arXiv subjects

Roberto Iengo

Publications and source records attributed to Roberto Iengo.

44 records · Page 3Linked to original sources

arXiv1996

Edge Tunneling of Vortices in Superconducting Thin Films

We investigate the phenomenon of the decay of a supercurrent due to the zero-temperature quantum tunneling of vortices from the edge in a thin superconducting film in the absence of an external magnetic field. An explicit formula is derived for the tunneling rate of vortices, which are subject to the Magnus force induced by the supercurrent, through the Coulomb-like potential barrier binding them to the film's edge. Our approach ensues from the non-relativistic version of a Schwinger-type calculation for the decay of the 2D vacuum previously employed for describing vortex-antivortex pair-nucleation in the bulk of the sample. In the dissipation-dominated limit, our explicit edge-tunneling formula yields numerical estimates which are compared with those obtained for bulk-nucleation to show that both mechanisms are possible for the decay of a supercurrent.

cond-mat↗

arXiv1996

Microscopic Oscillations in the Quantum Nucleation of Vortices Subject to Periodic Pinning Potential in a Thin Superconductor

We present a theory for the decay of a supercurrent through nucleation of vortex-antivortex pairs in a two-dimensional superconductor in the presence of dissipation and of a periodic pinning potential. Through a powerful quantum electrodynamics formulation of the problem we show that the nucleation rate develops oscillations in its current-density dependence which are connected to the pinning periodicity. A remnant of the dissipation-driven localization transition is present, and an estimate of the nucleation rate suggests that these effects might be observable in real thin superconductors.

cond-mat↗

arXiv1995

Vortex Pair Production and Decay of a 2-D Supercurrent by a Quantum Field Theory Approach

We investigate the phenomenon of the decay of a supercurrent through homogeneous nucleation of vortex-antivortex pairs in a 2-D like superconductor or superfluid by means of a quantum electrodynamics formulation for the decay of the 2-D vacuum. The case in which both externally-driven current and Magnus force are present is treated exactly, taking the vortex activation energy and its inertial mass as independent parameters. Quantum dissipation is included through the Caldeira and Leggett formulation. Its most relevant consequence is the elimination of the threshold for vortex production due to the Magnus force. In the dissipation-dominated case, formally the limit of zero inertial mass, an exact formula for the pair production rate is given. If however the inertial mass is strictly zero we find that vortex production is inhibited by a quantum effect related to the Magnus force. The possibility of vortex pinning is investigated by means of an effective harmonic potential. While an additional term in the activation energy can account for the effect of a finite barrier in the direction perpendicular to the current, pinning along the current depresses the role of the Magnus force in the dissipation-dominated dynamics, except for the above-mentioned quantum effect. A possible description of vortex nucleation due to the combined effects of temperature and externally-driven currents is also presented along with an evaluation of the resulting voltage drop.

cond-mat↗

arXiv1994

Persistent supercurrents in a planar non-relativistic chiral fluid

We study the possible stationary persistent supercurrents flowing on a cylindrical sample supporting a two-dimensional charged fluid. The internal dynamics of the fluid is obtained by means of an effective theory in which the fluid self-interacts through a $U(1)$ gauge field. We find that the presence of persistent supercurrents depends on what kind of gauge field it is. In particular the current is zero if it is a Maxwell gauge field, and it is maximal if it is a Chern-Simons gauge field. There is an intermediate behaviour in presence of both Maxwell and Chern-Simons term. Therefore it appears that persistent supercurrents are possible only if the fluid is chiral.

hep-th↗

arXiv1994

Magnetic screening properties of an incompressible chiral fluid

We study the possible penetration of a static magnetic field in an idealized sample of many layers supporting a two dimensional charged chiral quantum fluid, to see whether there is a kind of Meissner effect. This is a non standard problem since the quantum fluid is incompressible having a gap in its spectrum. We find that the system shows an intermediate behaviour between superconducting and non-superconducting fluids, the magnetic field being screened or not depending on its orientation relative to the layers.

cond-mat↗

arXiv1993

Comment On Vortices In Chern-Simons And Maxwell Electrodynamics

We compare the vortex-like solutions of two different theories in (2+1) dimensions. In the first a nonrelativistic field self-interacts through a Chern-Simons gauge connection. It is $P$ and $T$ violating. The second is the standard Maxwell scalar electrodynamics. We show that for specific values of some parameters the same vortex-configurations provide solutions for both theories.

hep-th↗

arXiv1993

Effective Theory of a Chiral Superfluid

We consider an effective Lagrangian describing a fluid living on two-di\-men\-sio\-nal planes. The fluid self-interacts through a Chern-Simons vector potential, whose field strength is proportional to the density fluctuation. This effective Lagrangian can be related to the Anyon mean field, but can also be considered more generally to describe a universality class of superfluids and, when charged, of superconductors. We study the relevant physical properties, including the spectrum, the chirality features appearing in the polarization of scattered EM waves, and the peculiar response under a magnetic field, i.e. a peculiar kind of anisotropic Meissner effect.

cond-mat↗

arXiv1993

Anyon Mean Field as an Exact Limit of a Gauge Theory

We summarize a study of an Abelian gauge theory in 2+1 dimensions, the gauge field being coupled to nonrelativistic Fermions. The Action for the gauge field is a combination of the Maxwell term and a Chern-Simons (CS) term. We study the limit of vanishing Fermions' charge, keeping fixed the gauge field mass induced by the CS term. By considering a closed surface, in particular a torus to keep translational invariance, we show that the Fermions do not decouple completely from the gauge field, and in fact they behave as Anyons treated in the -translationally invariant formulation of the- Mean Field approximation. We describe the exact solution of this limiting case.

hep-th↗