9,697 research outputs found
The Most General and Renormalizable Maximal Abelian Gauge
We construct the most general gauge fixing and the associated Faddeev-Popov
ghost term for the SU(2) Yang-Mills theory, which leaves the global U(1) gauge
symmetry intact (i.e., the most general Maximal Abelian gauge). We show that
the most general form involves eleven independent gauge parameters. Then we
require various symmetries which help to reduce the number of independent
parameters for obtaining the simpler form. In the simplest case, the
off-diagonal part of the gauge fixing term obtained in this way is identical to
the modified maximal Abelian gauge term with two gauge parameters which was
proposed in the previous paper from the viewpoint of renormalizability.
In this case, moreover, we calculate the beta function, anomalous dimensions
of all fields and renormalization group functions of all gauge parameters in
perturbation theory to one-loop order. We also discuss the implication of these
results to obtain information on low-energy physics of QCD.Comment: 24 pages, 3 figure
Superconductivity and Spin Fluctuations in the Electron-Doped Infinitely-Layered High Tc Superconductor SrLaCuO (Tc=42K)
This paper describes the first 63-Cu NMR study of an electron-doped
infinitely-layered high Tc superconductor SrLaCuO (Tc=42K). The
spin dynamics in the normal state above Tc exhibits qualitatively the same
behavior as some hole-doped materials with significantly enhanced spin
fluctuations. Below Tc, we observed no signature of a Hebel-Slichter coherence
peak, suggesting an unconventional nature of the symmetry of the
superconducting order parameter.Comment: Invited Paper to SNS-95 Conference (Spectroscopies on Novel
Superconductors 1995 at Stanford). Also presented at Aspen Winter Conference
on Superconductivity and Grenoble M^2S-HTSC in 199
Superconductivity in Pseudo-Binary Silicide SrNixSi2-x with AlB2-Type Structure
We demonstrate the emergence of superconductivity in pseudo-binary silicide
SrNixSi2-x. The compound exhibits a structural phase transition from the cubic
SrSi2-type structure (P4132) to the hexagonal AlB2-type structure (P6/mmm) upon
substituting Ni for Si at approximately x = 0.1. The hexagonal structure is
stabilized in the range of 0.1 < x < 0.7. The superconducting phase appears in
the vicinity of the structural phase boundary. Ni acts as a nonmagnetic dopant,
as confirmed by the Pauli paramagnetic behavior.Comment: 12 pages, 5 figure
Linear Connections and Curvature Tensors in the Geometry of Parallelizable Manifolds
In this paper we discuss curvature tensors in the context of Absolute
Parallelism geometry. Different curvature tensors are expressed in a compact
form in terms of the torsion tensor of the canonical connection. Using the
Bianchi identities some other identities are derived from the expressions
obtained. These identities, in turn, are used to reveal some of the properties
satisfied by an intriguing fourth order tensor which we refer to as Wanas
tensor. A further condition on the canonical connection is imposed, assuming it
is semi-symmetric. The formulae thus obtained, together with other formulae
(Ricci tensors and scalar curvatures of the different connections admitted by
the space) are calculated under this additional assumption. Considering a
specific form of the semi-symmetric connection causes all nonvanishing
curvature tensors to coincide, up to a constant, with the Wanas tensor.
Physical aspects of some of the geometric objects considered are mentioned.Comment: 16 pages LaTeX file, Changed title, Changed content, Added
references, Physical features stresse
Magnetic-field-induced transition in BaVS3
The metal-insulator transition (MIT) of BaVS3 is suppressed under pressure
and above the critical pressure of p~2GPa the metallic phase is stabilized. We
present the results of detailed magnetoresistivity measurements carried out at
pressures near the critical value, in magnetic fields up to B=12T. We found
that slightly below the critical pressure the structural tetramerization --
which drives the MIT -- is combined with the onset of magnetic correlations. If
the zero-field transition temperature is suppressed to a sufficiently low value
(T_MI<15K), the system can be driven into the metallic state by application of
magnetic field. The main effect is not the reduction of T_MI with increasing B,
but rather the broadening of the transition due to the applied magnetic field.
We tentatively ascribe this phenomenon to the influence on the magnetic
structure coupled to the bond-order of the tetramers.Comment: 5 pages, 5 figure
Electrons and phonons in the ternary alloy CaAlSi} as a function of composition
We report a detailed first-principles study of the structural, electronic and
vibrational properties of the superconducting C phase of the ternary
alloy CaAlSi, both in the experimental range ,
for which the alloy has been synthesised, and in the theoretical limits of high
aluminium and high silicon concentration. Our results indicate that, in the
experimental range, the dependence of the electronic bands on composition is
well described by a rigid-band model, which breaks down outside this range.
Such a breakdown, in the (theoretical) limit of high aluminium concentration,
is connected to the appearance of vibrational instabilities, and results in
important differences between CaAl and MgB. Unlike MgB, the
interlayer band and the out-of-plane phonons play a major role on the stability
and superconductivity of CaAlSi and related C intermetallic compounds
NMR Search for the Spin Nematic State in LaFeAsO Single Crystal
We report a 75-As single crystal NMR investigation of LaFeAsO, the parent
phase of a pnictide high Tc superconductor. We demonstrate that spin dynamics
develop a strong two-fold anisotropy within each orthorhombic domain below the
tetragonal-orthorhombic structural phase transition at T[TO]~156 K. This
intermediate state with a dynamical breaking of the rotational symmetry freezes
progressively into a spin density wave (SDW) below T[SDW]~142 K. Our findings
are consistent with the presence of a spin nematic state below T[TO] with an
incipient magnetic order.Comment: Revised manuscript accepted for publication in Phys. Rev. Let
H-Dihyperon in Quark Cluster Model
The H dihyperon (DH) is studied in the framework of the SU(3) chiral quark
model. It is shown that except the chiral field, the overall effect of
the other SU(3) chiral fields is destructive in forming a stable DH. The
resultant mass of DH in a three coupled channel calculation is ranged from 2225
to 2234 .Comment: 9 pages, emte
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