Wed' Jan' 25th

1
Evidence for Vortices in the Pseudogap Region of
Y1-xPrxBa2Cu3O7-???from Angular
Magnetoresistivity Measurements
Carmen Almansan Physics Department Kent State
Abstract The high transition temperature
cuprate superconductors represent a new class of
materials, which have extraordinary
superconducting and magnetic properties and great
potential for a wide-range of technological
applications. The most striking relationship
between superconductivity and normal state of the
cuprates is observed in systems with reduced
charge carrier density, i.e., in the so-called
underdoped materials. In this talk, I will show
evidence for flux vortices at temperatures well
above the zero-field superconducting transition
temperature Tc0, in the pseudogap region, from
angular magnetoresistivity measurements on
underdoped Y1-xPrxBa2Cu3O7-d single crystals.
Even though magnetoresistivity is a second order
effect with a very weak signal above Tc0 and with
the dissipative part due to vortex motion even
weaker, angular magnetoresistivity makes it
possible to discriminate between signals coming
from the movement of vortices and of
quasiparticles. Specifically, the angular
dependent in-plane magnetoresistivity of the x gt
0.2 single crystals displays a deviation from the
typical sin2q dependence over a certain
temperature range in the pseudogap region. We
have shown that this deviation is a result of the
presence of a flux-flow type contribution to
magnetoresistivity in this temperature range.
These results are consistent with the existence
of vortex-like excitations in the pseudogap
region that manifest themselves as flux-flow
resistivity, supporting the scenario in which the
zero-field superconducting transition is the
onset of only long-range phase coherence

• Wed. Jan. 25th