a one-dimensional Wigner crystal. To a first approximation, the charge excitations are the phonons in the Wigner crystal, and the spin excitations are described by the Heisenberg model with nearest-neighbor exchange coupling. This model is integrable and thus incapable of describing some important phenomena, such as scattering of excitations off each other and the resulting equilibration of the system. We obtain the leading corrections to this model, including charge-spin coupling and the next-nearest-neighbor exchange in the spin subsystem. We apply the results to the problem of equilibration of the one-dimensional Wigner crystal and find that the leading contribution to the equilibration rate arises from scattering of spin excitations off each other. We discuss the implications of our results for the conductance of quantum wires at low electron densities.

Conductance in quantum wires by three quantum dots arrays

A noninteracting quantum-dot arrays side coupled to a quantum wire is studied. Transport through the quantum wire is investigated by using a noninteracting Anderson tunneling Hamiltonian. The conductance at zero temperature develops an oscillating band with resonances and antiresonances due to constructive and destructive interference in the ballistic channel, respectively. Moreover, we have found the number of antiresonant exactly depends on the number of quantum dot in every array and increasing array make antiresonants wide increase.

Correlating Electronic Transport to Atomic Structures in Self-Assembled Quantum Wires

Quantum wires, as a smallest electronic conductor, are expected to be a fundamental component in all quantum architectures. The electronic conductance in quantum wires, however, is often dictated by structural instabilities and electron localization at the atomic scale. Here we report on the evolutions of electronic transport as a function of temperature and interwire coupling as the quantum wires of GdSi(2) are self-assembled on Si(100) wire-by-wire. The correlation between structure, electronic properties, and electronic transport are examined by combining nanotransport measurements, scanning tunneling microscopy, and density functional theory calculations. A metal-insulator transition is revealed in isolated nanowires, while a robust metallic state is obtained in wire bundles at low temperature. The atomic defects lead to electron localizations in isolated nanowire, and interwire coupling stabilizes the structure and promotes the metallic states in wire bundles. This illustrates how the conductance nature of a one-dimensional system can be dramatically modified by the environmental change on the atomic scale.

3Pa1-1 Temperature dependence of thermal conductivity in quantum wires due to interaction between two-level systems and phonons(Poster Session)

3Pa1-1 Temperature dependence of thermal conductivity in quantum wires due to interaction between two-level systems and phonons(Poster Session)

Non-equilibrium transport in a quantum wire in the quantum Hall regime

We investigate the equilibrium and non-equilibrium electron transport in a quantum wire (QW) in the quantum Hall regime. While the equilibrium conductance of the QW is quantized reflecting the dissipation-less quantum Hall edge transport, the quantization collapses when the QW is voltage-biased with the voltages larger than the critical ones. This phenomenon is accompanied by the dynamic nuclear polarization which causes the temporal variation of the QW conductance of the order of minutes.

Equilibration of Luttinger Liquid and Conductance of Quantum Wires

Luttinger liquid theory describes one-dimensional electron systems in terms of noninteracting bosonic excitations. In this approximation thermal excitations are decoupled from the current flowing through a quantum wire, and the conductance is quantized. We show that relaxation processes not captured by the Luttinger liquid theory lead to equilibration of the excitations with the current and give rise to a temperature-dependent correction to the conductance. In long wires, the magnitude of the correction is expressed in terms of the velocities of bosonic excitations. In shorter wires it is controlled by the relaxation rate.

Spin-orbit coupling and the electronic properties of quantum wires

We review recent work on the effects of the Rashba spin-orbit interaction on the electronic structure and the conductance of quantum wires. We first discuss the importance of the intersubband coupling induced by the Rashba interaction for the wire subband-energies and spin distributions, especially in the presence of in-plane magnetic fields. We then consider the calculation of the evanescent modes, emphasizing the peculiarities of these states in the presence of spin-orbit coupling. Finally, we discuss the physical effects of a localized Rashba interaction in a quantum wire. We predict in this case the occurrence of Fano resonances in the dependence of the wire conductance with the incident electron energy. The Fano lineshapes manifest themselves more clearly in the spin-resolved transmissions. We obtain exact numerical results within the quantum-transmittingboundary algorithm and also propose a simplified approach (the coupled-channel model) that captures the main ingredients of the effect and allows a more transparent physical interpretation.

Thermal conductance in quantum wire with two obstacles

Based on the scattering-matrix method, the influence of obstacles on the thermal conductance in quantum wire was investigated. Three types of obstacles are employed in our calculation. We present a detailed study of the thermal conductance as a function of distance between two obstacles and temperature. The results show that there is qualitative difference in the dependence of the thermal conductance versus width between two obstacles for different temperatures. We also find that the calculated thermal conductance increases with the width W of quantum wire in all cases.

The influence of boundary conditions on thermal conductance in semiconductor quantum wire with structural defect

Using the scattering-matrix method, we investigate the influences of boundary conditions on thermal conductance in quantum wire with structural defect. A comparison between the thermal conductances is made when stress-free, hard-wall, and mixed boundary conditions are applied for acoustic transport leads. The results show that the quantized thermal conductance plateau at very low temperature can be observed only in transport lead with stress-free boundary condition. For hard-wall or mixed boundary conditions, qualitatively different thermal conductance characteristics are found. Moreover, we find that the behavior of the thermal conductance sensitively depend on the geometric parameters and the position of the defect in quantum wire.

