29,209 research outputs found
Observation of backscattering-immune chiral electromagnetic modes without time reversal breaking
A strategy is proposed to realize robust transport in time reversal invariant
photonic system. Using numerical simulation and microwave experiment, we
demonstrate that a chiral guided mode in the channel of a three-dimensional
dielectric woodpile photonic crystal is immune to the scattering of a square
patch of metal or dielectric inserted to block the channel. The chirality based
robust transport can be realized in nonmagnetic dielectric materials without
any external field.Comment: 16 pages, 5 figure
Induced Ferromagnetism at BiFeO3/YBa2Cu3O7 Interfaces
Transition metal oxides (TMOs) exhibit many emergent phenomena ranging from
high-temperature superconductivity and giant magnetoresistance to magnetism and
ferroelectricity. In addition, when TMOs are interfaced with each other, new
functionalities can arise, which are absent in individual components. Here, we
report results from first-principles calculations on the magnetism at the
BiFeO3/YBa2Cu3O7 interfaces. By comparing the total energy for various magnetic
spin configurations inside BiFeO3, we are able to show that a metallic
ferromagnetism is induced near the interface. We further develop an interface
exchange-coupling model and place the extracted exchange coupling interaction
strengths, from the first-principles calculations, into a resultant generic
phase diagram. Our conclusion of interfacial ferromagnetism is confirmed by the
presence of a hysteresis loop in field-dependent magnetization data. The
emergence of interfacial ferromagnetism should have implications to electronic
and transport properties.Comment: 13 pages, 4 figure
Determination of the superconducting gap in near optimally doped Bi_2Sr_{2-x}La_xCuO_{6+\delta} (x ~ 0.4) from low-temperature specific heat
Low-temperature specific heat of the monolayer high-Tc superconductor
Bi_2Sr_{2-x}La_xCuO_{6+\delta} has been measured close to the optimal doping
point (x ~ 0.4) in different magnetic fields. The identification of both a T^2
term in zero field and a \sqrt{H} dependence of the specific heat in fields is
shown to follow the theoretical prediction for d-wave pairing, which enables us
to extract the slope of the superconducting gap in the vicinity of the nodes
(v_{\Delta}, which is proportional to the superconducting gap \Delta_0 at the
antinodes according to the standard d_{x^2-y^2} gap function). The v_{\Delta}
or \Delta_0 (~ 12 meV) determined from this bulk measurement shows close
agreement with that obtained from spectroscopy or tunneling measurements, which
confirms the simple d-wave form of the superconducting gap.Comment: 5 pages, 4 figures, 1 tabl
Dynamical coupled-channel model of kaon-hyperon interactions
The pi N --> KY and KY --> KY reactions are studied using a dynamical
coupled-channel model of meson-baryon interactions at energies where the baryon
resonances are strongly excited. The channels included are: pi N, K \Lambda,
and K\Sigma. The resonances considered are: N^* [S_{11}(1650), P_{11}(1710),
P_{13}(1720),D_{13}(1700)]; \Delta^* [S_{31}(1900), P_{31}(1910),
P_{33}(1920)]; \Lambda ^* [S_{01}(1670), P_{01}(1810)] \Sigma^* [P_{11}(1660),
D_{13}(1670)]; and K^*(892). The basic non-resonant \pi N --> KY and KY --> KY
transition potentials are derived from effective Lagrangians using a unitary
transformation method. The dynamical coupled-channel equations are simplified
by parametrizing the pi N -->pi N amplitudes in terms of empirical pi N
partial-wave amplitudes and a phenomenological off-shell function. Two models
have been constructed. Model A is built by fixing all coupling constants and
resonance parameters using SU(3) symmetry, the Particle Data Group values, and
results from a constituent quark model. Model B is obtained by allowing most of
the parameters to vary around the values of model A in fitting the data. Good
fits to the available data for pi^- p to K^0 \Lambda, K^0 \Sigma^0 have been
achieved. The investigated kinematics region in the center-of-mass frame goes
from threshold to 2.5 GeV. The constructed models can be imbedded into
associated dynamical coupled-channel studies of kaon photo- and
electro-production reactions.Comment: 35 pages, 11 Figure
Sharp and Smooth Boundaries of Quantum Hall Liquids
We study the transition between sharp and smooth density distributions at the
edges of Quantum Hall Liquids in the presence of interactions. We find that,
for strong confining potentials, the edge of a liquid is described by
the Fermi Liquid theory, even in the presence of interactions, a
consequence of the chiral nature of the system. When the edge confining
potential is decreased beyond a point, the edge undergoes a reconstruction and
electrons start to deposit a distance magnetic lengths away from the
initial QH Liquid. Within the Hartree-Fock approximation, a new pair of
branches of gapless edge excitations is generated after the transition. We show
that the transition is controlled by the balance between a long-ranged
repulsive Hartree term and a short-ranged attractive exchange term. Such
transition also occurs for Quantum Dots in the Quantum Hall Regime, and should
be observable in resonant tunneling experiments. Electron tunneling into the
reconstructed edge is also discussed.Comment: 28 pages, REVTeX 3.0, 18 figures available upon request,
cond-mat/yymmnn
- …