QED3 theory of underdoped high temperature superconductors

Low-energy theory of d-wave quasiparticles coupled to fluctuating vortex loops that describes the loss of phase coherence in a two dimensional d-wave superconductor at T=0 is derived. The theory has the form of 2+1 dimensional quantum electrodynamics (QED3), and is proposed as an effective description of the T=0 superconductor-insulator transition in underdoped cuprates. The coupling constant ("charge") in this theory is proportional to the dual order parameter of the XY model, which is assumed to be describing the quantum fluctuations of the phase of the superconducting order parameter. The principal result is that the destruction of phase coherence in d-wave superconductors typically, and immediately, leads to antiferromagnetism. The transition can be understood in terms of the spontaneous breaking of an approximate "chiral" SU(2) symmetry, which may be discerned at low enough energies in the standard d-wave superconductor. The mechanism of the symmetry breaking is analogous to the dynamical mass generation in the QED3, with the "mass" here being proportional to staggered magnetization. Other insulating phases that break chiral symmetry include the translationally invariant "d+ip" and "d+is" insulators, and various one dimensional charge-density and spin-density waves. The theory offers an explanation for the rounded d-wave-like dispersion seen in ARPES experiments on Ca2CuO2Cl2 (F. Ronning et. al., Science 282, 2067 (1998)).Comment: Revtex, 20 pages, 5 figures; this is a much extended follow-up to the Phys. Rev. Lett. vol.88, 047006 (2002) (cond-mat/0110188); improved presentation, many additional explanations, comments, and references added, sec. IV rewritten. Final version, to appear in Phys. Rev.

Congruence of phenotypic and genetic variation at the subspecific level in a Neotropical passerine

The increasing availability of molecular phylogenies has highlighted the issue that genotypic and phenotypic patterns of variation are not always congruent, particularly below the species level. This has led to an ongoing discussion on the validity of the subspecies category and on the use of molecular data to help revise traditional classifications based on phenotypic data. We compared patterns of spatial diversification in genotype and phenotype in the Blue-black Grosbeak Cyanocompsa cyanoides, a Neotropical songbird with four recognised subspecies. Variation in phenotype and genotype are partially congruent among the four subspecies. The more genetically divergent subspecies C. c. rothschildii is strongly differentiated from the other subspecies in meristic characters, plumage colo uration and song . W e suggest that this taxon be accorded full species status as C. rothschildii. Regarding the remaining diversity within C. cyanoides, both phenotypic and genetic markers suggests that it could be divided into two subgroups, but the boundaries of genetic lineages do not coincide with those of subspecies defined using phenotypic data. Lack of complete congruence between phenotypic and molecular markers may be expected, since they are subject to different evolutionary processes. The discordance could also be due to a methodological problem, as subspecies ? geographic boundaries were defined on the basis of phenotypic descriptions that were not systematically evaluated. We consider the subspecies to be an informative taxonomic entity , but note that many current subspecific designations for diverse species need extensive reassessment.Fil: García, Natalia Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Barreira, Ana Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Lavinia Oblanca, Pablo Damián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Tubaro, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentin