5,217 research outputs found
Excitation hierarchy of the quantum sine-Gordon spin chain in strong magnetic field
The magnetic excitation spectrum of copper pyrimidine dinitrate, a material
containing S=1/2 antiferromagnetic chains with alternating g-tensor and the
Dzyaloshinskii-Moriya interaction, and exhibiting a field-induced spin gap, is
probed using submillimeter wave electron spin resonance spectroscopy. Ten
excitation modes are resolved in the low-temperature spectrum, and their
frequency-field diagram is systematically studied in magnetic fields up to 25
T. The experimental data are sufficiently detailed to make a very accurate
comparison with predictions based on the quantum sine-Gordon field theory.
Signatures of three breather branches and a soliton, as well as those of
several multi-particle excitation modes are identified.Comment: 4 RevTeX pages, 3 figure
Josephson effect in quasi one-dimensional unconventional superconductors
Josephson effect in junctions of quasi one-dimensional triangular lattice
superconductors is discussed, where the theoretical model corresponds to
organic superconductors (TMTSF)_2PF_6. We assume the quarter-filling electron
band and p, d and f wave like pairing symmetries in organic superconductors. To
realize the electronic structures in organic superconductors, we introduce the
asymmetric hopping integral, (t') among second nearest lattice sites. At t'=0,
the Josephson current in the d wave symmetry saturates in low temperatures,
whereas those in the p and the f wave symmetries show the low-temperature
anomaly due to the zero-energy state at the junction interfaces. The
low-temperature anomaly appears even in the d wave symmetry in the presence of
t', whereas the anomaly is suppressed in the f wave symmetry. The shape of the
Fermi surface is an important factor for the formation of the ZES in the
quarter-filling electron systems.Comment: 10 page
Epitaxial growth and magnetic properties of Sr2CrReO6 thin films
The double perovskite Sr2CrReO6 is an interesting material for spintronics,
showing ferrimagnetism up to 635 K with a predicted high spin polarization of
about 86%. We fabricated Sr2CrReO6 epitaxial films by pulsed laser deposition
on (001)-oriented SrTiO3 substrates. Phase-pure films with optimum
crystallographic and magnetic properties were obtained by growing at a
substrate temperature of 700 degree C in pure O2 of 6.6x10-4 mbar. The films
are c-axis oriented, coherently strained, and show less than 20% anti-site
defects. The magnetization curves reveal high saturation magnetization of 0.8
muB per formula unit and high coercivity of 1.1 T, as well as a strong magnetic
anisotropy.Comment: accepted for publicatio
Large-N reduction for N=2 quiver Chern-Simons theories on S^3 and localization in matrix models
We study reduced matrix models obtained by the dimensional reduction of N=2
quiver Chern-Simons theories on S^3 to zero dimension and show that if a
reduced model is expanded around a particular multiple fuzzy sphere background,
it becomes equivalent to the original theory on S^3 in the large-N limit. This
is regarded as a novel large-N reduction on a curved space S^3. We perform the
localization method to the reduced model and compute the free energy and the
vacuum expectation value of a BPS Wilson loop operator. In the large-N limit,
we find an exact agreement between these results and those in the original
theory on S^3.Comment: 46 pages, 11 figures; minor modification
Anomalous time delays and quantum weak measurements in optical micro-resonators
We study inelastic resonant scattering of a Gaussian wave packet with the
parameters close to a zero of the complex scattering coefficient. We
demonstrate, both theoretically and experimentally, that such near-zero
scattering can result in anomalously-large time delays and frequency shifts of
the scattered wave packet. Furthermore, we reveal a close analogy of these
anomalous shifts with the spatial and angular Goos-H\"anchen optical beam
shifts, which are amplified via quantum weak measurements. However, in contrast
to other beam-shift and weak-measurement systems, we deal with a
one-dimensional scalar wave without any intrinsic degrees of freedom. It is the
non-Hermitian nature of the system that produces its rich and non-trivial
behaviour. Our results are generic for any scattering problem, either quantum
or classical. As an example, we consider the transmission of an optical pulse
through a nano-fiber with a side-coupled toroidal micro-resonator. The zero of
the transmission coefficient corresponds to the critical coupling conditions.
Experimental measurements of the time delays near the critical-coupling
parameters verify our weak-measurement theory and demonstrate amplification of
the time delay from the typical inverse resonator linewidth scale to the pulse
duration scale.Comment: 14 pages, 5 figure
Local impedance on a rough surface of a chiral -wave superconductor
We develop a self-consistent approach for calculating the local impedance at
a rough surface of a chiral -wave superconductor. Using the quasiclassical
Eilenberger-Larkin-Ovchinnikov formalism, we numerically find the pair
potential, pairing functions, and the surface density of states taking into
account diffusive electronic scattering at the surface. The obtained solutions
are then employed for studying the local complex conductivity and surface
impedance in the broad range of microwave frequencies (ranging from subgap to
above-gap values). We identify anomalous features of the surface impedance
caused by generation of odd-frequency superconductivity at the surface. The
results are compared with experimental data for SrRuO and provide a
microscopic explanation of the phenomenological two-fluid model suggested
earlier to explain anomalous features of the microwave response in this
material.Comment: 19 pages, 10 figures. Version 2: final version as published in PR
- …