315 research outputs found
Electronic structure of the muonium center as a shallow donor in ZnO
The electronic structure and the location of muonium centers (Mu) in
single-crystalline ZnO were determined for the first time. Two species of Mu
centers with extremely small hyperfine parameters have been observed below 40
K. Both Mu centers have an axial-symmetric hyperfine structure along with a
[0001] axis, indicating that they are located at the AB_{O,//} and BC_{//}
sites. It is inferred from their small ionization energy (~6 meV and 50 meV)
and hyperfine parameters (~10^{-4} times the vacuum value) that these centers
behave as shallow donors, strongly suggesting that hydrogen is one of the
primary origins of n type conductivity in as-grown ZnO.Comment: 4 pages, 4 figures, submitted to PR
Field-Induced Uniform Antiferromagnetic Order Associated with Superconductivity in PrLaCeCuO
Strong correlation between field-induced antiferromagnetic (AF) order and
superconductivity is demonstrated for an electron-doped cuprate superconductor,
PrLaCeCuO (PLCCO). In addition to the specimen with
(which is close to the AF phase boundary, ), we show that
the one with ( K at zero field) also exhibits the
field-induced AF order with a reduced magnitude of the induced moment. The
uniform muon Knight shift at a low magnetic field ( Oe) indicates
that the AF order is not localized within the cores of flux lines, which is in
a marked contrast with theoretical prediction for hole-doped cuprates. The
presence of anomalous non-diagonal hyperfine coupling between muons and Pr ions
is also demonstrated in detail.Comment: 8 pages, 5 figures, to be published in J. Phys. Soc. Jp
Generic First Order Orientation Transition of Vortex Lattices in Type II Superconductors
First order transition of vortex lattices (VL) observed in various
superconductors with four-fold symmetry is explained microscopically by
quasi-classical Eilenberger theory combined with nonlocal London theory. This
transition is intrinsic in the generic successive VL phase transition due to
either gap or Fermi velocity anisotropies. This is also suggested by the
electronic states around vortices. Ultimate origin of this phenomenon is
attributed to some what hidden frustrations of a spontaneous symmetry broken
hexagonal VL on the underlying four-fold crystalline symmetry.Comment: 4 pages, 5 figures, some typos are correcte
Field-Induced Quasiparticle Excitation in Ca(AlSi): Evidence for unconventional Superconductivity
The temperature () and magnetic field () dependence of the magnetic
penetration depth, , in Ca(AlSi) exhibits
significant deviation from that expected for conventional BCS superconductors.
In particular, it is inferred from a field dependence of () at 2.0 K that the quasiparticle excitation is strongly enhanced by the
Doppler shift. This suggests that the superconducting order parameter in
Ca(AlSi) is characterized by a small energy scale
K originating either from anisotropy or multi-gap
structure.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp
Prominent quasi-particle peak in the photoemission spectrum of the metallic phase of V_2O_3
We present the first observation of a prominent quasi-particle peak in the
photoemission spectrum of the metallic phase of V_2O_3 and report new spectral
calculations that combine the local density approximation with the dynamical
mean-field theory (using quantum Monte Carlo simulations) to show the
development of such a distinct peak with decreasing temperature. The
experimental peak width and weight are significantly larger than in the theory.Comment: 4 pages, 3 figures, supercedes cond-mat/010804
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