6 research outputs found
Nature of the Low Field Transition in the Mixed State of High Temperature Superconductors
We have numerically studied the statics and dynamics of a model
three-dimensional vortex lattice at low magnetic fields. For the statics we use
a frustrated 3D XY model on a stacked triangular lattice. We model the dynamics
as a coupled network of overdamped resistively-shunted Josephson junctions with
Langevin noise. At low fields, there is a weakly first-order phase transition,
at which the vortex lattice melts into a line liquid. Phase coherence parallel
to the field persists until a sharp crossover, conceivably a phase transition,
near which develops at the same temperature as an infinite
vortex tangle. The calculated flux flow resistivity in various geometries near
closely resembles experiment. The local density of field induced
vortices increases sharply near , corresponding to the experimentally
observed magnetization jump. We discuss the nature of a possible transition or
crossover at (B) which is distinct from flux lattice melting.Comment: Updated references. 46 pages including low quality 25 eps figures.
Contact [email protected] or visit
http://www.physics.ohio-state.edu:80/~ryu/ for better figures and additional
movie files from simulations. To be published in Physical Review B1 01Jun9
3D XY and lowest Landau level fluctuations in deoxygenated YBCO thin films
Conductivity measurements reflect vortex solid melting in YBCO films.
Field-independent glass exponents nu_g=1.9 and z_g=4.0 describe the transition
T_g(H) for 0<H<26 T. At low fields, 3D XY exponents nu_{XY}=0.63 and
z_{XY}=1.25 are also observed, with z_{XY} smaller than expected. These compete
with glass scaling according to multicritical theory. A predicted power-law
form of T_g(H) is observed for 0.5T_c<T_g<T_c. For T_g<0.5T_c, 3D XY scaling
fails, but a lowest Landau level analysis becomes possible, obtaining T_{c2}(H)
with positive curvature.Comment: 4 pages, 5 .eps figures, To be published in Phys. Rev. Let
Comparison of wear characteristics of etched-silicon and carbon nanotube atomic-force microscopy probes
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