5,341 research outputs found
Nematicity as a route to a magnetic field-induced spin density wave order; application to the high temperature cuprates
The electronic nematic order characterized by broken rotational symmetry has
been suggested to play an important role in the phase diagram of the high
temperature cuprates. We study the interplay between the electronic nematic
order and a spin density wave order in the presence of a magnetic field. We
show that a cooperation of the nematicity and the magnetic field induces a
finite coupling between the spin density wave and spin-triplet staggered flux
orders. As a consequence of such a coupling, the magnon gap decreases as the
magnetic field increases, and it eventually condenses beyond a critical
magnetic field leading to a field-induced spin density wave order. Both
commensurate and incommensurate orders are studied, and the experimental
implications of our findings are discussed.Comment: 5 pages, 3 figure
Collective modes and sound propagation in a p-wave superconductor: SrRuO
There are five distinct collective modes in the recently discovered p-wave
superconductor SrRuO; phase and amplitude modes of the order parameter,
clapping mode (real and imaginary), and spin wave. The first two modes also
exist in the ordinary s-wave superconductors, while the clapping mode with the
energy is unique to SrRuO and couples to the sound
wave. Here we report a theoretical study of the sound propagation in a two
dimensional p-wave superconductor. We identified the clapping mode and study
its effects on the longitudinal and transverse sound velocities in the
superconducting state. In contrast to the case of He, there is no resonance
absorption associated with the collective mode, since in metals , where is the Fermi velocity, {\bf q} is the wave
vector, and is the frequency of the sound wave. However, the velocity
change in the collisionless limit gets modified by the contribution from the
coupling to the clapping mode. We compute this contribution and comment on the
visibility of the effect. In the diffusive limit, the contribution from the
collective mode turns out to be negligible. The behaviors of the sound velocity
change and the attenuation coefficient near in the diffusive limit are
calculated and compared with the existing experimental data wherever it is
possible. We also present the results for the attenuation coefficients in both
of the collisionless and diffusive limits at finite temperatures.Comment: RevTex, 12 pages, 2 figures, Replaced by the published versio
Half quantum vortex in superfluid He-A phase in parallel plate geometry
The half quantum vortex(HQV) in condensate has been studied, since it was
predicted by Salomaa and Volovik in superfluid He-A phase. However, an
experimental evidence for its existence has not been reported so far. Motivated
by a recent experimental report by Yamashita et al\cite{yamashita}, we study
the HQVs in superfluid He confined between two parallel plates with a gap D
10 m in the presence of a magnetic field H 26 mT
perpendicular to the parallel plates. We find that the bound HQVs are more
stable than the singular vortices and free pairs of HQVs, when the rotation
perpendicular to the parallel plates is below the critical speed, 2 rad/s. The bound pair of HQVs accompanies the tilting of -vector out of the plane, which leads to an additional absorption in NMR
spectra. Our study appears to describe the temperature and rotation dependence
of the observed satellite NMR signal, which supports the existence of the HQVs
in He.Comment: 5 pages, 5 figure
Half-quantum vortex and d-soliton in SrRuO
Assuming that the superconductivity in SrRuO is described by a planar
p-wave order parameter, we consider possible topological defects in
SrRuO. In particular, it is shown that both of the -soliton
and half-quantum vortex can be created in the presence of the magnetic field
parallel to the - plane. We discuss how one can detect the -soliton and half-quantum vortex experimentally.Comment: 8 pages, 3 figure
Mechanism of spin-triplet superconductivity in Sr2RuO4
The unique Fermi surfaces and their nesting properties of Sr2RuO4 are
considered. The existence of unconventional superconductivity is shown
microscopically, for the first time, from the magnetic interactions (due to
nesting) and the phonon-mediated interactions. The odd-parity superconductivity
is favored in the and sheets of the Fermi surface, and the
various superconductivities are possible in the sheet. There are a
number of possible odd-parity gaps, which include the gaps with nodes, the
breaking of time-reversal symmetry and .Comment: 4 pages, 3 figure
Degeneracy analysis for a super cell of a photonic crystal and its application to the creation of band gaps
A method is introduced to analyze the degeneracy properties of the band
structure of a photonic crystal making use of the super cells. The band
structure associated with a super cell of a photonic crystal has degeneracies
at the edge of the Brillouin zone if the photonic crystal has some kind of
point group symmetry. Both E-polarization and H-polarization cases have the
same degeneracies for a 2-dimensional (2D) photonic crystal. Two theorems are
given and proved. These degeneracies can be lifted to create photonic band gaps
