4D-XY quantum criticality in a doped Mott insulator

A new phenomenology is proposed for the superfluid density of strongly underdoped cuprate superconductors based on recent data for ultra-clean single crystals of YBCO. The data feature a puzzling departure from Uemura scaling and a decline of the slope as the T_c = 0 quantum critical point is approached. We show that this behavior can be understood in terms of the renormalization of quasiparticle effective charge by quantum fluctuations of the superconducting phase as described by a (3+1)-dimensional XY model. We calculate the renormalization of the superfluid density and its slope, explain the new phenomenology, and predict its eventual demise close to the QCP.Comment: Version published in PRL. For additional info and related work visit http://www.physics.ubc.ca/~fran

Exact summation of vertex corrections to the penetration depth in d-wave superconductors

A variety of experiments suggest that in the cuprates, the low-energy superconducting quasiparticles undergo forward scattering from extended impurity potentials. We argue that when such potentials dominate the scattering, the penetration depth may be computed in a simple zero-angle scattering approximation (ZSA), in which the vertex corrections to the Meissner effect may be summed exactly. We find a remarkably simple relationship between the normal fluid density and the quasiparticle density of states of the disordered system which holds for every realization of the disorder. We expect this result to be relevant to the $ab$-plane penetration depth in high-purity single crystals of underdoped YBCO.Comment: 4 pages, submitted to PR

Reliable and robust molecular sexing of the hen harrier (Circus cyaneus) using PCR-RFLP of the CHD1 gene

The hen harrier (Circus cyaneus) is a bird of prey that is persecuted in the United Kingdom, and there is a need for a DNA-based individual identification and sexing system for the use in forensic investigations. This study reports a new set of PCR primers for the chromo-helicase-DNA-binding protein 1 gene, which allows sexing using PCR-RFLP. Instead of exonic primers that amplify across a large intron, this set consists of a primer within the intron, enabling reduction in amplicon sizes from 356 to 212 bp and 565 to 219 bp in W and Z chromosomes. DNA degradation and dilution experiments demonstrate that this set is significantly more robust than one that amplifies across the intron, and sequencing of the intronic primer-binding region across several individuals shows that it is highly conserved. While our objective is to incorporate this primer set into an STR-based individualization kit, it may in the meantime prove useful in forensic or conservation studies

Coherence resonance in an unijunction transistor relaxation oscillator

The phenomenon of coherence resonance (CR) is investigated in an unijunction transistor relaxation oscillator (UJT-RO) and quantified by estimating the normal variance (NV). Depending upon the measuring points two types of NV curves have been obtained. We have observed that the degradations in coherency at higher noise amplitudes in our system is probably the result of direct interference of coherent oscillations and the stochastic perturbation. Degradation of coherency may be minimal if this direct interference of noise and coherent oscillations is eliminated.Comment: 4 pages, Coherence resonace, Uni junction relaxation oscillato