Universal linear relations between susceptibility and Tc in cuprates

We developed an experimental method for measuring the intrinsic susceptibility \chi of powder of cuprate superconductors in the zero field limit using a DC-magnetometer. The method is tested with lead spheres. Using this method we determine \chi for a number of cuprate families as a function of doping. A universal linear (and not proportionality) relation between Tc and \chi is found. We suggest possible explanations for this phenomenon.Comment: Accepted for publication in PR

PSL(n∣n)PSL(n|n) Sigma Model as a Conformal Field Theory

We discuss the sigma model on the $PSL(n|n)$ supergroup manifold. We demonstrate that this theory is exactly conformal. The chiral algebra of this model is given by some extension of the Virasoro algebra, similar to the $W$ algebra of Zamolodchikov. We also show that all group invariant correlation functions are coupling constant independent and can be computed in the free theory. The non invariant correlation functions are highly nontrivial and coupling dependent. At the end we compare two and three-point correlation functions of the $PSL(1,1|2)$ sigma model with the correlation functions in the boundary theory of $AdS_3 \times S^3$ and find a qualitative agreement.Comment: 34 pages, 5 figure

Common energy scale for magnetism and superconductivity in underdoped cuprates: A muon spin resonance investigation of (Ca_xLa_1-x)(Ba_1.752-xLa_0.251-x)Cu₃O_y

We characterize the spontaneous magnetic field, and determine the associated temperature Tg, in the superconducting state of Ca(x)La(1-x)Ba(1.75-x)La(0.25+x)Cu(3)O(y) using zero and longitudinal field MuSR measurements for various values of x and y. Our major findings are: (I) Tg and Tc are controlled by the same energy scale, (II) the phase separation between hole poor and hole rich regions is a microscopic one, and (III) spontaneous magnetic fields appear gradually with no moment size evolution