50 research outputs found
Electron tunneling into a quantum wire in the Fabry-Perot regime
No full textWe study a gated quantum wire contacted to source and drain electrodes in the Fabry-Pérot regime. The wire is also coupled to a third terminal (tip), and we allow for an asymmetry of the tip tunneling amplitudes of right-moving and left-moving electrons. We analyze configurations where the tip acts as an electron injector or as a voltage probe and show that the transport properties of this three-terminal setup exhibit very rich physical behavior. For a noninteracting wire we find that a tip in the voltage-probe configuration affects the source-drain transport in different ways, namely, by suppressing the conductance, by modulating the Fabry-Pérot oscillations, and by reducing their visibility. The combined effect of electron-electron interaction and finite length of the wire, accounted for by the inhomogeneous Luttinger liquid model, leads to significantly modified predictions as compared to models based on infinite wires. We show that when the tip injects electrons asymmetrically the charge fractionalization induced by interaction cannot be inferred from the asymmetry of the currents flowing in source and drain. Nevertheless interaction effects are visible as oscillations in the nonlinear tip-source and tip-drain conductances. Important differences with respect to a two-terminal setup emerge, suggesting new strategies for the experimental investigation of Luttinger liquid behavio
Rashba effect in quantum networks
No full textWe present a formalism to study quantum networks made up by single-channel quantum wires in the presence of Rashba spin-orbit coupling and magnetic field. In particular, linear transport through one-dimensional and two-dimensional finite-size networks is studied by means of the scattering formalism. In some particular quantum networks, the action of the magnetic field or of the Rashba spin-orbit coupling induces localization of the electron wave function. This phenomenon, which relies on both the quantum-mechanical interference and the geometry of the network, is manifested through the suppression of the conductance for specific values of the spin-orbit-coupling strength or of the magnetic field. Furthermore, the interplay of the Aharonov-Bohm phases and of the non-Abelian phases introduced by spin-orbit coupling, is discussed in a number of cases
Rashba-effect-induced localization in quantum networks
No full textWe study a quantum network extending in one dimension (chain of square loops connected at one vertex) made up of quantum wires with Rashba spin-orbit coupling. We show that the Rashba effect may give rise to an electron localization phenomenon similar to the one induced by magnetic field. This localization effect can be attributed to the spin precession due to the Rashba effect. We present results both for the spectral properties of the infinite chain and for linear transport through a finite-size chain connected to leads. Furthermore, we study the effect of disorder on the transport properties of this network
Quantum networks in the presence of the Rashba effect and a magnetic field
No full textWe use a simple formalism to calculate the conductance of any quantum network consisting of single- channel one-dimensional quantum wires in the presence of Rashba spin-orbit coupling and a coupling magnetic field. We show that the Rashba effect may give rise to an electron localization phenomenon similar to the Aharonov-Bohm effect. This localization effect can be attributed to spin precession due to the Rashba effect. We present results for linear transport through a finite-size chain connected to leads, taking also the effect of disorder into account. The effects of applying a magnetic field and Rashba spinorbit coupling are studied in two-dimensional networks, showing that their interplay can lead the system to a transition between localized and anti-localized behaviour
Rashba quantum wire: exact solution and ballistic transport
No full textThe effect of Rashba spin-orbit interaction in quantum wires with hard-wall boundaries is discussed. The exact wavefunction and eigenvalue equation are worked out, pointing out the mixing between the spin and spatial parts. The spectral properties are also studied within perturbation theory with respect to the strength of the spin-orbit interaction and diagonalization procedure. A comparison is made with the results of a simple model, the two-band model, that takes account only of the first two sub-bands of the wire. Finally, the transport properties within the ballistic regime are analytically calculated for the two-band model and through a tight-binding Green function for the entire system. Single and double interfaces separating regions with different strengths of spin-orbit interaction are analysed by injecting carriers into the first and the second sub-band. It is shown that in the case of a single interface the spin polarization in the Rashba region is different from zero, and in the case of two interfaces the spin polarization shows oscillations due to spin-selective bound states
Spin polarization of electrons with Rashba double-refraction
No full textWe demonstrate how the Rashba spin�orbit coupling in semiconductor heterostructures can produce and control a spin-polarized current without ferromagnetic leads. The key idea is to use spin-double refraction of an electronic beam with a nonzero incidence angle. A region where the spin�orbit coupling is present separates the source and the drain without spin�orbit coupling. We show how the transmission and the beam spin polarization critically depend on the incidence angle. The transmission halves when the incidence angle is greater than a limit angle and a significant spin polarization appears. On increasing the spin�orbit coupling one can obtain the modulation of the intensity and of the spin polarization of the output electronic current when the input current is unpolarized. Our analysis shows the possibility of realizing a spin-field-effect transistor based on the propagation of only one mode with the region with spin�orbit coupling, whereas the original Datta and Das device (1990 Appl. Phys. Lett. 56 665) uses the spin precession that originates from the interference between two modes with orthogonal spin
Spin-dependent transport in nanostructures
No full textThe Dissertation takes account of the effect of the spin-orbit
coupling interactions in the properties of mesoscopic systems. The
Manuscript is divided in three main part. In the first part (Chapter
1) the spin-orbit interaction in mescoscopic system is introduced. In
the second part (Chapter 2 and 3) the spin-double refraction is
introduced. Furthermore, it is shown how to realize a
spin-field-effect transistor based on it. In the last part (Chapter
4), the effect of spin-orbit interaction in quantum network is studied
Ground state features of the Fröhlich model
No full textFollowing the ideas behind the Feynman approach, a variational wave function is proposed for the Fröhlich model. It is shown that it provides, for any value of the electron-phonon coupling constant, an estimate of the polaron ground state energy better than the Feynman method based on path integrals. The mean number of phonons, the average electronic kinetic and interaction energies, the ground state spectral weight and the electron-lattice correlation function are calculated and successfully compared with the best available results. Copyright Springer-Verlag Berlin/Heidelberg 2003
Transport Properties of an Electron-Hole Bilayer in Contact with a Superconductor Hybrid Junction
No full textWe investigate the transport properties of a junction consisting of an electron-hole bilayer in contact with normal and superconducting leads. The electron-hole bilayer is considered as a semimetal with two electronic bands. We assume that in the region between the contacts the system hosts an exciton condensate described by a BCS-like model with a gap Γ in the quasiparticle density of states. We first discuss how the subgap electronic transport through the junction is mainly governed by the interplay between two kinds of reflection processes at the interfaces: the standard Andreev reflection at the interface between the superconductor and the exciton condensate, and a coherent crossed reflection at the semimetal-exciton-condensate interface that converts electrons from one layer into the other. We show that the differential conductance of the junction shows a minimum at voltages of the order of Γ/e. Such a minimum can be seen as a direct hallmark of the existence of the gapped excitonic state.QN/Klapwijk La
Spin-resolved scattering through spin-orbit nanostructures in graphene
No full textWe address the problem of spin-resolved scattering through spin-orbit nanostructures in graphene, i.e., regions of inhomogeneous spin-orbit coupling on the nanometer scale. We discuss the phenomenon of spin-double refraction and its consequences on the spin polarization. Specifically, we study the transmission properties of a single and a double interface between a normal region and a region with finite spin-orbit coupling, and analyze the polarization properties of these systems. Moreover, for the case of a single interface, we determine the spectrum of edge states localized at the boundary between the two regions and study their properties
