For the description of the long‐wavelength quantum states of electrons in crystals with topological defects we establish a general framework on the basis of the continuum theory of defects. The ...resulting one‐particle Schrödinger equation lives on a Riemann‐Cartan manifold, representing the distorted crystal, and consists of two parts. All effects due to the topology of the defects are contained in the first part which has a covariant form and describes the purely geometric particle motion. The second part is non‐covariant and derives from deformation‐dependent tunneling rates of the particle which e.g. are responsible for the existence of bound states to edge dislocations.
The screw-dislocation line energy density
E
SD in a vortex lattice (VL) was numerically computed on the basis of the isotropic London approximation. The computation premised that the slip planes are ...spaced
D
SP apart with the Burgers vectors of two adjacent slip planes being antiparallel. The results of the computation give a practical approximate expression for
E
SD. This expression is valid for vortex-lattice-tilt deformations much less than
a
0/
λ, where
a
0 is the vortex-lattice constant and
λ is the London penetration depth. The approximate expression for
E
SD was applied to the Larkin–Ovchinnikov pinning theory, and stability of screw dislocations in a pinned VL was investigated for the case where the ratio 5
λ/
a
0 ranges around the Ginzburg–Landau parameter. Screw dislocations of high densities (
D
SP∼
a
0) are expected to be stable for sufficiently strong pinning, but screw dislocations of low densities (
D
SP≫
a
0) are always merely metastable. These results provided a probable criterion such that no screw dislocations destruct Bragg-glass order. Within a framework of the present theoretical description, screw-dislocation-induced plasticization is not responsible for discrepancy between the Larkin–Ovchinnikov pinning theory and experiments in bulks (three-dimensional vortex systems).
Topological defects in 1D elastic waves Morales, A.; Méndez-Sánchez, R.A.; Flores, J.
Physica. E, Low-dimensional systems & nanostructures,
08/2003, Letnik:
19, Številka:
3
Journal Article
Recenzirano
Odprti dostop
It has been recently shown theoretically that a topological defect in a 1D periodic potential may give rise to
two localized states within the energy gaps. In this work we present an experimental ...realization of this effect for the case of torsional waves in elastic rods. We also show numerically that
three, or even more, localized states can be present if the parameters characterizing the topological defect are suitably varied.
Bound states of topological defects arising at parametric excitation of waves on the surface of a vertically vibrating thin layer of viscous fluid are investigated theoretically and in experiments. ...Stably existing bound states of two topological defects having like charges are observed. The distance between the topological defects is found to depend on supercriticality and on the depth of the liquid layer. Analysis of the phase field of the bound states of topological defects revealed quadrupolar components. An approximate theory has been constructed that allows one to calculate the phase fields of bound states and determine the dependence of the distance between the defects on governing parameters. It is shown that theoretical calculations give a correct explanation of data obtained in the experiments.
We propose a new model for the nature of the nucleation of HCP from BCC helium. The dynamic release of shear at the surface of the BCC–HCP phase boundary, sustains the simultaneous nucleation and ...growth of topological defects in the BCC phase. The topological defects are lines of dynamic shear in the BCC phase. The shear energy gain of this process balances the surface tension, as the growing HCP surface is quickly covered by many defect-loops. We show that this scenario gives better agreement with experiments, which differ with the classical theory of homogeneous nucleation by 6–10 orders of magnitude.
The cosmic microwave background anisotropies produced by active seeds, such as topological defects, have been computed recently for a variety of models by a number of authors. In this paper we show ...how the generic features of the anisotropies caused by active, incoherent, seeds (that is the absence of acoustic peaks at small scales) can be obtained semianalytically, without entering into the model dependent details of their formation, structure and evolution.
We investigate a composite system formed by micrometer-sized silica spheres and a nematic liquid crystal with positive dielectric anisotropy. The surface of the spheres has been treated to obtain ...homeotropic alignment either by grafting molecules of n-Octadecyltrimetoxysilane or by using lecithin.In a glass cell with planar anchoring conditions, we have experimentally observed the dipole and the Saturn-ring configurations. Due to the planar treatment of the glass substrates the particles align and can form chains. We studied the effect of an electric field applied parallel to the direction of the rubbing, in the plane of the cell.
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