465 research outputs found
Finite size effects and magnetic order in the spin-1/2 honeycomb lattice compound InCu{2/3}V{1/3}O{3}
High field electron spin resonance, nuclear magnetic resonance and
magnetization studies addressing the ground state of the quasi two-dimensional
spin-1/2 honeycomb lattice compound InCu{2/3}V{1/3}O{3} are reported.
Uncorrelated finite size structural domains occurring in the honeycomb planes
are expected to inhibit long range magnetic order. Surprisingly, ESR data
reveal the development of two collinear antiferromagnetic (AFM) sublattices
below ~ 20 K whereas NMR results show the presence of the staggered internal
field. Magnetization data evidence a spin reorientation transition at ~ 5.7 T.
Quantum Monte-Carlo calculations show that switching on the coupling between
the honeycomb spin planes in a finite size cluster yields a Neel-like AFM spin
structure with a substantial staggered magnetization at finite temperatures.
This may explain the occurrence of a robust AFM state in InCu{2/3}V{1/3}O{3}
despite an unfavorable effect of structural disorder.Comment: revised version, accepted as a Rapid Communication in Phys. Rev. B
(2010
Neel order in the two-dimensional S=1/2 Heisenberg Model
The existence of Neel order in the S=1/2 Heisenberg model on the square
lattice at T=0 is shown using inequalities set up by Kennedy, Lieb and Shastry
in combination with high precision Quantum Monte Carlo data.Comment: 4 pages, 1 figur
Gapped Heisenberg spin chains in a field
We consider the fully anisotropic Heisenberg spin-1/2 antiferromagnet in a
uniform magnetic field, whose ground-state is characterized by broken spin
rotation symmetry and gapped spinon excitations. We expand on a recent
mean-field approach to the problem by incorporating fluctuations in a loop
expansion. Quantitative results for the magnetization, excitation gap and
specific heat are obtained. We compare our predictions with new DMRG and exact
diagonalization data and, for zero field, with the exact solution of the
spin chain from the Bethe Ansatz.Comment: 11 pages, 14 figure
Fermi Arc of Metallic Diagonal Stripes in High Tc Cuprates
Spectral weight is investigated for metallic diagonal stripe state in two
dimensional Hubbard model, and Fermi arc observed by angle-resolved
photoemission spectroscopy on LSCO is discussed. The Fermi arc coming from the
mid-gap state of diagonal stripe appears near
and equivalent position in the reciprocal space, and the gap opens below the
mid-gap state. We show how these spectral weight structure depends on the
phasing of stripes, i.e., site-centered or bond-centered stripes.Comment: 4 figure
Ion detection in the photoionization of a Rb Bose-Einstein condensate
Two-photon ionization of Rubidium atoms in a magneto-optical trap and a
Bose-Einstein condensate (BEC) is experimentally investigated. Using 100 ns
laser pulses, we detect single ions photoionized from the condenstate with a
35(10)% efficiency. The measurements are performed using a quartz cell with
external electrodes, allowing large optical access for BECs and optical
lattices.Comment: 14 pages, 7 figure
Avoided Critical Behavior in O(n) Systems
Long-range frustrating interactions, even if their strength is infinitesimal,
can give rise to a dramatic proliferations of ground or near-ground states. As
a consequence, the ordering temperature can exhibit a discontinuous drop as a
function of the frustration. A simple model of the doped Mott insulator, where
the short-range tendency of the holes to phase separate competes with
long-range Coulomb effects, exhibits this "avoided critical" behavior. This
model may serve as a paradigm for many other systems.Comment: 4 pages, 2 figure
On the Liaison Between Superconductivity and Phase Separation
Models of strongly correlated electrons that tend to phase separate are
studied including a long-range 1/r repulsive interaction. It is observed that
charge-density-wave states become stable as the strength of the 1/r term, , is increased. Due to this effect, the domain of stability of the
superconducting phases that appear near phase separation at is not enlarged by a 1/r interaction as naively expected. Nevertheless,
superconductivity exists in a wide region of parameter space, even if phase
separation is suppressed. Our results have implications for some theories of
the cuprates.Comment: 11 pages, 9 postscript figures are appende
Quantum non-equilibrium dynamics of Rydberg gases in the presence of dephasing noise of different strengths
In the presence of strong dephasing noise the dynamics of Rydberg gases becomes effectively classical, due to the rapid decay of quantum superpositions between atomic levels. Recently a great deal of attention has been devoted to the stochastic dynamics that emerges in that limit, revealing several interesting features, including kinetically constrained glassy behaviour, self-similarity and aggregation effects. However, the non-equilibrium physics of these systems, in particular in the regime where coherent and dissipative processes contribute on equal footing, is yet far from being understood. To explore this we study the dynamics of a small one-dimensional Rydberg lattice gas subject to dephasing noise by numerically integrating the quantum master equation. We interpolate between the coherent and the strongly dephased regime by defining a generalised concept of a blockade length. We find indications that the main features observed in the strongly dissipative limit persist when the dissipation is not strong enough to annihilate quantum coherences at the dynamically relevant time scales. These features include the existence of a time-dependent Rydberg blockade radius, and a growth of the density of excitations which is compatible with the power-law behaviour expected in the classical limit
Non-equilibrium fluctuations and metastability arising from non-additive interactions in dissipative multi-component Rydberg gases
We study the out-of-equilibrium dynamics of dissipative gases of atoms excited to two or more high-lying Rydberg states. This situation bears interesting similarities to classical binary (in general p-ary) mixtures of particles. The effective forces between the components are determined by the inter-level and intra-level interactions of Rydberg atoms. These systems permit to explore new parameter regimes which are physically inaccessible in a classical setting, for example one in which the mixtures exhibit non-additive interactions. In this situation the out-of-equilibrium evolution is characterized by the formation of metastable domains that reach partial equilibration long before the attainment of stationarity. In experimental settings with mesoscopic sizes, this collective behavior may in fact take the appearance of dynamic symmetry breaking
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