6,645 research outputs found
Distribution of sizes of erased loops for loop-erased random walks
We study the distribution of sizes of erased loops for loop-erased random
walks on regular and fractal lattices. We show that for arbitrary graphs the
probability of generating a loop of perimeter is expressible in
terms of the probability of forming a loop of perimeter when a
bond is added to a random spanning tree on the same graph by the simple
relation . On -dimensional hypercubical lattices,
varies as for large , where for , where
z is the fractal dimension of the loop-erased walks on the graph. On
recursively constructed fractals with this relation is modified
to , where is the hausdorff and
is the spectral dimension of the fractal.Comment: 4 pages, RevTex, 3 figure
Quasiadiabatic dynamics of ultracold bosonic atoms in a one-dimensional optical superlattice
We study the quasiadiabatic dynamics of a one-dimensional system of ultracold
bosonic atoms loaded in an optical superlattice. Focusing on a slow linear
variation in time of the superlattice potential, the system is driven from a
conventional Mott insulator phase to a superlattice-induced Mott insulator,
crossing in between a gapless critical superfluid region. Due to the presence
of a gapless region, a number of defects depending on the velocity of the
quench appear. Our findings suggest a power-law dependence similar to the
Kibble-Zurek mechanism for intermediate values of the quench rate. For the
temporal ranges of the quench dynamics that we considered, the scaling of
defects depends nontrivially on the width of the superfluid region.Comment: 6 Pages, 4 Figure
Two simple models of classical heat pumps
Motivated by recent studies on models of particle and heat quantum pumps, we
study similar simple classical models and examine the possibility of heat
pumping. Unlike many of the usual ratchet models of molecular engines, the
models we study do not have particle transport. We consider a two-spin system
and a coupled oscillator system which exchange heat with multiple heat
reservoirs and which are acted upon by periodic forces. The simplicity of our
models allows accurate numerical and exact solutions and unambiguous
interpretation of results. We demonstrate that while both our models seem to be
built on similar principles, one is able to function as a heat pump (or engine)
while the other is not.Comment: 4 pages, 4 figure
Fast trimers in one-dimensional extended Fermi-Hubbard model
We consider a one-dimensional two component extended Fermi-Hubbard model with
nearest neighbor interactions and mass imbalance between the two species. We
study the stability of trimers, various observables for detecting them, and
expansion dynamics. We generalize the definition of the trimer gap to include
the formation of different types of clusters originating from nearest neighbor
interactions. Expansion dynamics reveal rapidly propagating trimers, with
speeds exceeding doublon propagation in strongly interacting regime. We present
a simple model for understanding this unique feature of the movement of the
trimers, and we discuss the potential for experimental realization.Comment: 10 pages, 10 figure
Enhanced conduction band density of states in intermetallic EuTSi (T=Rh, Ir)
We report on the physical properties of single crystalline EuRhSi and
polycrystalline EuIrSi, inferred from magnetisation, electrical transport,
heat capacity and Eu M\"ossbauer spectroscopy. These previously known
compounds crystallise in the tetragonal BaNiSn-type structure. The single
crystal magnetisation in EuRhSi has a strongly anisotropic behaviour at 2 K
with a spin-flop field of 13 T, and we present a model of these magnetic
properties which allows the exchange constants to be determined. In both
compounds, specific heat shows the presence of a cascade of two close
transitions near 50 K, and the Eu M\"ossbauer spectra demonstrate that
the intermediate phase has an incommensurate amplitude modulated structure. We
find anomalously large values, with respect to other members of the series, for
the RKKY N\'eel temperature, for the spin-flop field (13 T), for the spin-wave
gap ( 20-25 K) inferred from both resistivity and specific heat data,
for the spin-disorder resistivity in EuRhSi ( Ohm.cm) and
for the saturated hyperfine field (52 T). We show that all these quantities
depend on the electronic density of states at the Fermi level, implying that
the latter must be strongly enhanced in these two materials. EuIrSi
exhibits a giant magnetoresistance ratio, with values exceeding 600 % at 2 K in
a field of 14 T.Comment: 6 pages, 8 figure
Spin glasses in the limit of an infinite number of spin components
We consider the spin glass model in which the number of spin components, m,
is infinite. In the formulation of the problem appropriate for numerical
calculations proposed by several authors, we show that the order parameter
defined by the long-distance limit of the correlation functions is actually
zero and there is only "quasi long range order" below the transition
temperature. We also show that the spin glass transition temperature is zero in
three dimensions.Comment: 9 pages, 13 figure
Quenched Averages for self-avoiding walks and polygons on deterministic fractals
We study rooted self avoiding polygons and self avoiding walks on
deterministic fractal lattices of finite ramification index. Different sites on
such lattices are not equivalent, and the number of rooted open walks W_n(S),
and rooted self-avoiding polygons P_n(S) of n steps depend on the root S. We
use exact recursion equations on the fractal to determine the generating
functions for P_n(S), and W_n(S) for an arbitrary point S on the lattice. These
are used to compute the averages and over different positions of S. We find that the connectivity constant
, and the radius of gyration exponent are the same for the annealed
and quenched averages. However, , and , where the exponents
and take values different from the annealed case. These
are expressed as the Lyapunov exponents of random product of finite-dimensional
matrices. For the 3-simplex lattice, our numerical estimation gives ; and , to be
compared with the annealed values and .Comment: 17 pages, 10 figures, submitted to Journal of Statistical Physic
Magnetic behaviour of PrPd2B2C
We have synthesized a new quaternary borocarbide PrPdBC and
measured its magnetization, electrical resistivity and specific heat. The
compound crystallizes in the LuNiBC-type tetragonal structure
(space group {\it I4/mmm}). Above 100 K the magnetic susceptibility follows
Curie-Weiss behavior with effective moment = 3.60 , which
is very close to the value expected for Pr ions. We do not find evidence
for magnetic or superconducting transition down to 0.5 K. Specific heat
exhibits a broad Schottky type anomaly with a peak at 24 K, very likely related
to crystal electric field (CEF) excitation. The magnetic properties suggest the
presence of a singlet CEF ground state leading to a Van-Vleck paramagnetic
ground state.Comment: 2 pages, 2 figure
Comment on ``Can Disorder Induce a Finite Thermal Conductivity in 1D Lattices?''
In a recent paper [Phys. Rev. Lett. 86, 63 (2001)], Li et al have reported
that the nonequilibrium heat conducting steady state of a disordered harmonic
chain is not unique. In this comment we point out that for a large class of
stochastic heat baths the uniqueness of the steady state can be proved, and
therefore the findings of Li et al could be either due to their use of
deterministic heat baths or insufficient equilibration times in the
simulations. We give a simple example where the uniquness of the steady state
can be explicitly demonstrated.Comment: 1 page, 1 figure, accepted for publication in Phys. Rev. Let
- …