Low lying spectrum of weak-disorder quantum waveguides

We study the low-lying spectrum of the Dirichlet Laplace operator on a randomly wiggled strip. More precisely, our results are formulated in terms of the eigenvalues of finite segment approximations of the infinite waveguide. Under appropriate weak-disorder assumptions we obtain deterministic and probabilistic bounds on the position of the lowest eigenvalue. A Combes-Thomas argument allows us to obtain so-called 'initial length scale decay estimates' at they are used in the proof of spectral localization using the multiscale analysis.Comment: Accepted for publication in Journal of Statistical Physics http://www.springerlink.com/content/0022-471

Synthesis and properties of novel bis(1,3-benzodithiolium)-type dications containing a biaryl unit: New redox systems undergoing reversible structural changes by electron transfer

In order to develop new redox systems which undergo reversible structural changes by electron transfer, bis(1,3-benzodithiolium)-type dications (5 21) containing a biaryl unit have been synthesized by hydride abstraction of the corresponding bis(1,3-benzodithiol-2-yl)biaryis (8). Reduction of 5 2, with zinc gave the corresponding intramolecular cyclization products (6), which reverted to 5(2+) by oxidation. Cyclic voltammetry also showed the efficient interconversion between both states. X-Ray analyses revealed that the twist angle of the biaryl unit decreases largely by reductive intramolecular cyclization.ArticleHETEROCYCLES. 69(1): 365 (2006)journal articl

Electromagnetic response of disordered superconducting cavities

We present the results for the resonant frequency shift and quality factor of disordered niobium (Nb) superconducting radio-frequency cavities driven out of equilibrium by the resonant microwave field. The theory is based on the non-equilibrium theory of superconductivity for the current response to the electromagnetic field at the vacuum–metal interface. We are able to accurately predict the observed frequency shifts with a precision of order fractions of kHz over the full temperature range 0 < T ≤ Tc, including the negative frequency shift anomalies that are observed very near Tc. The origin of these anomalies is shown to be the competition between the normal metal skin depth and the London penetration depth, which diverges as T→Tc−. An analytical approximation to the full current response, valid for |T − Tc|≪ Tc, accounts for the negative frequency shift near Tc. The non-monotonic dependence of the quality factor on the quasiparticle scattering rate is related to the pair-breaking effect of disorder on the superfluid fraction and, thus, the London penetration depth

Observation of New Incommensurate Magnetic Correlations at the Lower Critical Concentration for Superconductivity (x=0.05) in La(2-x)Sr(x)CuO4

Neutron-scattering experiments have been performed on lightly-doped La(2-x)Sr(x)CuO4 single crystals in both the insulating (x=0.03,0.04,0.05) and superconducting (x=0.06) regions. Elastic magnetic peaks are observed at low temperatures in all samples with the maximum peak linewidth occuring at the critical concentration x_c=0.05. New incommensurate peaks are observed only at x=0.05, the positions of which are rotated by 45 degrees in reciprocal space about (pi,pi) from those observed for x>=0.06 in the superconducting phase.Comment: 5 pages, LaTeX, 4 figures include