Photoacoustic wave propagating from normal into superconductive phases in Pb single crystals

Photoacoustic (PA) wave has been examined in a superconductor of the first kind, Pb single crystal. The PA wave is induced by optical excitation of electronic state and propagates from normal into superconductive phases below T$_{\rm C}$. It is clearly shown by wavelet analysis that the measured PA wave includes two different components. The high-frequency component is MHz-ultrasonic and the relative low-frequency one is induced by thermal wave. The latter is observed in a similar manner irrespective of T$_{\rm C}$. On the other hand, the MHz-frequency component is obviously enhanced below T$_{\rm C}$. The behavior is reproduced by the change of attenuation of longitudinal ultrasonic wave and is consistent with BCS theory.Comment: 5 pages, 5 figures (fig.3 is colored), RevTeX4; the text is modifie

Uq(sl^n)U_q(\hat{sl}_n)-analog of the XXZ chain with a boundary

We study $U_q(\hat{sl}_n)$ analog of the XXZ spin chain with a boundary magnetic field h. We construct explicit bosonic formulas of the vacuum vector and the dual vacuum vector with a boundary magnetic field. We derive integral formulas of the correlation functions.Comment: 24 pages, LaTEX2

Effect of disorder outside the CuO2_{2} planes on TcT_{c} of copper oxide superconductors

The effect of disorder on the superconducting transition temperature $T_{c}$ of cuprate superconductors is examined. Disorder is introduced into the cation sites in the plane adjacent to the CuO$_{2}$ planes of two single-layer systems, Bi$_{2.0}$Sr$_{1.6}$Ln$_{0.4}$CuO$_{6+\delta}$ and La$_{1.85-y}$Nd$_{y}$Sr$_{0.15}$CuO$_{4}$. Disorder is controlled by changing rare earth (Ln) ions with different ionic radius in the former, and by varying the Nd content in the latter with the doped carrier density kept constant. We show that this type of disorder works as weak scatterers in contrast to the in-plane disorder produced by Zn, but remarkably reduces $T_{c}$ suggesting novel effects of disorder on high-$T_{c}$ superconductivity.Comment: 5 pages, 5 figures, to be published in Phys. Rev. Let

R-mode Instability of Slowly Rotating Non-isentropic Relativistic Stars

We investigate properties of $r$-mode instability in slowly rotating relativistic polytropes. Inside the star slow rotation and low frequency formalism that was mainly developed by Kojima is employed to study axial oscillations restored by Coriolis force. At the stellar surface, in order to take account of gravitational radiation reaction effect, we use a near-zone boundary condition instead of the usually imposed boundary condition for asymptotically flat spacetime. Due to the boundary condition, complex frequencies whose imaginary part represents secular instability are obtained for discrete $r$-mode oscillations in some polytropic models. It is found that such discrete $r$-mode solutions can be obtained only for some restricted polytropic models. Basic properties of the solutions are similar to those obtained by imposing the boundary condition for asymptotically flat spacetime. Our results suggest that existence of a continuous part of spectrum cannot be avoided even when its frequency becomes complex due to the emission of gravitational radiation.Comment: 10 pages, 4 figures, accepted for publlication in PR

The R-Mode Oscillations in Relativistic Rotating Stars

The axial mode oscillations are examined for relativistic rotating stars with uniform angular velocity. Using the slow rotation formalism and the Cowling approximation, we have derived the equations governing the r-mode oscillations up to the second order with respect to the rotation. In the lowest order, the allowed range of the frequencies is determined, but corresponding spatial function is arbitrary. The spatial function can be decomposed in non-barotropic region by a set of functions associated with the differential equation of the second-order corrections. The equation however becomes singular in barotropic region, and a single function can be selected to describe the spatial perturbation of the lowest order. The frame dragging effect among the relativistic effects may be significant, as it results in rather broad spectrum of the r-mode frequency unlike in the Newtonian first-order calculation.Comment: 19 pages, 4 figures, AAS LaTeX, Accepted for publication in The Astrophysical Journa

Possible direct method to determine the radius of a star from the spectrum of gravitational wave signals

We computed the spectrum of gravitational waves from a dust disk star of radius R inspiraling into a Kerr black hole of mass M and specific angular momentum a. We found that when R is much larger than the wave length of the quasinormal mode, the spectrum has several peaks and the separation of peaks $\Delta\omega$ is proportional to $R^{-1}$ irrespective of M and a. This suggests that the radius of the star in coalescing binary black hole - star systems may be determined directly from the observed spectrum of gravitational wave. This also suggests that the spectrum of the radiation may give us important information in gravitational wave astronomy as in optical astronomy.Comment: 4 pages with 3 eps figures, revtex.sty, accepted for publication in Phys. Rev. Let