Vassilios Vargiamidis

Shape effects on scattering in three-dimensional quantum wires

We study the effects of the shape of the cross section of a three-dimensional quantum wire on electron scattering from a single point defect in the wire. The confinement of electrons is modeled by both hard- and soft-wall potentials. We find that as the degree of anisotropy of the cross section of the wire is increased intersubband electron scattering is enhanced and intrasubband transmission is suppressed making it appear as though the defect has stronger impact on electron scattering for asymmetric cross sections. Also, increasing the anisotropy of the cross section results in a decrease of the values of the conductance. Furthermore, for the soft-wall confinement the conductance as a function of Fermi energy rises faster than the conductance for the hard-wall confinement. We use the Lippmann–Schwinger equation of scattering theory in order to calculate analytically the transmission coefficients.

Electric-field effects on Fano resonances and transmission phase through quantum wires

The effect of a transverse electric field on Fano line shapes in electronic transport through a quantum wire is investigated via a Feshbach three-channel model. The coupling between channels is provided by an attractive short-range scatterer with lateral extent. It is shown that the resonance structure in a particular subband is sensitive on the electric field strength and direction. In particular, collapse of a Fano profile either in the first or the second subband may occur, depending on whether the electric field points in the negative or positive direction, respectively. This is due to the vanishing coupling between the bound states and the conduction ones which, in turn, is a consequence of the electric field-induced shift of the confining potential. This tunability of Fano resonances may prove experimentally useful in ballistic transport through narrow channels. The results in the first subband are compared with those obtained from a two-channel model. A detailed account of the transmission phase is...

Temperature dependence of scattering phases and Friedel phase discontinuity in quantum wires

Two important issues concerning the scattering phases in a quantum wire with an attractive scatterer are investigated. We consider the case of two quasibound states which couple to a scattering channel and give rise to two Fano resonances. First, we examine the effects of temperature on the phase of the transmission amplitude and the Friedel phase. It is shown that temperature effects tend to smear sharp features of the transmission phase; namely, the phase drops become less than π, and acquire finite widths which increase linearly in the low-temperature regime. The influence of temperature on the Friedel phase and density of states becomes stronger as the Fano resonance becomes narrower. Second, we examine the behavior of the Friedel phase when the energy of the incident electron crosses an infinitely narrow Fano resonance, forming bound state in the continuum. It is shown that the Friedel phase exhibits abrupt jump of π at this energy. We discuss this odd behavior in relation to the Friedel sum rule and...

Effects of Temperature on the Scattering Phases and Density of States in Quantum Wires

We investigate the effects of temperature on the scattering phases in a quantum wire with an attractive scatterer. We consider two bound states, belonging to different subbands, which couple to a scattering channel and give rise to two Fano resonances. In this context, we first demonstrate the deviation of the transmission phase from the Friedel phase at the zeros of the transmission. It is then shown that temperature effects tend to smear sharp features of the transmission phase; namely, the phase drops become less than π and acquire finite widths, which increase linearly in the low-temperature regime. The influence of temperature on the Friedel phase and density of states is also examined.

Friedel Sum Rule in One- and Quasi-One-Dimensional Wires

We consider the Friedel sum rule (FSR) in the context of scattering in one- and quasi-one-dimensional ballistic wires with a double δ potential. In particular, we analyze the relation between the density of states (DOS) obtained from the energy derivative of the Friedel phase (or the scattering matrix) and that obtained from the Green’s function. We show that the local FSR is valid when a correction term is included. Various properties of the one-dimensional local DOS are also discussed.