Canonical-basis solution of the Hartree-Fock-Bogoliubov equation on three-dimensional Cartesian mesh

A method is presented to obtain the canonical-form solutions of the HFB equation for atomic nuclei with zero-range interactions like the Skyrme force. It is appropriate to describe pairing correlations in the continuum in coordinate-space representations. An improved gradient method is used for faster convergences under constraint of orthogonality between orbitals. To prevent high-lying orbitals to shrink into a spatial point, a repulsive momentum dependent force is introduced, which turns out to unveil the nature of high-lying canonical-basis orbitals. The asymptotic properties at large radius and the relation with quasiparticle states are discussed for the obtained canonical basis.Comment: 23 pages including 17 figures, REVTeX4, revised version, scheduled to appear in Phys. Rev. C, Vol.69, No.

Comment on ''Phase Diagram of La2−x_{2-x}Srx_xCuO4_4 Probed in the Infrared: Imprints of Charge Stripe Excitations''

Recently Lucarelli {\it et al.} have reported\cite{lucarelli} temperature-dependence of the in-plane optical reflectivity of La$_{2-x}$Sr$_x$CuO$_4$ over a wide doping range, focusing on the infrared peaks at 30 cm$^{-1}$ (for $x$=0.12), 250 cm$^{-1}$ and 510 cm$^{-1}$. They interpreted the first peak (30 cm$^{-1}$) as a signature of charge stripe ordering, while the latter two (250 cm$^{-1}$ and 510 cm$^{-1}$) are attributed to the polaronic charge excitations. However, careful readers would notice that the reported spectra are largely different from those so far measured on the same system. As we illustrate below, all these peaks are caused by an uncontrolled leakage of the c-axis reflectivity into the measured spectra.Comment: 1 page, 1 figure, accepted for publication in Phys. Rev. Lett 91 (2003

Propagation of a short laser pulse in a plasma

The propagation of an electromagnetic pulse in a plasma is studied for pulse durations that are comparable to the plasma period. When the carrier frequency of the incident pulse is much higher than the plasma frequency, the pulse propagates without distortion at its group speed. When the carrier frequency is comparable to the plasma frequency, the pulse is distorted and leaves behind it an electromagnetic wake.Comment: 6 pages, 5 figures, REVTeX. To be published in Physical Review E, vol. 56, December 1, 199

Oxygen Phonon Branches in Detwinned YBa2Cu3O7

We report results of inelastic neutron scattering measurements of phonon dispersions on a detwinned sample of YBaCu3O7 and compare them with model calculations. Plane oxygen bond stretching phonon branches disperse steeply downwards from the zone center in both the a and the b direction indicating a strong electron-phonon coupling. Half way to the zone boundary, the phonon peaks become ill-defined but we see no need to invoke unit cell doubling or charge stripe formation: lattice dynamical shell model calculations predict such behavior as a result of branch anticrossings. There were no observable superconductivity-related temperature effects on selected plane oxygen bond stretching modes measured on a twinned sample.Comment: 5 pages, 3 figures, To appear in Journal of Low Temperature Physics (Proceedings of MOS2002; Revised version (1) with many changes throughout the tex

Electric-field-induced lifting of the valley degeneracy in alpha-(BEDT-TTF)_2I_3 Dirac-like Landau levels

The relativistic Landau levels in the layered organic material alpha-(BEDT-TTF)_2I_3 [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene] are sensitive to the tilt of the Dirac cones, which, as in the case of graphene, determine the low-energy electronic properties under appropriate pressure. We show that an applied inplane electric field, which happens to be in competition with the tilt of the cones, lifts the twofold valley degeneracy due to a different level spacing. The scenario may be tested in infrared transmission spectroscopy.Comment: 4 pages, 1 figure; version with minor corrections published in EP

Effect of cation size variance on spin and orbital order in Eu1−x_{1-x}(La0.254_{0.254}Y0.746_{0.746})x_{x}VO3_3

We have investigated the $R$-ion ($R$ = rare earth or Y) size variance effect on spin/orbital order in Eu$_{1-x}$(La$_{0.254}$Y$_{0.746}$)$_{x}$VO$_3$. The size variance disturbs one-dimensional orbital correlation in $C$-type spin/$G$-type orbital ordered states and suppresses this spin/orbital order. In contrast, it stabilizes the other spin/orbital order. The results of neutron and resonant X-ray scattering denote that in the other ordered phase, the spin/orbital patterns are $G$-type/$C$-type, respectively.Comment: 4 pages, 4 figures, accepted to Rapid Communication in Physical Review

Electronic structure of MgB2_2 from angle-resolved photoemission spectroscopy

The first angle-resolved photoemission spectroscopy results from MgB$_2$ single crystals are reported. Close to the $\Gamma$K and $\Gamma$M directions, three distinct dispersions are observed approaching the Fermi energy, as can be assigned to the theoretically predicted $\sigma$ (B $2p_{x,y}$) and $\pi$ (B $2p_z$) bands. In addition, we also observed a small parabolic-like band centered around $\Gamma$, and attributed it to a surface-derived state. Good agreement between our results and the band calculations suggests that the electronic structure of MgB$_2$ is of a conventional nature, thus implying that electron correlations are weak, and may be of little importance to the superconductivity in this system.Comment: Revtex 3 pages, 3 JPEG figures, submitted to Phys. Rev. Let

Dispersion of Magnetic Excitations in Superconducting Optimally Doped YBa_2Cu_3O_6.95

Detailed neutron scattering measurements of YBa_2Cu_3O_6.95 found that the resonance peak and incommensurate magnetic scattering induced by superconductivity represent the same physical phenomenon: two dispersive branches that converge near 41 meV and the in-plane wave-vector q_af=(pi/a, pi/a) to form the resonance peak. One branch has a circular symmetry around q_af and quadratic downward dispersion from ~41 meV to the spin gap of 33+-1meV. The other, of lower intensity, disperses from ~41 meV to at least 55 meV. Our results exclude a quartet of vertical incommensurate rods in q-w space expected from spin waves produced by dynamical charge stripes as an origin of the observed incommensurate scattering in optimally-doped YBCO.Comment: Version 3: Author change. Changes made throughout the text and minor changes in figures, Model parameters slightly changed after a small error in the calculation was discovere