283 research outputs found
Feynman path-integral approach to the QED3 theory of the pseudogap
In this work the connection between vortex condensation in a d-wave
superconductor and the QED gauge theory of the pseudogap is elucidated. The
approach taken circumvents the use of the standard Franz-Tesanovic gauge
transformation, borrowing ideas from the path-integral analysis of the
Aharonov-Bohm problem. An essential feature of this approach is that
gauge-transformations which are prohibited on a particular multiply-connected
manifold (e.g. a superconductor with vortices) can be successfully performed on
the universal covering space associated with that manifold.Comment: 15 pages, 1 Figure. Int. J. Mod. Phys. B 17, 4509 (2003). Minor
changes from previous versio
Non-local order in gapless systems: Entanglement Spectrum in Spin Chains
We show that the entanglement spectrum can be used to define non-local order
in gapless spin systems. We find a gap that fully separates a series of
generic, high `entanglement energy' levels, from a flat band of levels with
specific multiplicities that uniquely define the ground-state, and remains
finite in the thermodynamic limit. We pick the appropriate set of quantum
numbers, and then partition the system in this space. This partition
corresponds to a very non-local real-space cut. Despite the fact that the
Laughlin state is bulk gapped while the antiferromagnetic spin chain state is
bulk gapless, we show that the S=1/2 Heisenberg antiferromagnet in one
dimension has an entanglement spectrum almost identical to that of the Laughlin
Fractional Quantum Hall state in two dimensions, revealing the similar field
theory of their low-energy edge and bulk excitations respectively.Comment: 4.5 pages, 3 figures; submitted to PRL on 10/08/09; revised version
plus supplementary materia
Comment on "Statistical Mechanics of Non-Abelian Chern-Simons Particles"
The second virial coefficient for non-Abelian Chern-Simons particles is
recalculated. It is shown that the result is periodic in the flux parameter
just as in the Abelian theory.Comment: 3 pages, latex fil
Spin 3/2 dimer model
We present a parent Hamiltonian for weakly dimerized valence bond solid
states for arbitrary half-integral S. While the model reduces for S=1/2 to the
Majumdar-Ghosh Hamiltonian we discuss this model and its properties for S=3/2.
Its degenerate ground state is the most popular toy model state for discussing
dimerization in spin 3/2 chains. In particular, it describes the impurity
induced dimer phase in Cr8Ni as proposed recently. We point out that the
explicit construction of the Hamiltonian and its main features apply to
arbitrary half-integral spin S.Comment: 5+ pages, 6 figures; to appear in Europhysics Letter
Exact Study of the 1D Boson Hubbard Model with a Superlattice Potential
We use Quantum Monte Carlo simulations and exact diagonalization to explore
the phase diagram of the Bose-Hubbard model with an additional superlattice
potential. We first analyze the properties of superfluid and insulating phases
present in the hard-core limit where an exact analytic treatment is possible
via the Jordan-Wigner transformation. The extension to finite on-site
interaction is achieved by means of quantum Monte Carlo simulations. We
determine insulator/superfluid phase diagrams as functions of the on-site
repulsive interaction, superlattice potential strength, and filling, finding
that insulators with fractional occupation numbers, which are present in the
hard-core case, extend deep into the soft-core region. Furthermore, at integer
fillings, we find that the competition between the on-site repulsion and the
superlattice potential can produce a phase transition between a Mott insulator
and a charge density wave insulator, with an intermediate superfluid phase. Our
results are relevant to the behavior of ultracold atoms in optical
superlattices which are beginning to be studied experimentally.Comment: 13 pages, 23 figure
Phase Diagram of Half Doped Manganites
An analysis of the properties of half-doped manganites is presented. We build
up the phase diagram of the system combining a realistic calculation of the
electronic properties and a mean field treatment of the temperature effects.
The electronic structure of the manganites are described with a double exchange
model with cooperative Jahn-Teller phonons and antiferromagnetic coupling
between the core spins. At zero temperature a variety of electronic phases
as ferromagnetic (FM) charge ordered (CO) orbital ordered (OO), CE-CO-OO and FM
metallic, are obtained. By raising the temperature the CE-CO-OO phase becomes
paramagnetic (PM), but depending on the electron-phonon coupling and the
exchange coupling the transition can be direct or trough intermediate states: a
FM disorder metallic, a PM-CO-OO or a FM-CO-OO. We also discus the nature of
the high temperature PM phase in the regime of finite electron phonon coupling.
In this regime half of the oxygen octahedra surrounding the ions are
distorted. In the weak coupling regime the octahedra are slightly deformed and
only trap a small amount of electronic charge, rendering the system metallic
consequentially. However in the strong coupling regime the octahedra are
strongly distorted, the charge is fully localized in polarons and the system is
insulator.Comment: 10 pagses, 9 figures include
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