637 research outputs found
On Defect-Mediated Transitions in Bosonic Planar Lattices
We discuss the finite-temperature properties of Bose-Einstein condensates
loaded on a 2D optical lattice. In an experimentally attainable range of
parameters the system is described by the XY model, which undergoes a
Berezinskii-Kosterlitz-Thouless (BKT) transition driven by the vortex pair
unbinding. The interference pattern of the expanding condensates provides the
experimental signature of the BKT transition: near the critical temperature,
the k=0 component of the momentum distribution sharply decreases
Adiabatic Control of the Electron Phase in a Quantum Dot
A Berry phase can be added to the wavefunction of an isolated quantum dot by
adiabatically modulating a nonuniform electric field along a time-cycle. The
dot is tuned close to a three-level degeneracy, which provides a wide range of
possibilities of control. We propose to detect the accumulated phase by
capacitively coupling the dot to a double-path inteferometer. The effective
Hamiltonian for the phase-sensitive coupling is discussed in detail.Comment: 14 pages, 2 .eps figure
Self-Consistent Mean-Field Theory for Frustrated Josephson Junction Arrays
We review the self-consistent mean-field theory for charge-frustrated
Josephson junction arrays. Using (\phi is the phase of the
superconducting wavefunction) as order parameter and imposing the
self-consistency condition, we compute the phase boundary line between the
superconducting region ( not equal to zero) and the insulating one
( = 0). For a uniform offset charge q=e the superconducting phase
increases with respect to the situation in which q=0. Here, we generalize the
self-consistent mean-field theory to include the effects induced by a random
distribution of offset charges and/or of diagonal self-capacitances. For most
of the phase diagram, our results agree with the outcomes of Quantum Monte
Carlo simulations as well as with previous studies using the path-integral
approach.Comment: Presented by F. P. Mancini at the Conference "Highlights in Condensed
Matter Physics", May 9-11 2003, Salerno, Ital
Superconductors with Topological Order and their Realization in Josephson Junction Arrays
We will describe a new superconductivity mechanism, proposed by the authors
in [1], which is based on a topologically ordered ground state rather than on
the usual Landau mechanism of spontaneous symmetry breaking. Contrary to anyon
superconductivity it works in any dimension and it preserves P-and
T-invariance. In particular we will discuss the low-energy effective field
theory, what would be the Landau-Ginzburg formulation for conventional
superconductors.Comment: invited review, to appear in "Superconductivity Research Advances",
Nova Publishers, 32 page
From topological insulators to superconductors and Confinement
Topological matter in 3D is characterized by the presence of a topological BF
term in its long-distance effective action. We show that, in 3D, there is
another marginal term that must be added to the action in order to fully
determine the physical content of the model. The quantum phase structure is
governed by three parameters that drive the condensation of topological
defects: the BF coupling, the electric permittivity and the magnetic
permeability of the material. For intermediate levels of electric permittivity
and magnetic permeability the material is a topological insulator. We predict,
however, new states of matter when these parameters cross critical values: a
topological superconductor when electric permittivity is increased and magnetic
permeability is lowered and a charge confinement phase in the opposite case of
low electric permittivity and high magnetic permeability. Synthetic topological
matter may be fabricated as 3D arrays of Josephson junctions.Comment: 5 pages, no figures, few references added, typos corrected and few
comments adde
Superconducting Topological Fluids in Josephson Junction Arrays
We argue that the frustrated Josephson junction arrays may support a
topologically ordered superconducting ground state, characterized by a
non-trivial ground state degeneracy on the torus. This superconducting quantum
fluid provides an explicit example of a system in which superconductivity
arises from a topological mechanism rather than from the usual Landau-Ginzburg
mechanism.Comment: 4 page
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