1,098 research outputs found
Searching for zeroes: unconventional superconductors in a magnetic field
We review the results of the microscopic approach to the calculation of the
anisotropy in the specific heat in unconventional superconductors under rotated
field. Treating vortex scattering on equal footing with the energy shift we
find that the electronic specific heat may have minima or maxima when the field
is aligned with the nodes, depending on the temperature and field range. We
discuss the influence of the paramagnetic limiting and Fermi surface shape on
the location of the inversion line.Comment: Proceedings of SCES-0
Unconventional superconductors under rotating magnetic field I: density of states and specific heat
We develop a fully microscopic theory for the calculations of the
angle-dependent properties of unconventional superconductors under a rotated
magnetic field. We employ the quasiclassical Eilenberger equations, and use a
variation of the Brandt-Pesch-Tewordt (BPT) method to obtain a closed form
solution for the Green's function. The equations are solved self-consistently
for quasi-two-dimensional () superconductors with the
field rotated in the basal plane. The solution is used to determine the density
of states and the specific heat. We find that applying the field along the gap
nodes may result in minima or maxima in the angle-dependent specific heat,
depending on the location in the T-H plane. This variation is attributed to the
scattering of the quasiparticles on vortices, which depends on both the field
and the quasiparticle energy, and is beyond the reach of the semiclassical
approximation. We investigate the anisotropy across the T-H phase diagram, and
compare our results with the experiments on heavy fermion CeCoIn.Comment: 18 pages, 10 figure
Spectrum of third sound cavity modes on superfluid He films
We report theoretical calculations of the spectrum of third sound modes for a
cylindrically symmetric film of superfluid He, and compare these results
with experimental data for the mode frequencies and amplitude spectrum of
surface waves of superfluid He films.Comment: 8 pages, 5 figures, LaTeX, submitted to JLT
Nodes vs. minima in the energy gap of iron-pnictides from field-induced anisotropy
We develop the formalism for computing the oscillations of the specific heat
and thermal transport under rotated magnetic field in multiband superconductors
with anisotropic gap and apply it to iron-pnictides. We show that these
oscillations change sign at low temperatures and fields, which strongly
influences the conclusions about the gap structure based on experiment. We find
that recent measurements of the specific heat oscillations indicate that the
iron-based superconductors possess an anisotropic gap with deep minima or nodes
close to the line connecting electron and hole pockets. We make predictions for
the behavior of the thermal conductivity that will help distinguish between
these cases.Comment: 4+3 pages, published version with supplemen
Domain Walls in Superfluid 3He-B
We consider domain walls between regions of superfluid 3He-B in which one
component of the order parameter has the opposite sign in the two regions far
from one another. We report calculations of the order parameter profile and the
free energy for two types of domain wall, and discuss how these structures are
relevant to superfluid 3He confined between two surfaces.Comment: 6 pages with 3 figures. Conference proceedings of QSF 2004, Trento,
Ital
Crystalline order in superfluid 3He films
We predict an inhomogeneous phase of superfluid 3He films in which
translational symmetry is spontaneously broken in the plane of the film. This
phase is energetically favored over a range of film thicknesses,
, separating distinct homogeneous superfluid phases.
The instability at the critical film thickness, , is a
single-mode instability generating striped phase order in the film. Numerical
calculations of the order parameter and free energy indicate a second-order
instability to a periodic lattice of degenerate B-like phases separated by
domain walls at . The striped phase should be
identifiable in transport and nuclear magnetic resonance experiments.Comment: 4 pages, 4 figure
Specific heat jump at superconducting transition in the presence of Spin-Density-Wave in iron-pnictides
We analyze the magnitude of the specific heat jump \Delta C at the
superconducting transition temperature T_c in the situation when
superconductivity develops in the pre-existing antiferromagnetic phase. We show
that \Delta C/T_c differs from the BCS value and is peaked at the tri-critical
point where this coexistence phase first emerges. Deeper in the magnetic phase,
the onset of coexistence, T_c, drops and \Delta C/T_c decreases, roughly as
\Delta C/T_c \propto T^2_c at intermediate T_c and exponentially at the lowest
T_c, in agreement with the observed behavior of \Delta C/T_c in iron-based
superconductors.Comment: 4+ pages, 3 figure
Spontaneously broken translational symmetry at edges of high-temperature superconductors: thermodynamics in magnetic field
We investigate equilibrium properties, including structure of the order
parameter, superflow patterns, and thermodynamics of low-temperature surface
phases of layered d_{x^2-y^2}-wave superconductors in magnetic field. At zero
external magnetic field, time-reversal symmetry and continuous translational
symmetry along the edge are broken spontaneously in a second order phase
transition at a temperature , where is the
superconducting transition temperature. At the phase transition there is a jump
in the specific heat that scales with the ratio between the edge length and
layer area as , where is
the jump in the specific heat at the d-wave superconducting transition and
is the superconducting coherence length. The phase with broken symmetry
is characterized by a gauge invariant superfluid momentum that
forms a non-trivial planar vector field with a chain of sources and sinks along
the edges with a period of approximately , and saddle point
disclinations in the interior. To find out the relative importance of
time-reversal and translational symmetry breaking we apply an external field
that breaks time-reversal symmetry explicitly. We find that the phase
transition into the state with the non-trivial vector field keeps
its main signatures, and is still of second order. In the external field, the
saddle point disclinations are pushed towards the edges, and thereby a chain of
edge motifs are formed, where each motif contains a source, a sink, and a
saddle point. Due to a competing paramagnetic response at the edges, the phase
transition temperature is slowly suppressed with increasing magnetic
field strength, but the phase with broken symmetry survives into the mixed
state.Comment: 12 pages, 9 figure
Theory of thermal conductivity in extended- state superconductors: application to ferropnictides
Within a two-band model for the recently discovered ferropnictide materials,
we calculate the thermal conductivity assuming general superconducting states
of ("s-wave") symmetry, considering both currently popular isotropic
"sign-changing" states and states with strong anisotropy, including those
which manifest nodes or deep minima of the order parameter. We consider both
intra- and interband disorder scattering effects, and show that in situations
where a low-temperature linear- exists in the thermal conductivity, it is
not always "universal" as in d-wave superconductors. We discuss the conditions
under which such a term can disappear, as well as how it can be induced by a
magnetic field. We compare our results to several recent experiments.Comment: 13 page
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