Interacting Quantum Wire Research Articles

Junction of several weakly interacting quantum wires: A renormalization group study

We study the conductance of three or more semi-infinite wires which meet at a junction. The electrons in the wires are taken to interact weakly with each other through a short-range density-density interaction, and they encounter a general scattering matrix at the junction. We derive the renormalization group equations satisfied by the S-matrix, and we identify its fixed points and their stabilities. The conductance between any pair of wires is then studied as a function of physical parameters such as temperature. We discuss the possibility of observing the effects of junctions in present day experiments, such as the four-terminal conductance of a quantum wire and crossed quantum wires.

Electron transport through ballistic quantum channels

We study the 1D transport through open channels of a quantum wire by a Luttinger liquid model. We introduce contact regions lying in between the non-interacting leads and the interacting quantum wire as Luttinger liquids whose properties are governed by the electron parameters in the leads. We place two barriers at the contacts to model imperfect coupling between the leads and the quantum wire. We then show that this model explains several interesting features of recent experiments. We discuss the criteria required to observe resonant transmission through such a quantum wire. We briefly discuss the role of an external magnetic field on transport.

Quantum pump for spin and charge transport in a Luttinger liquid.

We study two different parametric pumps--one for pumping spin currents, the other for charge currents--in interacting quantum wires. We find that, as a function of pumping frequency, the spin or charge pumped per cycle has a nonuniversal crossover--depending on pumping details--between two universal fixed point values of 0 and twice the electronic spin or charge quantum number. The direction of flow between these two fixed points depends on whether the interactions are repulsive or attractive, while the quantization itself is a signature of interactions.

Coulomb correlationsin quantum wires in strong magnetic fields and their contribution tothe Fermi-edge group velocity

The screening of the Coulomb interaction in quantum wires, subjectto strong perpendicular magnetic fields, is assessed by means of anapproximate analytic solution of the integral equation for thescreened potential as well as by the numerical solution of thisequation. The exchange-correlation contribution to the Fermi-edgegroup velocity, vgec(kF), is proved to be nonsingular. Forsufficiently strong magnetic fields, vgec(kF) isapproximately the same as the Hartree velocity vgH(kF). Theenergy dispersion curves, obtained in the screened Hartree-Fockapproximation, agree well with experimental observations.

Static and dynamic image potential for tunneling into a Luttinger liquid

We study electron tunneling from a tip or a lead into an interacting quantum wire described by Luttinger liquid theory. Within a WKB-type approach, the Coulomb interaction between the wire and the tunneling electrons, as well as the finite traversal time are taken into account. Although the static image potential is only logarithmically suppressed against the bare Coulomb interaction, the dynamic image potential is not strong enough to alter power-law exponents entering the tunneling density of states.

Spin transport in interacting quantum wires and carbon nanotubes

We present a general formulation of spin-dependent transport through a clean one-dimensional interacting quantum wire or carbon nanotube, connected to noncollinear ferromagnets via tunnel junctions. The low energy description of each junction is given by a conformally invariant boundary condition representing exchange coupling, in addition to a pair of electron tunneling operators. The effects of the exchange coupling are strongly enhanced by interactions, leading to a dramatic suppression of spin accumulation: a direct signature of spin-charge separation. Finally, backscattering induces nonequilibrium oscillations in the current-voltage relation.

Single-particle excitations and many-particle interactions in quantum wires and dots.

We have investigated electronic excitations in GaAs-AlxGa1-xAs quantum wires, and dots by resonance Raman spectroscopy. We find for quantum dots and quantum wires three types of excitations; single-particle, spin-density, and charge-density excitations (SPE's, SDE's, and CDE's, respectively). Our experiments show that SPE's are enhanced under conditions of extreme resonance, which indicates that energy-density fluctuations are responsible for the excitation of unscreened SPE's. The high intensity of the SPE's allows a detailed analysis of collective effects in the zero- and one-dimensional electron systems.

Conductance increase by electron-phonon interaction in quantum wires.

We investigate the influence of electron-phonon interactions on the DC-conductance $\Gamma $ of a quantum wire in the limit of one occupied subband. At zero temperature, a Tomonaga-Luttinger-like renormalization of $\Gamma $ to a value slightly larger than $2e^{2}/h$ is calculated for a realistic quantum wire model.

Phonoconductivity measurements of the electron-phonon interaction in quantum wire structures

Abstract We have used a phonoconductivity technique to investigate the electron-phonon interaction in quantum wires. This interaction has important consequences for certain aspects of device behaviour. The 10 μm long wires were formed in GaAs/AlGaAs heterojunctions using split-gates. Ballistic phonon pulses, with an approximately Planckian frequency spectrum, were generated by a resistive film heater on the opposite side of the substrate. The interaction of the phonons with the quantum wire was detected via changes in conductance of the device. Oscillations in the phonoconductivity were observed with increasing (negative) gate bias. These oscillations were related to the Fermi level position relative to the one-dimensional subband structure which was determined from electrical transport measurements. We give a qualitative explanation of the results in terms of phonon induced inter- and intra- 1D subband electronic transitions leading to changes in the electron temperature which in turn affect the conductance. From our results we obtain a value for the effective width of the quantum wire.

Exciton confinement effects in nonlinear optical spectroscopy of interacting quantum wires

Nonlinear light scattering and four-wave mixing from N interacting quantum wires are calculated using Green function techniques. Size confinement results in discrete single- and two-photon resonances. The nonlinear signal per wire increases with N for small N, and saturates at large N. Effects of interactions within wires and among wires on the nonlinear signal and the coherence size are analyzed. The shapes of single-photon resonances for small N (quasi 1D) and for large N (quasi 2D) are compared.

Polar-optical oscillations and electron-phonon interaction in quantum wires and quantum dots

A theory for long-wavelength optical phonons in quantum wires and quantum dots is developed under very general conditions. Confined and interface modes are obtained as solutions of the full system of four coupled second-order differential equations for the vibrational amplitudes and the electrostatic potential. These equations are solved without incompatibility between the mechanical and electrostatic matching boundary conditions. The eigensolutions and eigenmodes for cylindrical quantum wires and spherical quantum dots are found in terms of the longitudinal and transverse parts of the mechanical vibrational field and the electrostatic field, all appropriately coupled. The pure surface phonons (Fröhlich phonons) are obtained as a particular case. The orthogonality and the general conditions under which the set of eigensolutions form a complete basis are established. The electron-phonon interaction Hamiltonians are given in explicit form.

Optical phonons and electron-phonon interaction in quantum wires.

A unified macroscopic continuum theory for the treatment of optical-phonon modes in quantum-wire structures is established. The theory is based on a Lagrangian formalism from which the equations of motion are rigorously derived. They consist of four coupled second-order differential equations for the vibrational amplitude and electrostatic potential. The matching boundary conditions are obtained from the fundamental equations. It is shown that no incompatibility exists between mechanical and electrostatic matching boundary conditions when a correct mathematical treatment of the problem is given. The particular case of a GaAs quantum wire buried in AlAs, where the phonons can be considered completely confined, is analyzed and the vector displacement and electron-phonon interaction potential are illustrated for several modes.