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One-dimensional Ising ferromagnet frustrated by long-range interactions at finite temperatures
We consider a one-dimensional lattice of Ising-type variables where the
ferromagnetic exchange interaction J between neighboring sites is frustrated by
a long-ranged anti-ferromagnetic interaction of strength g between the sites i
and j, decaying as |i-j|^-alpha, with alpha>1. For alpha smaller than a certain
threshold alpha_0, which is larger than 2 and depends on the ratio J/g, the
ground state consists of an ordered sequence of segments with equal length and
alternating magnetization. The width of the segments depends on both alpha and
the ratio J/g. Our Monte Carlo study shows that the on-site magnetization
vanishes at finite temperatures and finds no indication of any phase
transition. Yet, the modulation present in the ground state is recovered at
finite temperatures in the two-point correlation function, which oscillates in
space with a characteristic spatial period: The latter depends on alpha and J/g
and decreases smoothly from the ground-state value as the temperature is
increased. Such an oscillation of the correlation function is exponentially
damped over a characteristic spatial scale, the correlation length, which
asymptotically diverges roughly as the inverse of the temperature as T=0 is
approached. This suggests that the long-range interaction causes the Ising
chain to fall into a universality class consistent with an underlying
continuous symmetry. The e^(Delta/T)-temperature dependence of the correlation
length and the uniform ferromagnetic ground state, characteristic of the g=0
discrete Ising symmetry, are recovered for alpha > alpha_0.Comment: 12 pages, 7 figure