Conductance of quantum wires: A numerical study of effects of an impurity and interactions

We use the non-equilibrium Green's function formalism along with a self-consistent Hartree-Fock approximation to numerically study the effects of a single impurity and interactions between the electrons (with and without spin) on the conductance of a quantum wire. We study how the conductance varies with the wire length, the temperature, and the strength of the impurity and interactions. The dependence of the conductance on the wire length and temperature is found to be in rough agreement with the results obtained from a renormalization group analysis based on the Hartree-Fock approximation. For the spin-1/2 model with a repulsive on-site interaction or the spinless model with an attractive nearest neighbor interaction, we find that the conductance increases with increasing wire length or decreasing temperature. This can be qualitatively explained using the Born approximation in scattering theory. For a strong impurity, the conductance is significantly different for a repulsive and an attractive impurity; this is due to the existence of a bound state in the latter case. In general, the large density deviations at short distances have an appreciable effect on the conductance which is not captured by the renormalization group analysis.

Ground state structure and conductivity of quantum wires of infinite length and finite width

We have studied the ground state structure of quantum strips within the local spin-density approximation, for a range of electronic densities between $\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{4}$ and $2\ifmmode\times\else\texttimes\fi{}{10}^{6}{\mathrm{cm}}^{\ensuremath{-}1}$ and several strengths of the lateral confining potential. The results have been used to address the conductance $G$ of quantum strips. At low density, when only one subband is occupied, the system is fully polarized and $G$ takes a value close to $0.7(2{e}^{2}∕h)$, decreasing with increasing electron density in agreement with experiments. At higher densities the system becomes paramagnetic and $G$ takes a value near $(2{e}^{2}∕h)$, showing a similar decreasing behavior with increasing electron density. In both cases, the physical parameter that determines the value of the conductance is the ratio $K∕{K}_{0}$ of the compressibility of the system to the free one.

Transverse magneto‐conductivity of diluted magnetic semicon‐ductor quantum wires

We calculated the transverse dc electrical conductivity of a quasi-one-dimensional semiconductor quantum wire in a magnetic field normal to the barriers of the wire, and studied the electron-magnon interaction in DMS using linear response theory. The electron gas was assumed as quasi-one-dimensional, while the magnons were considered to be bulk type. The transverse dc electrical conductivity of quantum wires of diameter W (∼0.1 µm) much larger than the magnetic length lband much smaller than the mean free path le (e.g., lb ≪ W ≪le), was modelled with a parabolic potential of frequency Ω, and leads to a shift of the magneto-magnon resonance peaks to smaller magnetic fields. Moreover, the magneto-conductivity σxx decreases when the confinement becomes stronger (when the wire diameter decreases). Numerical results are presented for a Ga1–xMnxAs quasi-one-dimensional wire, where we present the appropriate conditions for use of these structures in spintronic applications and devices. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Polarization of nuclear spins from the conductance of quantum wire.

We devise an approach to measure the polarization of nuclear spins via conductance measurements. Specifically, we study the combined effect of external magnetic field, nuclear spin polarization, and Rashba spin-orbit interaction on the conductance of a quantum wire. Nonequilibrium nuclear spin polarization affects the electron energy spectrum making it time dependent. Changes in the extremal points of the spectrum result in time dependence of the conductance. The conductance oscillation pattern can be used to obtain information about the amplitude of the nuclear spin polarization and extract the characteristic time scales of the nuclear spin subsystem.

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 T<<J this effect is small, and the conductance of the wire remains close to 2e2/h. At T>>J the spin effect reduces the conductance to e2/h.

Complex behavior of the conductance of quantum wires with a long quantum-dot array

We consider electron transport through a quantum wire with an attached quantum-dot array, when the number of dots is large. To this end, we use a noninteracting Anderson Hamiltonian. The conductance at zero temperature shows a complex behavior as a function of the Fermi energy. In particular, two well-defined energy regions are observed. Far from the site-energy of the quantum dots, the conductance depends smoothly on the Fermi energy. On the contrary, at the center of the band the conductance develops an oscillating pattern with resonances and antiresonances due to constructive and destructive interference in the ballistic channel, respectively. We discuss analytically in detail the physical origin of this complex behavior.

Rational sequences for the conductance in quantum wires from affine Toda field theories

We analyse the expression for the conductance of a quantum wire which is decribed by an integrable quantum field theory. In the high temperature regime we derive a simple formula for the filling fraction. This expression involves only the inverse of a matrix which contains the information of the asymptotic phases of the scattering matrix and the solutions of the constant thermodynamic Bethe ansatz equations. Evaluating these expressions for minimal affine Toda field theory we recover several sequences of rational numbers, which are multiples of the famous Jain sequence for the filling fraction occurring in the context of the fractional quantum Hall effect. For instance we obtain $\nu= 4 m/(2m +1)$ for $A_{4m-1}$-minimal affine Toda field theory. The matrices involved have in general non-rational entries and are not part of previous classification schemes based on integral lattices.

Conductance renormalization and conductivity in quantum wires with multiple subbands

Using a Tomonaga–Luttinger model, we studied the conductance renormalization and conductivity of a quantum wire with multiple subbands. As in a single-band system, the conductance of a quantum wire with an arbitrary number of subbands is not renormalized by the electron–electron interaction. For a dirty Tomonaga–Luttinger model with multiple subbands, we found that inter-subband interaction enhances the conductivity, which is contrary to that expected from the intra-subband repulsive interaction, and that the conductivity increases with increasing number of subbands.