5,748 research outputs found

    Stability of Elastic Glass Phases in Random Field XY Magnets and Vortex Lattices in Type II Superconductors

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    A description of a dislocation-free elastic glass phase in terms of domain walls is developed and used as the basis of a renormalization group analysis of the energetics of dislocation loops added to the system. It is found that even after optimizing over possible paths of large dislocation loops, their energy is still very likely to be positive when the dislocation core energy is large. This implies the existence of an equilibrium elastic glass phase in three dimensional random field X-Y magnets, and a dislocation free, bond-orientationally ordered ``Bragg glass'' phase of vortices in dirty Type II superconductors.Comment: 12 pages, Revtex, no figures, submitted to Phys Rev Letter

    Stripes Disorder and Correlation lengths in doped antiferromagnets

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    For stripes in doped antiferromagnets, we find that the ratio of spin and charge correlation lenghts, ξs/ξc\xi_{s}/\xi_{c}, provide a sharp criterion for determining the dominant form of disorder in the system. If stripes disorder is controlled by topological defects then ξs/ξc1\xi_{s}/\xi_{c}\lesssim 1. In contast, if stripes correlations are disordered primarily by non-topological elastic deformations (i.e., a Bragg-Glass type of disorder) then 1<ξs/ξc41<\xi _{s}/\xi_{c}\lesssim 4 is expected. Therefore, the observation of ξs/ξc4\xi _{s}/\xi_{c}\approx 4 in (LaNd)2xSrxCuO4(LaNd)_{2-x}Sr_{x}CuO_{4} and ξs/ξc3\xi_{s}/\xi _{c}\approx 3 in La2/3Sr1/3NiO4La_{2/3}Sr_{1/3}NiO_{4} invariably implies that the stripes are in a Bragg glass type state, and topological defects are much less relevant than commonly assumed. Expected spectral properties are discussed. Thus, we establish the basis for any theoretical analysis of the experimentally obsereved glassy state in these material.Comment: 4 pages, 2 figure

    Goldstone-type fluctuations and their implications for the amorphous solid state

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    In sufficiently high spatial dimensions, the formation of the amorphous (i.e. random) solid state of matter, e.g., upon sufficent crosslinking of a macromolecular fluid, involves particle localization and, concommitantly, the spontaneous breakdown of the (global, continuous) symmetry of translations. Correspondingly, the state supports Goldstone-type low energy, long wave-length fluctuations, the structure and implications of which are identified and explored from the perspective of an appropriate replica field theory. In terms of this replica perspective, the lost symmetry is that of relative translations of the replicas; common translations remain as intact symmetries, reflecting the statistical homogeneity of the amorphous solid state. What emerges is a picture of the Goldstone-type fluctuations of the amorphous solid state as shear deformations of an elastic medium, along with a derivation of the shear modulus and the elastic free energy of the state. The consequences of these fluctuations -- which dominate deep inside the amorphous solid state -- for the order parameter of the amorphous solid state are ascertained and interpreted in terms of their impact on the statistical distribution of localization lengths, a central diagnostic of the the state. The correlations of these order parameter fluctuations are also determined, and are shown to contain information concerning further diagnostics of the amorphous solid state, such as spatial correlations in the statistics of the localization characteristics. Special attention is paid to the properties of the amorphous solid state in two spatial dimensions, for which it is shown that Goldstone-type fluctuations destroy particle localization, the order parameter is driven to zero, and power-law order-parameter correlations hold.Comment: 20 pages, 3 figure

    Deformation of lyotropic chromonic liquid crystal induced by cylindrical surface

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    Department of PhysicsInterfaces, where liquid crystals (LCs) is in contact with other materials, play a pivotal role in most LCbased applications such as displays and sensors. Physicochemical properties of interfaces impose a surface anchoring, and the geometry and topology of confining interfaces determine LC???s director configuration and defects. To our interest, the concavely curved interface with anisotropic curvatures gives rise to a so-called surface-elasticity phenomenon. In this work, we report the director configuration around a cylindrical object embedded in nematic Sunset Yellow (SSY), a representative lyotropic chromonic LC with the large K24 modulus. The nematic SSY is sandwiched between two flat substrates, and a cylinder is placed in the SSY. The flat boundaries induce a homogeneous director field orthogonal to the cylinder???s axis, whereas the cylinder aligns neighboring directors parallel to its axis, based on the theory related with K24. These boundary conditions result in the twist deformation near the cylinder, and we investigate the deformation experimentally and theoretically, and evaluate K24 of SSY.clos

    Equation of state for polymer liquid crystals: theory and experiment

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    The first part of this paper develops a theory for the free energy of lyotropic polymer nematic liquid crystals. We use a continuum model with macroscopic elastic moduli for a polymer nematic phase. By evaluating the partition function, considering only harmonic fluctuations, we derive an expression for the free energy of the system. We find that the configurational entropic part of the free energy enhances the effective repulsive interactions between the chains. This configurational contribution goes as the fourth root of the direct interactions. Enhancement originates from the coupling between bending fluctuations and the compressibility of the nematic array normal to the average director. In the second part of the paper we use osmotic stress to measure the equation of state for DNA liquid crystals in 0.1M to 1M NaCl solutions. These measurements cover 5 orders of magnitude in DNA osmotic pressure. At high osmotic pressures the equation of state, dominated by exponentially decaying hydration repulsion, is independent of the ionic strength. At lower pressures the equation of state is dominated by fluctuation enhanced electrostatic double layer repulsion. The measured equation of state for DNA fits well with our theory for all salt concentrations. We are able to extract the strength of the direct electrostatic double layer repulsion. This is a new and alternative way of measuring effective charge densities along semiflexible polyelectrolytes.Comment: text + 5 figures. Submitted to PR
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