Search results for "Vortex"
showing 10 items of 244 documents
Spectrum of the non-abelian phase in Kitaev's honeycomb lattice model
2008
The spectral properties of Kitaev's honeycomb lattice model are investigated both analytically and numerically with the focus on the non-abelian phase of the model. After summarizing the fermionization technique which maps spins into free Majorana fermions, we evaluate the spectrum of sparse vortex configurations and derive the interaction between two vortices as a function of their separation. We consider the effect vortices can have on the fermionic spectrum as well as on the phase transition between the abelian and non-abelian phases. We explicitly demonstrate the $2^n$-fold ground state degeneracy in the presence of $2n$ well separated vortices and the lifting of the degeneracy due to t…
Phenomenological description of sedimentation in turbulent vortex tangles
2008
The aim of this Brief Report is to provide a simple intuitive derivation of the results for sedimentation velocity of a small spherical particle in a counterflow vortex tangle in turbulent superfluid. When the velocity of the tangle vortex lines is small as compared to that of the particle, our results reduce to those obtained previously by other authors through more complex arguments, except for a logarithmic dependence of one of the coefficients on the vortex line density. Comparison of both derivations may be useful to clarify the range of validity of the expressions for the forces between the particle and the tangle.
Description and evolution of anisotropy in superfluid vortex tangles with counterflow and rotation
2006
We examine several vectorial and tensorial descriptions of the geometry of turbulent vortex tangles. We study the anisotropy in rotating counterflow experiments, in which the geometry of the tangle is especially interesting because of the opposite effects of rotation, which orients the vortices, and counterflow, which randomizes them. We propose to describe the anisotropy and the polarization of the vortex tangle through a tensor, which contains the first and second moments of the distribution of the unit vector ${\mathbf{s}}^{\ensuremath{'}}$ locally tangent to the vortex lines. We use an analogy with paramagnetism to estimate the anisotropy, the average polarization, the polarization fluc…
Waves Propagation in Turbulent Superfluid Helium in Presence of Combined Rotation and Counterflow
2010
A complete study of the propagation of waves (namely longitudinal density and temperature waves, longitudinal and transversal velocity waves and heat waves) in turbulent superfluid helium is made in three situations: a rotating frame, a thermal counterflow, and the simultaneous combination of thermal counterflow and rotation. Our analysis aims to obtain as much as possible information on the tangle of quantized vortices from the wave speed and attenuation factor of these different waves, depending on their relative direction of propagation with respect to the rotation vector.
Singular behavior of a vortex layer in the zero thickness limit
2017
The aim of this paper is to study the Euler dynamics of a 2D periodic layer of non uniform vorticity. We consider the zero thickness limit and we compare the Euler solution with the vortex sheet evolution predicted by the Birkhoff-Rott equation. The well known process of singularity formation in shape of the vortex sheet correlates with the appearance of several complex singularities in the Euler solution with the vortex layer datum. These singularities approach the real axis and are responsible for the roll-up process in the layer motion.
Self-consistent calculation of the flux-flow conductivity in diffusive superconductors
2017
In the framework of Keldysh-Usadel kinetic theory, we study the temperature dependence of flux-flow conductivity (FFC) in diffusive superconductors. By using self-consistent vortex solutions we find the exact values of dimensionless parameters that determine the diffusion-controlled FFC both in the limit of the low temperatures and close to the critical one. Taking into account the electron-phonon scattering we study the transition between flux-flow regimes controlled either by the diffusion or the inelastic relaxation of non-equilibrium quasiparticles. We demonstrate that the inelastic electron-phonon relaxation leads to the strong suppression of FFC as compared to the previous estimates m…
Temperature and magnetic-field dependence of quantum creep in various high-Tcsuperconductors
1999
To investigate the quantum tunneling of almost macroscopic vortex segments we measured the normalized relaxation rate Q of superconducting currents for various high-T{sub c} superconductors (HTS's) down to 100 mK in magnetic fields up to 7 T. At fields below {approx_equal}0.5 T, Q is essentially independent of T in the temperature regime between thermally activated and quantum motion as theoretically expected. However, at higher fields, we find an unexpected linear T dependence of Q persisting down to the lowest temperatures in all investigated samples. Since these compounds were chosen to represent the distinct classes of dirty and clean HTS's, the extrapolated Q(T=0) values are used to di…
Origin of the plateau in the temperature dependence of the normalized magnetization relaxation rate in disordered high-temperature superconductors
2008
The temperature $T$ dependence of the normalized magnetization relaxation rate $S$ in optimally doped ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ films with the external dc magnetic field $H$ oriented along the $c$ axis exhibits the well-known plateau in the intermediate $T$ range, associated with the presence of elastic (collective) vortex creep. The disappearance of the $S(T)$ plateau in the high-$H$ domain $(H\ensuremath{\ge}20\text{ }\text{kOe})$ is not completely understood. We show that in the case of high-temperature superconductors with significant quenched disorder the $S(T)$ plateau is directly related to a crossover in the vortex-creep process…
Guided vortex motion in Nb films on facetted substrate surfaces
2003
Abstract Anisotropy of the pinning force in a superconductor can cause a guiding effect on the vortices, which leads to the appearance of new components in the galvanomagnetic quantities of the sample. In this case one can observe an additional odd magnetoresistive component with respect to magnetic field reversal. Furthermore, an even contribution to the Hall voltage is observed. Guided motion of vortices in Nb films on facetted α-Al2O3 (1 0 1 0) was found by measuring the longitudinal and transversal resistivities of three films with transport current directed parallel, perpendicular and at an angle of 45° with respect to the facet ridges. Field inversion was used to separate the even and…