86 research outputs found
Spin-Peierls states of quantum antiferromagnets on the lattice
We discuss the quantum paramagnetic phases of Heisenberg antiferromagnets on
the 1/5-depleted square lattice found in . The possible phases of
the quantum dimer model on this lattice are obtained by a mapping to a
quantum-mechanical height model. In addition to the ``decoupled'' phases found
earlier, we find a possible intermediate spin-Peierls phase with
spontaneously-broken lattice symmetry. Experimental signatures of the different
quantum paramagnetic phases are discussed.Comment: 9 pages; 2 eps figure
Renormalization Group for Large N Strongly Commensurate Dirty Boson Model
The large N sigma model, in D<4 space-time dimensions, with disorder a
function of d space dimensions, is analyzed via a renormalization group
treatment. Critical exponents for average quantities are calculated, first to
lowest order and then to all orders, in . In particular, it
is found that . When D=d+1, this model is equivalent to a large N
limit of the strongly commensurate dirty boson problem.Comment: 16 pages, 4 figures, to be published in PR
Renormalization Group Approach to the Infrared Behavior of a Zero-Temperature Bose System
We exploit the renormalization-group approach to establish the {\em exact}
infrared behavior of an interacting Bose system at zero temperature. The
local-gauge symmetry in the broken-symmetry phase is implemented through the
associated Ward identities, which reduce the number of independent running
couplings to a single one. For this coupling the -expansion can be
controlled to all orders in (). For spatial dimensions the Bogoliubov fixed point is unstable towards a different fixed point
characterized by the divergence of the longitudinal correlation function. The
Bogoliubov linear spectrum, however, is found to be independent from the
critical behavior of this correlation function, being exactly constrained by
Ward identities. The new fixed point properly gives a finite value of the
coupling among transverse fluctuations, but due to virtual intermediate
longitudinal fluctuations the effective coupling affecting the transverse
correlation function flows to zero. As a result, no transverse anomalous
dimension is present. This treatment allows us to recover known results for the
quantum Bose gas in the context of a unifying framework and also to reveal the
non-trivial skeleton structure of its perturbation theory.Comment: 21 page
Terawatt, Joule-Class Pulsed THz Sources from Microchannel Targets
Production of terawatt, joule class THz radiation sources from microchannel
targets driven with 100s of joule, picosecond lasers is reported. THz sources
of this magnitude are useful for non-linear pumping of matter and for charged
particle acceleration and manipulation. Microchannel targets demonstrate
increased conversion efficiency compared to planar foil targets, with laser
energy to THz energy conversion up to 0.9 percent.Comment: 9 pages, 2 figure
The density dependence of the transition temperature in a homogenous Bose flui
Transition temperature data obtained as a function of particle density in the
He-Vycor system are compared with recent theoretical calculations for 3D
Bose condensed systems. In the low density dilute Bose gas regime we find, in
agreement with theory, a positive shift in the transition temperature of the
form . At higher densities a maximum is
found in the ratio of for a value of the interaction parameter,
na, that is in agreement with path-integral Monte Carlo calculations.Comment: 4 pages, 3 figure
Two-particle pairing and phase separation in a two-dimensional Bose-gas with one or two sorts of bosons
We present a phase diagram for a dilute two-dimensional Bose-gas on a
lattice. For one sort of boson we consider a realistic case of the van der
Waals interaction between particles with a strong hard-core repulsion and a
van der Waals attractive tail . For , being a hopping
amplitude, the phase diagram of the system contains regions of the usual
one-particle Bose-Einstein condensation (BEC). However for we have total
phase separation on a Mott-Hubbard Bose solid and a dilute Bose gas. For two
sorts of structureless bosons described by the two band Hubbard model an s-wave
pairing of the two bosons of different sort is possible.
The results we obtained should be important for different Bose systems,
including submonolayers of He, excitons in semiconductors, Schwinger bosons
in magnetic systems and holons in HTSC. In the HTSC case a possibility of
two-holon pairing in the slave-bosons theories of superconductivity can restore
a required charge of a Cooper pair.Comment: 10 pages, 2 figure
Interaction effects in non-Hermitian models of vortex physics
Vortex lines in superconductors in an external magnetic field slightly tilted
from randomly-distributed parallel columnar defects can be modeled by a system
of interacting bosons in a non-Hermitian vector potential and a random scalar
potential. We develop a theory of the strongly-disordered non-Hermitian boson
Hubbard model using the Hartree-Bogoliubov approximation and apply it to
calculate the complex energy spectra, the vortex tilt angle and the tilt
modulus of (1+1)-dimensional directed flux line systems. We construct the phase
diagram associated with the flux-liquid to Bose-glass transition and find that,
close to the phase boundary, the tilted flux liquid phase is characterized by a
band of localized excitations, with two mobility edges in its low-energy
spectrum.Comment: 19 pages, 19 figures, To appear in Phys. Rev.
Rotating Shallow Water Dynamics: Extra Invariant and the Formation of Zonal Jets
We show that rotating shallow water dynamics possesses an approximate
(adiabatic-type) positive quadratic invariant, which exists not only at
mid-latitudes (where its analogue in the quasigeostrophic equation has been
previously investigated), but near the equator as well (where the
quasigeostrophic equation is inapplicable). Deriving the extra invariant, we
find "small denominators" of two kinds: (1) due to the triad resonances (as in
the case of the quasigeostrophic equation) and (2) due to the equatorial limit,
when the Rossby radius of deformation becomes infinite. We show that the "small
denominators" of both kinds can be canceled. The presence of the extra
invariant can lead to the generation of zonal jets. We find that this tendency
should be especially pronounced near the equator. Similar invariant occurs in
magnetically confined fusion plasmas and can lead to the emergence of zonal
flows.Comment: 29 pages, 4 figure
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