79 research outputs found
Spiral Spin Order and Transport Anisotropy in Underdoped Cuprates
We discuss the spiral spin density wave model and its application to explain
properties of underdoped LaSrCuO. We argue that the spiral
picture is theoretically well justified in the context of the extended
model, and then show that it can explain a number of observed features, such as
the location and symmetry of the incommensurate peaks in elastic neutron
scattering, as well as the in-plane resistivity anisotropy. A consistent
description of the low doping region (below 10% or so) emerges from the spiral
formulation, in which the holes show no tendency towards any type of charge
order and the physics is purely spin driven.Comment: 6 pages, 3 figures; Proceedings of the International Workshop on
Effective Models for Low-Dimensional Strongly Correlated Systems, September
2005, Peyresq, Franc
Thermodynamics of a gas of deconfined bosonic spinons in two dimensions
We consider the quantum phase transition between a Neel antiferromagnet and a
valence-bond solid (VBS) in a two-dimensional system of S=1/2 spins. Assuming
that the excitations of the critical ground state are linearly dispersing
deconfined spinons obeying Bose statistics, we derive expressions for the
specific heat and the magnetic susceptibility at low temperature T. Comparing
with quantum Monte Carlo results for the J-Q model, which is a candidate for a
deconfined Neel-VBS transition, we find excellent agreement, including a
previously noted logarithmic correction in the susceptibility. In our
treatment, this is a direct consequence of a confinement length scale Lambda
which is proportional to the correlation length xi raised to a non-trivial
power; Lambda ~ xi^(1+a) ~1/T^(1+a), with a>0 (with a approximately 0.2 in the
model).Comment: 4+ pages, 3 figures. v2: cosmetic changes onl
Weak antiferromagnetism and dimer order in quantum systems of coupled tetrahedra
We analyze the phases of an S=1/2 spin model on a lattice of coupled
tetrahedra. The presence of both Heisenberg and antisymmetric,
Dzyaloshinsky-Moriya interactions can lead to two types of symmetry-broken
states: non-magnetic dimer order and, unexpectedly, exotic 4 sub-lattice weak
antiferromagnetic order - a state with a generically small ordered moment and
non-zero chirality. External magnetic field also induces weak
antiferromagnetism co-existing with strong dimer correlations in the ground
state.
These states are formed as a result of broken Ising symmetries and exhibit a
number of unusual properties.Comment: 5 pages, 4 figures; final version to appear in Phys. Rev.
Theory of Anisotropic Hopping Transport due to Spiral Correlations in the Spin-Glass Phase of Underdoped Cuprates
We study the in-plane resistivity anisotropy in the spin-glass phase of the
high- cuprates, on the basis of holes moving in a spiral spin
background. This picture follows from analysis of the extended model with
Coulomb impurities. In the variable-range hopping regime the resistivity
anisotropy is found to have a maximum value of around 90%, and it decreases
with temperature, in excellent agreement with experiments in
LaSrCuO. In our approach the transport anisotropy is due to the
non-collinearity of the spiral spin state, rather than an intrinsic tendency of
the charges to self-organize.Comment: 5 pages, 4 figures; expanded versio
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