by changing the transform matrix between the super cell and the smallest unit
cell. The existence of the photonic band gaps for many known 2D photonic
crystals is explained through the degeneracy analysis.Comment: 19 pages, revtex4, 14 figures, p
Fermi liquid near Pomeranchuk quantum criticality
We analyze the behavior of an itinerant Fermi system near a charge
nematic(n=2) Pomeranchuk instability in terms of the Landau Fermi liquid (FL)
theory. The main object of our study is the fully renormalized vertex function
, related to the Landau interaction function. We derive
for a model case of the long-range interaction in the nematic
channel. Already within the Random Phase Approximation (RPA), the vertex is
singular near the instability. The full vertex, obtained by resumming the
ladder series composed of the RPA vertices, differs from the RPA result by a
multiplicative renormalization factor , related to the
single-particle residue and effective mass renormalization . We
employ the Pitaevski-Landau identities, which express the derivatives of the
self-energy in terms of , to obtain and solve a set of coupled
non-linear equations for , , and . We show that near the
transition the system enters a critical FL regime, where and , where is the
charge Landau component which approaches -1 at the instability. We
construct the Landau function of the critical FL and show that all but
Landau components diverge at the critical point. We also show that in
the critical regime the one-loop result for the self-energy is asymptotically exact if one identifies the effective
interaction with the RPA form of .Comment: References added, discussion of the dynamic vertex is modifie
Pairing in the iron arsenides: a functional RG treatment
We study the phase diagram of a microscopic model for the superconducting
iron arsenides by means of a functional renormalization group. Our treatment
establishes a connection between a strongly simplified two-patch model by
Chubukov et al. and a five-band- analysis by Wang et al.. For a wide parameter
range, the dominant pairing instability occurs in the extended s-wave channel.
The results clearly show the relevance of pair scattering between electron and
hole pockets. We also give arguments that the phase transition between the
antiferromagnetic phase for the undoped system and the superconducting phase
may be first order
Dispersion-Independent Terahertz Classification Based on Geometric Algebra for Substance Detection
We demonstrate and validate Geometric Algebra (GA) based terahertz (THz) signal classification of various powders in tablet form of various thicknesses, and compare the results with a conventional Support Vector Machine (SVM) approach. By using geometric algebra we can perform classification independently of dispersion and hence independently of the transmission path length through the sample. In principle, it may be possible to extend the GA coordinate-free transformation to other types of pulsed signals, such as pulsed microwaves or even acoustic signals in such fields as seismology. The classifier is available for download at Github, https://github.com/swuzhousl/Shengling-zhou/blob/geometric-algebra-classifier/GAclassifier
Binary-object spectral-synthesis in 3D (BOSS-3D) -- Modelling H-alpha emission in the enigmatic multiple system LB-1
Context: To quantitatively decode the information stored within an observed
spectrum, detailed modelling of the physical state and accurate radiative
transfer solution schemes are required. In the analysis of stellar spectra, the
numerical model often needs to account for binary companions and 3D structures
in the stellar envelopes. The enigmatic binary (or multiple) system LB-1
constitutes a perfect example of such a complex multi-D problem. Aims: To
improve our understanding of the LB-1 system, we directly modelled the
phase-dependent H-alpha line profiles of this system. To this end, we developed
a multi-purpose binary-object spectral-synthesis code in 3D (BOSS-3D). Methods:
BOSS-3D calculates synthetic line profiles for a given state of the
circumstellar material. The standard pz-geometry commonly used for single stars
is extended by defining individual coordinate systems for each involved object
and by accounting for the appropriate coordinate transformations. The code is
then applied to the LB-1 system, considering two main hypotheses, a binary
containing a stripped star and Be star, or a B star and a black hole with a
disc. Results: Comparing these two scenarios, neither model can reproduce the
detailed phase-dependent shape of the H-alpha line profiles. A satisfactory
match with the observations, however, is obtained by invoking a disc around the
primary object in addition to the Be-star disc or the black-hole accretion
disc. Conclusions: The developed code can be used to model synthetic line
profiles for a wide variety of binary systems, ranging from transit spectra of
planetary atmospheres, to post-asymptotic giant branch binaries including
circumstellar and circumbinary discs and massive-star binaries with stellar
winds and disc systems. For the LB-1 system, our modelling provides strong
evidence that each object in the system contains a disc-like structure
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