3,810 research outputs found
The Correlation Functions of the XXZ Heisenberg Chain for Zero or Infinite Anisotropy and Random Walks of Vicious Walkers
The XXZ Heisenberg chain is considered for two specific limits of the
anisotropy parameter: \Dl\to 0 and \Dl\to -\infty. The corresponding wave
functions are expressed by means of the symmetric Schur functions. Certain
expectation values and thermal correlation functions of the ferromagnetic
string operators are calculated over the base of N-particle Bethe states. The
thermal correlator of the ferromagnetic string is expressed through the
generating function of the lattice paths of random walks of vicious walkers. A
relationship between the expectation values obtained and the generating
functions of strict plane partitions in a box is discussed. Asymptotic estimate
of the thermal correlator of the ferromagnetic string is obtained in the limit
of zero temperature. It is shown that its amplitude is related to the number of
plane partitions.Comment: 22 pages, 1 figure, LaTe
Zero Range Process and Multi-Dimensional Random Walks
The special limit of the totally asymmetric zero range process of the
low-dimensional non-equilibrium statistical mechanics described by the
non-Hermitian Hamiltonian is considered. The calculation of the conditional
probabilities of the model are based on the algebraic Bethe ansatz approach. We
demonstrate that the conditional probabilities may be considered as the
generating functions of the random multi-dimensional lattice walks bounded by a
hyperplane. This type of walks we call the walks over the multi-dimensional
simplicial lattices. The answers for the conditional probability and for the
number of random walks in the multi-dimensional simplicial lattice are
expressed through the symmetric functions
Correlation Functions of XX0 Heisenberg Chain, q-Binomial Determinants, and Random Walks
The XX0 Heisenberg model on a cyclic chain is considered. The representation
of the Bethe wave functions via the Schur functions allows to apply the
well-developed theory of the symmetric functions to the calculation of the
thermal correlation functions. The determinantal expressions of the
form-factors and of the thermal correlation functions are obtained. The
q-binomial determinants enable the connection of the form-factors with the
generating functions both of boxed plane partitions and of self-avoiding
lattice paths. The asymptotical behavior of the thermal correlation functions
is studied in the limit of low temperature provided that the characteristic
parameters of the system are large enough.Comment: 27 pages, 2 figures, LaTe
Probing quantum-mechanical level repulsion in disordered systems by means of time-resolved selectively-excited resonance fluorescence
We argue that the time-resolved spectrum of selectively-excited resonance
fluorescence at low temperature provides a tool for probing the
quantum-mechanical level repulsion in the Lifshits tail of the electronic
density of states in a wide variety of disordered materials. The technique,
based on detecting the fast growth of a fluorescence peak that is red-shifted
relative to the excitation frequency, is demonstrated explicitly by simulations
on linear Frenkel exciton chains.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
Low-temperature dynamics of weakly localized Frenkel excitons in disordered linar chains
We calculate the temperature dependence of the fluorescence Stokes shift and
the fluorescence decay time in linear Frenkel exciton systems resulting from
the thermal redistribution of exciton population over the band states. The
following factors, relevant to common experimental conditions, are accounted
for in our kinetic model: (weak) localization of the exciton states by static
disorder, coupling of the localized excitons to vibrations in the host medium,
a possible non-equilibrium of the subsystem of localized Frenkel excitons on
the time scale of the emission process, and different excitation conditions
(resonant or non resonant). A Pauli master equation, with microscopically
calculated transition rates, is used to describe the redistribution of the
exciton population over the manifold of localized exciton states. We find a
counterintuitive non-monotonic temperature dependence of the Stokes shift. In
addition, we show that depending on experimental conditions, the observed
fluorescence decay time may be determined by vibration-induced intra-band
relaxation, rather than radiative relaxation to the ground state. The model
considered has relevance to a wide variety of materials, such as linear
molecular aggregates, conjugated polymers, and polysilanes.Comment: 15 pages, 8 figure
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