265 research outputs found
Role of CuO chains in vortex core structure in YBa2Cu3O{7-delta}
The Bogoliubov-deGennes equations are solved for a proximity model for
YBa_2Cu_3O_{7-\delta} in a magnetic field. The model explicitly includes the
effects of the one-dimensional CuO chains, whose influence on the vortex core
structure is studied. The rapid vortex core contraction as a function of field
which is seen experimentally at low magnetic fields is naturally explained by
the presence of the chains.Comment: 9 pages, 5 figure
High-field muSR studies of superconducting and magnetic correlations in cuprates above Tc
The advent of high transverse-field muon spin rotation (TF-muSR) has led to
recent muSR investigations of the magnetic-field response of cuprates above the
superconducting transition temperature T_c. Here the results of such
experiments on hole-doped cuprates are reviewed. Although these investigations
are currently ongoing, it is clear that the effects of high field on the
internal magnetic field distribution of these materials is dependent upon a
competition between superconductivity and magnetism. In La_{2-x}Sr_xCuO_4 the
response to the external field above Tc is dominated by heterogeneous spin
magnetism. However, the magnetism that dominates the observed inhomogeneous
line broadening below x ~ 0.19 is overwhelmed by the emergence of a completely
different kind of magnetism in the heavily overdoped regime. The origin of the
magnetism above x ~ 0.19 is currently unknown, but its presence hints at a
competition between superconductivity and magnetism that is reminiscent of the
underdoped regime. In contrast, the width of the internal field distribution of
underdoped YBa_2Cu_3O_y above Tc is observed to track Tc and the density of
superconducting carriers. This observation suggests that the magnetic response
above Tc is not dominated by electronic moments, but rather inhomogeneous
fluctuating superconductivity.Comment: 28 pages, 11 figures, 104 reference
Evidence for Static Magnetism in the Vortex Cores of Ortho-II YBaCuO
Evidence for static alternating magnetic fields in the vortex cores of
underdoped YBaCuO is reported. Muon spin rotation measurements
of the internal magnetic field distribution of the vortex state of
YBaCuO in applied fields of T and T reveal a
feature in the high-field tail of the field distribution which is not present
in optimally doped YBaCuO and which fits well to a model with
static magnetic fields in the vortex cores. The magnitude of the fields is
estimated to be 18(2) G and decreases above K. We discuss possible
origins of the additional vortex core magnetism within the context of existing
theories.Comment: Submitted to PRL; corresponding author: [email protected]
Abrikosov flux-lines in two-band superconductors with mixed dimensionality
We study vortex structure in a two-band superconductor, in which one band is
ballistic and quasi-two-dimensional (2D), and the other is diffusive and
three-dimensional (3D). A circular cell approximation of the vortex lattice
within the quasiclassical theory of superconductivity is applied to a recently
developed model appropriate for such a two-band system [Tanaka et al 2006 Phys.
Rev. B 73, 220501(R); Tanaka et al 2007 Phys. Rev. B 75, 214512]. We assume
that superconductivity in the 3D diffusive band is "weak", i.e., mostly
induced, as is the case in MgB. Hybridization with the "weak" 3D diffusive
band has significant and intriguing influence on the electronic structure of
the "strong" 2D ballistic band. In particular, the Coulomb repulsion and the
diffusivity in the "weak" band enhance suppression of the order parameter and
enlargement of the vortex core by magnetic field in the "strong" band,
resulting in reduced critical temperature and field. Moreover, increased
diffusivity in the "weak" band can result in an upward curvature of the upper
critical field near the transition temperature. A particularly interesting
feature found in our model is the appearance of additional bound states at the
gap edge in the "strong" ballistic band, which are absent in the single-band
case. Furthermore, coupling with the "weak" diffusive band leads to reduced
band gaps and van Hove singularities of energy bands of the vortex lattice in
the "strong" ballistic band. We find these intriguing features for parameter
values appropriate for MgB.Comment: 11 pages, 14 figure
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