558 research outputs found
Anisotropic chiral d+id superconductivity in NaxCoO2 yH2O
Since its discovery, the superconducting phase in water-intercalated sodium
cobaltates NaxCoO2 yH2O (x~0.3, y~1.3) has posed fundamental challenges in
terms of experimental investigation and theoretical understanding. By a
combined dynamical mean-field and renormalization group approach, we find an
anisotropic chiral d+id wave state as a consequence of multi-orbital effects,
Fermi surface topology, and magnetic fluctuations. It naturally explains the
singlet property and close-to-nodal gap features of the superconducting phase
as indicated by experiments.Comment: 4 pages plus references, 5 figure
K-cowaist of manifolds with boundary
We extend the K-cowaist inequality to generalized Dirac operators in the
sense of Gromov and Lawson and study applications to manifolds with boundary.Comment: 6 page
Accessing topological superconductivity via a combined STM and renormalization group analysis
The search for topological superconductors has recently become a key issue in
condensed matter physics, because of their possible relevance to provide a
platform for Majorana bound states, non-Abelian statistics, and fault-tolerant
quantum computing. We propose a new scheme which links as directly as possible
the experimental search to a material-based microscopic theory for topological
superconductivity. For this, the analysis of scanning tunneling microscopy,
which typically uses a phenomenological ansatz for the superconductor gap
functions, is elevated to a theory, where a multi-orbital functional
renormalization group analysis allows for an unbiased microscopic determination
of the material-dependent pairing potentials. The combined approach is
highlighted for paradigmatic hexagonal systems, such as doped graphene and
water-intercalated sodium cobaltates, where lattice symmetry and electronic
correlations yield a propensity for a chiral singlet topological superconductor
state. We demonstrate that our microscopic material-oriented procedure is
necessary to uniquely resolve a topological superconductor state.Comment: phenomenological STM predictions and temperature dependence of
conductance as well as references added (28 pages, 8 figures
Boundary conditions for scalar curvature
Based on the Atiyah-Patodi-Singer index formula, we construct an obstruction
to positive scalar curvature metrics with mean convex boundaries on spin
manifolds of infinite K-area. We also characterize the extremal case. Next we
show a general deformation principle for boundary conditions of metrics with
lower scalar curvature bounds. This implies that the relaxation of boundary
conditions often induces weak homotopy equivalences of spaces of such metrics.
This can be used to refine the smoothing of codimension-one singularites a la
Miao and the deformation of boundary conditions a la Brendle-Marques-Neves,
among others. Finally, we construct compact manifolds for which the spaces of
positive scalar curvature metrics with mean convex boundaries have nontrivial
higher homotopy groups.Comment: minor change
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