16 research outputs found
Phase Diagram of the BCC S=1/2 Heisenberg Antiferromagnet with First and Second Neighbor Exchange
We use linked-cluster series expansions, both at T=0 and high temperature, to
analyse the phase structure of the spin-\half Heisenberg antiferromagnet with
competing first and second-neighbor interactions on the 3-dimensional
body-centred-cubic lattice. At zero temperature we find a first-order quantum
phase transition at between AF (Ne\'el)
and AF ordered phases. The high temperature series yield quite accurate
estimates of the bounding critical line for the AF phase, and an apparent
critical line for the AF phase, with a bicritical point at , . The possibility that this latter transition is
first-order cannot be excluded.Comment: 10 pages, 4 figure
Periodic One-Dimensional Hopping Model with one Mobile Directional Impurity
Analytic solution is given in the steady state limit for the system of Master
equations describing a random walk on one-dimensional periodic lattices with
arbitrary hopping rates containing one mobile, directional impurity (defect
bond). Due to the defect, translational invariance is broken, even if all other
rates are identical. The structure of Master equations lead naturally to the
introduction of a new entity, associated with the walker-impurity pair which we
call the quasi-walker. The velocities and diffusion constants for both the
random walker and impurity are given, being simply related to that of the
quasi-particle through physically meaningful equations. Applications in driven
diffusive systems are shown, and connections with the Duke-Rubinstein reptation
models for gel electrophoresis are discussed.Comment: 31 LaTex pages, 5 Postscript figures included, to appear in Journal
of Statistical Physic
A First Principles Estimate of Finite Size Effects in Quark-Gluon Plasma Formation
Using lattice simulations of quenched QCD we estimate the finite size effects
present when a gluon plasma equilibrates in a slab geometry, i.e., finite width
but large transverse dimensions. Significant differences are observed in the
free energy density for the slab when compared with bulk behavior. A small
shift in the critical temperature is also seen. The free energy required to
liberate heavy quarks relative to bulk is measured using Polyakov loops; the
additional free energy required is on the order of 30-40 MeV at 2-3 T_c.Comment: 10 pages, 5 figures, RevTeX; revised version includes comparison with
the Bjorken model and various small improvement
Spin Glass and Antiferromagnetic Behaviour in a Diluted fcc Antiferromagnet
We report on a Monte Carlo study of a diluted Ising antiferromagnet on a fcc
lattice. This is a typical model example of a highly frustrated
antiferromagnet, and we ask, whether sufficient random dilution of spins does
produce a spin glass phase. Our data strongly indicate the existence of a spin
glass transition for spin--concentration : We find a divergent spin
glass susceptibility and a divergent spin glass correlation length, whereas the
antiferromagnetic correlation length saturates in this regime. Furthermore, we
find a first order phase transition to an antiferromagnet for ,
which becomes continuous in the range . Finite size scaling is
employed to obtain critical exponents. We compare our results with experimental
systems as diluted frustrated antiferromagnets as .Comment: 29 pages (revtex) and 10 figures uuencoded and Z-compresse
Possible line of critical points for a random field Ising model in dimension 2
We study a particular random field Ising model in dimension 2 at 0 temperature. On each site the random field is either + ∞ with probability p/2, - ∞ with probability p/2 or 0 with probability 1 — p. Using finite size scaling arguments, we show that for small p, the average correlation function between two spins at distance R decreases like R-η( p) where the exponent η(p) = 2 πp + O(p2). The assumptions made to obtain this result and the possible generalizations to other random field models are discussedNous étudions un modèle d'Ising particulier en champ aléatoire. Sur chaque site, le champ aléatoire est soit + ∞ avec une probabilité p/2, - ∞ avec une probabilité p/2 ou 0 avec une probabilité 1 — p. En utilisant des arguments de lois d'échelle des systèmes finis, nous montrons que pour p petit, la fonction de corrélation moyenne de deux spins à une distance R décroît comme R-η(p) où l'exposant η(p) = 2 πp + O(p2). Les hypothèses faites pour obtenir ce résultat et les généralisations possibles à d'autres modèles d'Ising en champ aléatoire sont discutées