18,651 research outputs found
Reply to Comment "Invalidity of classes of approximate Hall effect calculations."
We reply to the criticism raised by Ao in his Comment (cond-mat/9801180).
Being unable to properly treat the Hall conductivity in a mixed state of
superconductors, Ao is looking for possible mistakes in microscopic and
phenomenological calculations, as well as in the corresponding experiments. The
errors in his treatment of the problem (cond-mat/9704247) are analized. We
indicate where the approach advocated by him fails to properly account for the
interaction with impurities and other sources of relaxation.Comment: reply to Comment by Ao (cond-mat/9801180) on our paper in PRL, 79,
1377 (1997), revtex file, 1 page, no figure
Magnetic soft modes in the locally distorted triangular antiferromagnet alpha-CaCr2O4
In this paper we explore the phase diagram and excitations of a distorted
triangular lattice antiferromagnet. The unique two-dimensional distortion
considered here is very different from the 'isosceles'-type distortion that has
been extensively investigated. We show that it is able to stabilize a 120{\deg}
spin structure for a large range of exchange interaction values, while new
structures are found for extreme distortions. A physical realization of this
model is \alpha-CaCr2O4 which has 120{\deg} structure but lies very close to
the phase boundary. This is verified by inelastic neutron scattering which
reveals unusual roton-like minima at reciprocal space points different from
those corresponding to the magnetic order.Comment: 5 pages, 3 figures and lots of spin-wave
Magnetism, X-rays, and Accretion Rates in WD 1145+017 and other Polluted White Dwarf Systems
This paper reports circular spectropolarimetry and X-ray observations of
several polluted white dwarfs including WD 1145+017, with the aim to constrain
the behavior of disk material and instantaneous accretion rates in these
evolved planetary systems. Two stars with previously observed Zeeman splitting,
WD 0322-019 and WD 2105-820, are detected above 5 sigma and > 1 kG, while
WD 1145+017, WD 1929+011, and WD 2326+049 yield (null) detections below this
minimum level of confidence. For these latter three stars, high-resolution
spectra and atmospheric modeling are used to obtain limits on magnetic field
strengths via the absence of Zeeman splitting, finding B* < 20 kG based on data
with resolving power R near 40 000. An analytical framework is presented for
bulk Earth composition material falling onto the magnetic polar regions of
white dwarfs, where X-rays and cyclotron radiation may contribute to accretion
luminosity. This analysis is applied to X-ray data for WD 1145+017, WD
1729+371, and WD 2326+049, and the upper bound count rates are modeled with
spectra for a range of plasma kT = 1 - 10 keV in both the magnetic and
non-magnetic accretion regimes. The results for all three stars are consistent
with a typical dusty white dwarf in a steady-state at 1e8 - 1e9 g/s. In
particular, the non-magnetic limits for WD 1145+017 are found to be well below
previous estimates of up to 1e12 g/s, and likely below 1e10 g/s, thus
suggesting the star-disk system may be average in its evolutionary state, and
only special in viewing geometry.Comment: 14 pages, 7 figures, 3 tables; accepted to MNRA
Rotating vortex core: An instrument for detecting the core excitations
Effects of fermionic zero modes (bound states in a vortex core) on the
rotational dynamics of vortices with sponaneously broken axisymmetry are
considered. The results are compared with the Helsinki experiments where the
vortex cores were driven to a fast rotation and torsional oscillations by an
NMR r.f. field (Kondo et al, Phys. Rev. Lett. 67, 81 (1991)). We predict a
resonance NMR absorption on localized states at the external frequency
comparable with the interelevel distance, which is similar to the cyclotron
Landau damping. The resonances can experimentally resolve the localized levels
in vortex cores. For a pure rotation of the core, the effect depends on the
relative signs of the vortex winding number and of the core rotation; thus it
is sensitive to the direction of rotation of the container. The similarity with
the fermionic zero modes on the fundamental strings, which simulate the
thermodynamics of black holes, is discussed.Comment: RevTex file, 7 pages, 1 Figure, extended and clarified after referee
Reports, to appear in Phys. Rev.
Fusion products, Kostka polynomials, and fermionic characters of su(r+1)_k
Using a form factor approach, we define and compute the character of the
fusion product of rectangular representations of \hat{su}(r+1). This character
decomposes into a sum of characters of irreducible representations, but with
q-dependent coefficients. We identify these coefficients as (generalized)
Kostka polynomials. Using this result, we obtain a formula for the characters
of arbitrary integrable highest-weight representations of \hat{su}(r+1) in
terms of the fermionic characters of the rectangular highest weight
representations.Comment: 21 pages; minor changes, typos correcte
An Algebraic Approach to Linear-Optical Schemes for Deterministic Quantum Computing
Linear-Optical Passive (LOP) devices and photon counters are sufficient to
implement universal quantum computation with single photons, and particular
schemes have already been proposed. In this paper we discuss the link between
the algebraic structure of LOP transformations and quantum computing. We first
show how to decompose the Fock space of N optical modes in finite-dimensional
subspaces that are suitable for encoding strings of qubits and invariant under
LOP transformations (these subspaces are related to the spaces of irreducible
unitary representations of U(N)). Next we show how to design in algorithmic
fashion
LOP circuits which implement any quantum circuit deterministically. We also
present some simple examples, such as the circuits implementing a CNOT gate and
a Bell-State Generator/Analyzer.Comment: new version with minor modification
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