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Giovanni Vignale

Publications and source records attributed to Giovanni Vignale.

120 records · Page 7Linked to original sources
arXiv1999

Effect of disorder on the non-dissipative drag

In this paper we consider the effect of disorder on the non-dissipative Coulomb drag between two mesoscopic metal rings at zero temperature. Ring 1 has an Aharonov-Bohm flux present which creates a persistent current J_0. Ring 2 interacts with ring 1 via the Coulomb potential and a drag current, J_d is produced. We show that this drag current persists with finite disorder in each ring, and that for small disorder, J_d decreases with the square of the disorder amplitude.

cond-mat.mes-hall↗
arXiv1999

Continuum elasticity theory of edge excitations in a two-dimensional electron liquid with finite range interactions

We make use of continuum elasticity theory to investigate the collective modes that propagate along the edge of a two-dimensional electron liquid or crystal in a magnetic field. An exact solution of the equations of motion is obtained with the following simplifying assumptions: (i) The system is {\it macroscopically} homogeneous and isotropic in the half-plane delimited by the edge (ii) The electron-electron interaction is of finite range due to screening by external electrodes (iii) The system is nearly incompressible. At sufficiently small wave vector $q$ we find a universal dispersion curve $ω\sim q$ independent of the shear modulus. At larger wave vectors the dispersion can change its form in a manner dependent on the comparison of various length scales. We obtain analytical formulas for the dispersion and damping of the modes in various physical regimes.

cond-mat.mes-hall↗
arXiv1998

Exact exchange-correlation potential for a time-dependent two electron system

We obtain an exact solution of the time-dependent Schroedinger equation for a two-electron system confined to a plane by an isotropic parabolic potential whose curvature is periodically modulated in time. From this solution we compute the exact time-dependent exchange correlation potential v_xc which enters the Kohn-Sham equation of time-dependent density functional theory. Our exact result provides a benchmark against which various approximate forms for v_xc can be compared. Finally v_xc is separated in an adiabatic and a pure dynamical part and it is shown that, for the particular system studied, the dynamical part is negligible.

cond-mat↗
arXiv1997

Engineering Superfluidity in Electron-Hole Double Layers

We show that band-structure effects are likely to prevent superfluidity in semiconductor electron-hole double-layer systems. We suggest the possibility that superfluidity could be realized by the application of uniaxial pressure perpendicular to the electron and hole layers.

cond-mat↗
arXiv1996

Collective Modes and Electronic Spectral Function in Smooth Edges of Quantum Hall Systems

We present a microscopic theory of the collective modes of a ``smooth'' edge of a quantum Hall system, showing under what conditions these modes can be described as a set of independent bosons. We then calculate the electronic spectral function in an independent-boson model - a procedure that reduces to standard bosonization in the limit of ``sharp'' edge. The I-V tunneling characteristics deduced from this model exhibit, for low voltage, a power law behavior, with exponents that differ significantly from those of the sharp edge model.

cond-mat↗
arXiv1995

Drag in paired electron-hole layers

We investigate transresistance effects in electron-hole double layer systems with an excitonic condensate. Our theory is based on the use of a minimum dissipation premise to fix the current carried by the condensate. We find that the drag resistance jumps discontinuously at the condensation temperature and diverges as the temperature approaches zero.

cond-mat↗
arXiv1995

Equilibrium Current and Orbital Magnetization in a Quantum Hall Fluid

We present a general theory for the equilibrium current distribution in an interacting two-dimensional electron gas subjected to a perpendicular magnetic field, and confined by a potential that varies slowly on the scale of the magnetic length. The distribution is found to consist of strips or channels of current, which alternate in direction, and which have universal integrated strength.

cond-mat↗
arXiv1994

Universal Equilibrium Currents in the Quantum Hall Fluid

The equilibrium current distribution in a quantum Hall fluid that is subjected to a slowly varying confining potential is shown to generally consist of strips or channels of current, which alternate in direction, and which have universal integrated strengths. A measurement of these currents would yield direct independent measurements of the proper quasiparticle and quasihole energies in the fractional quantum Hall states.

cond-mat↗
arXiv1994

Currents in the Compressible and Incompressible Regions of the 2DEG

We derive a general expression for the low-temperature current distribution in a two-dimensional electron gas, subjected to a perpendicular magnetic field and in a confining potential that varies slowly on the scale of the magnetic length l. The analysis is based on a self-consistent one-electron description, such as the Hartree or standard Kohn-Sham equations. Our expression, which correctly describes the current distribution on scales larger than l, has two components: One is an ``edge current'' which is proportional to the local density gradient and the other is a ``bulk current'' which is proportional to the gradient of the confining potential. The direction of these currents generally displays a striking alternating pattern.

cond-mat↗
arXiv1994

Rigorous upper bound for the persistent current in systems with toroidal geometry

It is shown that the absolute value of the persistent current in a system with toroidal geometry is rigorously less than or equal to $e \hbar N /4 πm r_0^2$, where $N$ is the number of electrons, and $r_0^{-2} = \langle r_i^{-2}\rangle$ is the equilibrium average of the inverse of the square of the distance of an electron from an axis threading the torus. This result is valid in three and two dimensions for arbitrary interactions, impurity potentials, and magnetic fields.

cond-mat↗
arXiv1994

Bound on the Group Velocity of an Electron in a 1D Periodic Potential

By using a recently derived upper bound on the allowed equilibrium current in a ring, it is proved that the magnitude of the group velocity of a Bloch electron in a one-dimensional periodic potential is always less than or equal to the group velocity of the same Bloch state in an empty lattice. Our inequality also implies that each energy band in a one-dimensional crystal always lies below the corresponding free-electron band, when the minima of those bands are aligned.

cond-mat↗