A consistent description of the confining QCD vacuum as a dual superconductor requires a determination of fundamental parameters such as the superconductor correlation length ξ and the field penetration depth λ, which determine whether the superconductor is of type I or type II. We illustrate preliminary results of a lattice determination of ξ for the case of pure Yang-Mills with two colors, ob...

We provide a unified parameter-free explanation of the observed oxygen-isotope effects on the critical temperature, the magnetic-field penetration depth and on the normal-state pseudogap for underdoped cuprate superconductors within the framework of the multi-(bi)polaron theory with strong Coulomb and Fröhlich interactions. We also quantitatively explain the measured critical temperature and th...

The ab-plane reflectance of a Nd 1.85Ce 0.15CuO 4 single crystal (Tc523 K! has been measured from '35 to 9500 cm 21 at temperatures above and below Tc , and the optical properties calculated from a Kramers-Kronig analysis. A rich phonon spectrum is observed, and there are a number of c-axis infrared and Raman modes that are observed at low temperature which are believed to be activated by disor...

We address, within the dual superconductivity model for color confinement, the question whether the Yang-Mills vacuum behaves as a superconductor of type I or type II. In order to do that we compare, for the theory with gauge group SU (2), the determination of the field penetration depth λ with that of the superconductor correlation length ξ. The latter is obtained by measuring the temporal cor...

We use nuclear magnetic resonance (NMR), high-resolution x-ray, and neutron scattering studies to study structural and magnetic phase transitions in phosphorus-doped BaFe2(As(1-x)P(x)2. Previous transport, NMR, specific heat, and magnetic penetration depth measurements have provided compelling evidence for the presence of a quantum critical point (QCP) near optimal superconductivity at x=0.3. H...

Temperature dependence of the London penetration depth λ measured in single crystals of CeCoIn(5) is interpreted as being caused by a strong pair-breaking scattering that makes the superconductivity in this compound gapless. For a gapless d-wave superconductor, we derive λ = λ(0)(1-T(2)/T(c)(2))(-1/2) caused by the combined effect of magnetic and non-magnetic scattering, in excellent agreement ...