5,088 research outputs found
Signatures of superconducting gap inhomogeneities in optical properties
Scanning tunneling spectroscopy applied to the high- cuprates has
revealed significant spatial inhomogeneity on the nanoscale. Regions on the
order of a coherence length in size show variations of the magnitude of the
superconducting gap of order or more. An important unresolved question
is whether or not these variations are also present in the bulk, and how they
influence superconducting properties. As many theories and data analyses for
high- superconductivity assume spatial homogeneity of the gap magnitude,
this is a pressing question. We consider the far-infrared optical conductivity
and evaluate, within an effective medium approximation, what signatures of
spatial variations in gap magnitude are present in various optical quantities.
In addition to the case of d-wave superconductivity, relevant to the high-
cuprates, we have also considered s-wave gap symmetry in order to provide
expected signatures of inhomogeneities for superconductors in general. While
signatures of gap inhomogeneities can be strongly manifested in s-wave
superconductors, we find that the far-infrared optical conductivity in d-wave
is robust against such inhomogeneity.Comment: 8 pages, 7 figure
Bosonic D-branes at finite temperature with an external field
Bosonic boundary states at finite temperature are constructed as solutions of
boundary conditions at for bosonic open strings with a constant gauge
field coupled to the boundary. The construction is done in the
framework of thermo field dynamics where a thermal Bogoliubov transformation
maps states and operators to finite temperature. Boundary states are given in
terms of states from the direct product space between the Fock space of the
closed string and another identical copy of it. By analogy with zero
temperature, the boundary states heve the interpretation of -brane at
finite temperature. The boundary conditions admit two different solutions. The
entropy of the closed string in a -brane state is computed and analysed. It
is interpreted as the entropy of the -brane at finite temperature.Comment: 21 pages, Latex, revised version with minor corrections and
references added, to be published in Phys. Rev.
Symmetry Breaking in the Schr\"odinger Representation for Chern-Simons Theories
This paper discusses the phenomenon of spontaneous symmetry breaking in the
Schr\"odinger representation formulation of quantum field theory. The analysis
is presented for three-dimensional space-time abelian gauge theories with
either Maxwell, Maxwell-Chern-Simons, or pure Chern-Simons terms as the gauge
field contribution to the action, each of which leads to a different form of
mass generation for the gauge fields.Comment: 16pp, LaTeX , UCONN-94-
Two-point phase correlations of a one-dimensional bosonic Josephson junction
We realize a one-dimensional Josephson junction using quantum degenerate Bose
gases in a tunable double well potential on an atom chip. Matter wave
interferometry gives direct access to the relative phase field, which reflects
the interplay of thermally driven fluctuations and phase locking due to
tunneling. The thermal equilibrium state is characterized by probing the full
statistical distribution function of the two-point phase correlation.
Comparison to a stochastic model allows to measure the coupling strength and
temperature and hence a full characterization of the system
First results of the ROSEBUD Dark Matter experiment
Rare Objects SEarch with Bolometers UndergrounD) is an experiment which
attempts to detect low mass Weak Interacting Massive Particles (WIMPs) through
their elastic scattering off Al and O nuclei. It consists of three small
sapphire bolometers (of a total mass of 100 g) with NTD-Ge sensors in a
dilution refrigerator operating at 20 mK in the Canfranc Underground
Laboratory. We report in this paper the results of several runs (of about 10
days each) with successively improved energy thresholds, and the progressive
background reduction obtained by improvement of the radiopurity of the
components and subsequent modifications in the experimental assembly, including
the addition of old lead shields. Mid-term plans and perspectives of the
experiment are also presented.Comment: 14 pages, 8 figures, submitted to Astroparticle Physic
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