c-axis Raman Scattering in MgB2: Observation of a Dirty-Limit Gap in the pi-bands

Raman scattering spectra from the ac-face of thick MgB2 single crystals were measured in zz, xz and xx polarisations. In zz and xz polarisations a threshold at around 29 cm^{-1} forms in the below Tc continuum but no pair-breaking peak is seen, in contrast to the sharp pair-breaking peak at around 100 cm^{-1} seen in xx polarisation. The zz and xz spectra are consistent with Raman scattering from a dirty superconductor while the sharp peak in the xx spectra argues for a clean system. Analysis of the spectra resolves this contradiction, placing the larger and smaller gap magnitudes in the sigma and pi bands, and indicating that relatively strong impurity scattering is restricted to the pi bands.Comment: Revised manuscript accepted for publication in Physical Review Letter

Dynamical Screening and Superconducting State in Intercalated Layered Metallochloronitrides

An essential property of layered systems is the dynamical nature of the screened Coulomb interaction. Low energy collective modes appear as a consequence of the layering and provide for a superconducting-pairing channel in addition to the electron-phonon induced attractive interaction. We show that taking into account this feature allows to explain the high critical temperatures (Tc~26K) observed in recently discovered intercalated metallochloronitrides. The exchange of acoustic plasmons between carriers leads to a significant enhancement of the superconducting critical temperature that is in agreement with the experimental observations

Enhancement of soft x-ray emission using prepulses with 2ω and 4ω laser plasmas

Copyright 1988 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics, 63(5), 1787-1789, 1988 and may be found at http://dx.doi.org/10.1063/1.33992

Supersymmetric Modified Korteweg-de Vries Equation: Bilinear Approach

A proper bilinear form is proposed for the N=1 supersymmetric modified Korteweg-de Vries equation. The bilinear B\"{a}cklund transformation of this system is constructed. As applications, some solutions are presented for it.Comment: 8 pages, LaTeX using packages amsmath and amssymb, some corrections mad

Gauge-boson propagator in out of equilibrium quantum-field system and the Boltzmann equation

We construct from first principles a perturbative framework for studying nonequilibrium quantum-field systems that include gauge bosons. The system of our concern is quasiuniform system near equilibrium or nonequilibrium quasistationary system. We employ the closed-time-path formalism and use the so-called gradient approximation. No further approximation is introduced. We construct a gauge-boson propagator, with which a well-defined perturbative framework is formulated. In the course of construction of the framework, we obtain the generalized Boltzmann equation (GBE) that describes the evolution of the number-density functions of gauge-bosonic quasiparticles. The framework allows us to compute the reaction rate for any process taking place in the system. Various processes, in turn, cause an evolution of the systems, which is described by the GBE.Comment: 28 page

Glasslike vs. crystalline thermal conductivity in carrier-tuned Ba8Ga16X30 clathrates (X = Ge, Sn)

The present controversy over the origin of glasslike thermal conductivity observed in certain crystalline materials is addressed by studies on single-crystal x-ray diffraction, thermal conductivity k(T) and specific heat Cp(T) of carrier-tuned Ba8Ga16X30 (X = Ge, Sn) clathrates. These crystals show radically different low-temperature k(T) behaviors depending on whether their charge carriers are electrons or holes, displaying the usual crystalline peak in the former case and an anomalous glasslike plateau in the latter. In contrast, Cp(T) above 4 K and the general structural properties are essentially insensitive to carrier tuning. We analyze these combined results within the framework of a Tunneling/Resonant/Rayleigh scatterings model, and conclude that the evolution from crystalline to glasslike k(T) is accompanied by an increase both in the effective density of tunnelling states and in the resonant scattering level, while neither one of these contributions can solely account for the observed changes in the full temperature range. This suggests that the most relevant factor which determines crystalline or glasslike behavior is the coupling strength between the guest vibrational modes and the frameworks with different charge carriers.Comment: 8 pages, 4 figures, 4 tables, submitted to Phys. Rev.

Energy transport in aluminum targets irradiated by a 263-nm laser

Copyright 1988 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters, 52(10), 786-788, 1988 and may be found at http://dx.doi.org/10.1063/1.9928

Experimental study of energy transport in thin Al and Au foils irradiated with a 263-nm laser

Copyright 1989 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics, 65(12), 5068-5071, 1989 and may be found at http://dx.doi.org/10.1063/1.34318