Oron Zachar
University of California, Los Angeles
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Featured researches published by Oron Zachar.
Physical Review B | 1998
Oron Zachar; Steven A. Kivelson; V. J. Emery
We consider a Landau theory of coupled charge and spin-density-wave order parameters as a simple model for the ordering that has been observed experimentally in the La{sub 2}NiO{sub 4} and La{sub 2}CuO{sub 4} families of doped antiferromagnets. The period of the charge-density wave is generically half that of the spin-density wave, or equivalently the charges form antiphase domain walls in the antiferromagnetic order. A sharp distinction exists between the case in which the ordering is primarily charge driven (which produces a sequence of transitions in qualitative agreement with experiment) or spin driven (which does not). We also find that stripes with noncollinear spin order (i.e., spiral phases) are possible in a region of the phase diagram where the transition is spin driven; the spiral is circular only when there is no charge order, and is otherwise elliptical with an eccentricity proportional to the magnitude of the charge order. {copyright} {ital 1998} {ital The American Physical Society}
Physical Review Letters | 1996
Oron Zachar; Steven A. Kivelson; V. J. Emery
A one-dimensional electron gas interacting with a {ital lattice} of Kondo scattering centers is solved in a particular limit. A variety of exact results are obtained for commensurate and incommensurate fillings, for impurity vacancy states, and for the commensurate-incommensurate transition. {copyright} {ital 1996 The American Physical Society.}
Physical Review Letters | 2004
Leonid P. Pryadko; Steven A. Kivelson; Oron Zachar
We analyze the high-temperature behavior of the susceptibilities towards a number of possible ordered states in the t-J-V model using the high-temperature series expansion. From all diagrams with up to ten edges, reliable results are obtained down to temperatures of order J, or (with some optimism) to J/2. In the unphysical regime, t<J, large superconducting susceptibilities are found which, moreover, increase with decreasing temperatures, but for t>J, these susceptibilities are small and decreasing with decreasing temperature; this suggests that the t-J model does not support high-temperature superconductivity. We also find modest evidence of a tendency toward nematic and d-density wave orders.
Physical Review B | 1999
V. J. Emery; Steven A. Kivelson; Oron Zachar
The classification of the ground-state phases of complex one-dimensional electronic systems is considered in the context of a fixed-point strategy. Examples are multichain Hubbard models, the Kondo-Heisenberg model, and the one-dimensional electron gas in an active environment. It is shown that, in order to characterize the low-energy physics, it is necessary to analyze the perturbative stability of the possible fixed points, to identify all discrete broken symmetries, and to specify the quantum numbers and elementary wave vectors of the gapless excitations. Many previously proposed exotic phases of multichain Hubbard models are shown to be unstable because of the {open_quotes}spin-gap proximity effect.{close_quotes} A useful tool in this analysis is a generalization of Luttinger{close_quote}s theorem, which shows that there is a gapless even-charge mode in any incommensurate {ital N}-component system. {copyright} {ital 1999} {ital The American Physical Society}
Cognitive Science | 1998
Nili Mandelblit; Oron Zachar
We suggest a common ground for alternative proposals in different domains of cognitive science which have previously seemed to have little in common. The underlying common theme is associated with a redefinition of the basic unit of analysis in each domain of thought. Our framework suggests a definition of unity which is based not on inherent properties of the elements constituting the unit, but rather on dynamic patterns of correlation across the elements. We introduce a set of features that characterize the new dynamic units, and distinguish them from traditional units of analysis. A conceptual connection is made with the identification of elementary units in modern physics theories, as well as with concepts and structures in the study of complex dynamical systems and connectionism. The paper analyses the evolution of the concept of unit in different domains of thought in cognitive science, and examines the proposed framework of “dynamic unity” with regard to various theoretical problems within each domain. The particular cognitive science issues discussed in the paper include: (1) the binding problem in the brain; (2) the mental unit of conceptual organization; (3) defining ‘wordhood’ in linguistics; and (4) identifying the unit of cognition in the natural environment.
Physical Review B | 2000
Oron Zachar
For stripes in doped antiferromagnets, we find that the ratio of spin and charge correlation lenghts,
Physica C-superconductivity and Its Applications | 1997
V. J. Emery; Steven A. Kivelson; Oron Zachar
\xi_{s}/\xi_{c}
Physical Review B | 2002
Oron Zachar
, provide a sharp criterion for determining the dominant form of disorder in the system. If stripes disorder is controlled by topological defects then
Physical Review B | 1997
V. J. Emery; Steven A. Kivelson; Oron Zachar
\xi_{s}/\xi_{c}\lesssim 1
Archive | 2008
Leonid P. Pryadko; Steven A. Kivelson; Oron Zachar
. In contast, if stripes correlations are disordered primarily by non-topological elastic deformations (i.e., a Bragg-Glass type of disorder) then