9,210 research outputs found
Vortex-boson duality in four space-time dimensions
A continuum version of the vortex-boson duality in (3+1) dimensions is
formulated and its implications studied in the context of a pair Wigner crystal
in underdoped cuprate superconductors. The dual theory to a phase fluctuating
superconductor (or superfluid) is shown to be a theory of bosonic strings
interacting through a Kalb-Ramond rank-2 tensorial gauge field. String
condensation produces Higgs mass for the gauge field and the expected Wigner
crystal emerges as an interesting space-time analog of the Abrikosov lattice.Comment: 4 pages REVTeX; for related work and info visit
http://www.physics.ubc.ca/~fran
Surface magnetic ordering in topological insulators with bulk magnetic dopants
We show that a three dimensional topological insulator doped with magnetic
impurities in the bulk can have a regime where the surface is magnetically
ordered but the bulk is not. This is in contrast to conventional materials
where bulk ordered phases are typically more robust than surface ordered
phases. The difference originates from the topologically protected gapless
surface states characteristic of topological insulators. We study the problem
using a mean field approach in two concrete models that give the same
qualitative result, with some interesting differences. Our findings could help
explain recent experimental results showing the emergence of a spectral gap in
the surface state of Bi2Se3 doped with Mn or Fe atoms, but with no measurable
bulk magnetism.Comment: 8 pages, 6 figure
Discrete Spectra of Semirelativistic Hamiltonians
We review various attempts to localize the discrete spectra of
semirelativistic Hamiltonians of the form H = \beta \sqrt{m^2 + p^2} + V(r)
(w.l.o.g. in three spatial dimensions) as entering, for instance, in the
spinless Salpeter equation. Every Hamiltonian in this class of operators
consists of the relativistic kinetic energy \beta \sqrt{m^2 + p^2} (where \beta
> 0 allows for the possibility of more than one particles of mass m) and a
spherically symmetric attractive potential V(r), r = |x|. In general, accurate
eigenvalues of a nonlocal Hamiltonian operator can only be found by the use of
a numerical approximation procedure. Our main emphasis, however, is on the
derivation of rigorous semi-analytical expressions for both upper and lower
bounds to the energy levels of such operators. We compare the bounds obtained
within different approaches and present relationships existing between the
bounds.Comment: 21 pages, 3 figure
On the integral cohomology of smooth toric varieties
Let be a smooth, not necessarily compact toric variety. We show
that a certain complex, defined in terms of the fan , computes the
integral cohomology of , including the module structure over the
homology of the torus. In some cases we can also give the product. As a
corollary we obtain that the cycle map from Chow groups to integral Borel-Moore
homology is split injective for smooth toric varieties. Another result is that
the differential algebra of singular cochains on the Borel construction of
is formal.Comment: 10 page
Instantaneous Bethe-Salpeter equation: improved analytical solution
Studying the Bethe-Salpeter formalism for interactions instantaneous in the
rest frame of the bound states described, we show that, for bound-state
constituents of arbitrary masses, the mass of the ground state of a given spin
may be calculated almost entirely analytically with high accuracy, without the
(numerical) diagonalization of the matrix representation obtained by expansion
of the solutions over a suitable set of basis states.Comment: 7 page
On nonlinear susceptibility in supercooled liquids
In this paper, we discuss theoretically the behavior of the four point
nonlinear susceptibility and its associated correlation length for supercooled
liquids close to the Mode Coupling instability temperature . We work in
the theoretical framework of the glass transition as described by mean field
theory of disordered systems, and the hypernetted chain approximation. Our
results give an interpretation framework for recent numerical findings on
heterogeneities in supercooled liquid dynamics.Comment: Proceedings of the Conference "Unifying Concepts in Glass Physics"
ICTP, Trieste, 15 - 18 September 199
Kob-Andersen model: a non-standard mechanism for the glassy transition
We present new results reflecting the analogies between the Kob-Andersen
model and other glassy systems. Studying the stability of the blocked
configurations above and below the transition we also give arguments that
supports their relevance for the glassy behaviour of the model.
However we find, surprisingly, that the organization of the phase space of
the system is different from the well known organization of other mean-field
spin glasses and structural glasses.Comment: New reference added and one update
Instantaneous Bethe-Salpeter Equation: Analytic Approach for Nonvanishing Masses of the Bound-State Constituents
The instantaneous Bethe-Salpeter equation, derived from the general
Bethe-Salpeter formalism by assuming that the involved interaction kernel is
instantaneous, represents the most promising framework for the description of
hadrons as bound states of quarks from first quantum-field-theoretic
principles, that is, quantum chromodynamics. Here, by extending a previous
analysis confined to the case of bound-state constituents with vanishing
masses, we demonstrate that the instantaneous Bethe-Salpeter equation for
bound-state constituents with (definitely) nonvanishing masses may be converted
into an eigenvalue problem for an explicitly - more precisely, algebraically -
known matrix, at least, for a rather wide class of interactions between these
bound-state constituents. The advantages of the explicit knowledge of this
matrix representation are self-evident.Comment: 12 Pages, LaTeX, 1 figur
Duality and the vibrational modes of a Cooper-pair Wigner crystal
When quantum fluctuations in the phase of the superconducting order parameter
destroy the off-diagonal long range order, duality arguments predict the
formation of a Cooper pair crystal. This effect is thought to be responsible
for the static checkerboard patterns observed recently in various underdoped
cuprate superconductors by means of scanning tunneling spectroscopy. Breaking
of the translational symmetry in such a Cooper pair Wigner crystal may, under
certain conditions, lead to the emergence of low lying transverse vibrational
modes which could then contribute to thermodynamic and transport properties at
low temperatures. We investigate these vibrational modes using a continuum
version of the standard vortex-boson duality, calculate the speed of sound in
the Cooper pair Wigner crystal and deduce the associated specific heat and
thermal conductivity. We then suggest that these modes could be responsible for
the mysterious bosonic contribution to the thermal conductivity recently
observed in strongly underdoped ultraclean single crystals of YBCO tuned across
the superconductor-insulator transition.Comment: 14 pages; 3 figures; corrected the sample size value; version 3 to
appear in PR
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