440 research outputs found
Melting of regular and decoupled vortex lattices in BSCCO crystals
The angular dependence of the first-order phase transition (FOT) in the
vortex lattice in BiSrCaCuO crystals was investigated
by a low frequency AC shielding technique (with the AC field ), in
which the static-field component parallel to - () was varied with
the in-plane field held constant. The linear decrease of the
FOT field with increasing ends at a
temperature--dependent critical value of . A new transition,
marked by the abrupt drop of the -plane shielding current, appears at this
point. We draw a new phase diagram with and field
components as coordinates; this features at least two distinct regions in the
vortex solid phase, that are determined by the different interplay between the
pancake vortex-- and Josephson vortex lattice.Comment: 2 pages, 2 figures Paper submitted to the conference proceedings of
M2S-2000 Houston, T
Pre-melting of crossing vortex lattices
The pre-melting of high vortex density planes observed recently in layered
superconductors in tilted magnetic field is explained theoretically. Based on
the structural information of the crossing lattices of pancake and Josephson
vortices the effective vortex cage potential at different lattice sites is
determined numerically. Melting takes place when the thermal energy allows
proliferation of vacancy-interstitial pairs. It is found that the increased
density of pancake vortex stacks in the planes containing Josephson vortices,
rather than their incommensurate structure, is the main cause for pre-melting.Comment: 5 pages, 4 figure
Interplay of Anisotropy and Disorder in the Doping-Dependent Melting and Glass Transitions of Vortices in BiSrCaCuO
We study the oxygen doping dependence of the equilibrium first-order melting
and second-order glass transitions of vortices in
BiSrCaCuO. Doping affects both anisotropy and
disorder. Anisotropy scaling is shown to collapse the melting lines only where
thermal fluctuations are dominant. Yet, in the region where disorder breaks
that scaling, the glass lines are still collapsed. A quantitative fit to
melting and replica symmetry breaking lines of a 2D Ginzburg-Landau model
further reveals that disorder amplitude weakens with doping, but to a lesser
degree than thermal fluctuations, enhancing the relative role of disorder.Comment: 4 pages, 4 figure
Resonant electron-lattice cooling in graphene
Controlling energy flows in solids through switchable electron-lattice
cooling can grant access to a range of interesting and potentially useful
energy transport phenomena. Here we discuss a unique switchable
electron-lattice cooling mechanism arising in graphene due to phonon emission
mediated by resonant scattering on defects in crystal lattice, which displays
interesting analogy to the Purcell effect in optics. This mechanism strongly
enhances the electron-phonon cooling rate, since non-equilibrium carriers in
the presence of momentum recoil due to disorder can access a larger phonon
phase space and emit phonons more effciently. Resonant energy dependence of
phonon emission translates into gate-tunable cooling rates, exhibiting giant
enhancement of cooling occurring when the carrier energy is aligned with the
electron resonance of the defect
Nanomechanics of an individual vortex in an anisotropic type-II superconductor
As shown in recent experiments [Auslaender et al., Nature Physics 5, 35
(2009)] magnetic force microscopy permits one not only to image but also to
manipulate an individual vortex in type-II superconductors, and this
manipulation provides a new powerful tool to study vortex dynamics and pinning.
We derive equations that describe the deformation of an individual vortex in an
anisotropic biaxial type-II superconductor under the action of the microscope's
magnetic tip. These equations take into account the driving force generated by
the tip, the elastic force caused by the vortex deformation, and the pinning
force exerted by point defects. Using these equations, we reproduce the main
features of the experimental data obtained by Auslaender et al.Comment: 11 pages, 13 figure
Investigating The Vortex Melting Phenomenon In BSCCO Crystals Using Magneto-Optical Imaging Technique
Using a novel differential magneto-optical imaging technique we investigate
the phenomenon of vortex lattice melting in crystals of Bi_2Sr_2CaCu_2O_8
(BSCCO). The images of melting reveal complex patterns in the formation and
evolution of the vortex solid-liquid interface with varying field (H) or
temperature (T). We believe that the complex melting patterns are due to a
random distribution of material disorder or inhomogeneities across the sample,
which create fluctuations in the local melting temperature or field value. To
study the fluctuations in the local melting temperature / field, we have
constructed maps of the melting landscape T_m(H,r), viz., the melting
temperature (T_m) at a given location (r) in the sample at a given field (H). A
study of these melting landscapes reveals an unexpected feature: the melting
landscape is not fixed, but changes rather dramatically with varying field and
temperature along the melting line. It is concluded that the changes in both
the scale and shape of the landscape result from the competing contributions of
different types of quenched disorder which have opposite effects on the local
melting transition.Comment: Paper presented at the International Symposium on Advances in
Superconductivity & Magnetism: Materials, Mechanisms & Devices September
25-28, 2001, Mangalore, India. Symposium proceedings will be published in a
special issue of Pramana - Journal of Physic
First order phase transition from the vortex liquid to an amorphous solid
We present a systematic study of the topology of the vortex solid phase in
superconducting BiSrCaCuO samples with low doses of
columnar defects. A new state of vortex matter imposed by the presence of
geometrical contours associated with the random distribution of columns is
found. The results show that the first order liquid-solid transition in this
vortex matter does not require a structural symmetry change.Comment: 4 pages, 5 figure
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