7,177 research outputs found
Effect of intraband Coulomb repulsion on the excitonic spin-density wave
We present a study of the magnetic ground state of a two-band model with
nested electron and hole Fermi surfaces and both interband and intraband
Coulomb interactions. Our aim is to understand how the excitonic
spin-density-wave (ESDW) state induced by the interband Coulomb repulsion is
affected by the intraband interactions. We first determine the magnetic
instabilities of our model in an unbiased way by employing the random-phase
approximation (RPA) to calculate the static spin susceptibility in the
paramagnetic state. From this, we construct the mean-field phase diagram,
demonstrating the robustness of the ESDW against the intraband interaction. We
then calculate the RPA transverse spin susceptibility in the ESDW state and
show that the intraband Coulomb repulsion significantly renormalizes the
paramagnon line shape and suppresses the spin-wave velocity. We conclude with a
discussion of the relevance of this suppression for the commensurate ESDW state
of Mn-doped Cr alloys.Comment: 8 pages, 6 figure
Andreev spectroscopy and surface density of states for a three-dimensional time-reversal invariant topological superconductor
A topological superconductor is a fully gapped superconductor that exhibits
exotic zero-energy Andreev surface states at interfaces with a normal metal. In
this paper we investigate the properties of a three-dimensional time reversal
invariant topological superconductor by means of a two-band model with
unconventional pairing in both the inter- and intraband channels. Due to the
bulk-boundary correspondence the presence of Andreev surface states in this
system is directly related to the topological structure of the bulk
wavefunctions, which is characterized by a winding number. Using quasiclassical
scattering theory we construct the spectrum of the Andreev bound states that
appear near the surface and compute the surface density of states for various
surface orientations. Furthermore, we consider the effects of band splitting,
i.e., the breaking of an inversion-type symmetry, and demonstrate that in the
absence of band splitting there is a direct transition between the fully gapped
topologically trivial phase and the nontrivial phase, whereas in the presence
of band splitting there exists a finite region of a gapless nodal
superconducting phase between the fully gapped topologically trivial and
nontrivial phases.Comment: 7 pages, 4 figures, typos corrected, two footnotes adde
Staggered flux vortices and the superconducting transition in the layered cuprates
We propose an effective model for the superconducting transition in the
high-T_c cuprates motivated by the SU(2) gauge theory approach. In addition to
variations of the superconducting phase we allow for local admixture of
staggered flux order. This leads to an unbinding transition of vortices with
staggered flux core that are energetically preferable to conventional vortices.
Based on parameter estimates for the two-dimensional t-J model we argue that
the staggered flux vortices provide a way to understand a phase with a moderate
density of mobile vortices over a large temperature range above T_c that yet
exhibits otherwise normal transport properties. This picture is consistent with
the large Nernst signal observed in this region.Comment: 4 pages, 3 figure
Noise from metallic surfaces -- effects of charge diffusion
Non-local electrodynamic models are developed for describing metallic
surfaces for a diffusive metal. The electric field noise at a distance z_0 from
the surface is evaluated and compared with data from ion chips that show
anomalous heating with a noise power decaying as z_0^{-4}. We find that high
surface diffusion can account for the latter result.Comment: 16 pages, 2 figures. Revised version focusing on charge diffusing and
anomalous heatin
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