Fermi-Liquid Interactions in d-Wave Superconductor

This article develops a quantitative quasiparticle model of the low-temperature properties of d-wave superconductors which incorporates both Fermi-liquid effects and band-structure effects. The Fermi-liquid interaction effects are found to be classifiable into strong and negligible renormalizaton effects, for symmetric and antisymmetric combinations of the energies of $k\uparrow$ and $-k\downarrow$ quasiparticles, respectively. A particularly important conclusion is that the leading clean-limit temperature-dependent correction to the superfluid density is not renormalized by Fermi-liquid interactions, but is subject to a Fermi velocity (or mass) renormalization effect. This leads to difficulties in accounting for the penetration depth measurements with physically acceptable parameters, and hence reopens the question of the quantitative validity of the quasiparticle picture.Comment: 4 page

High Temperature Photochemistry in the Atmosphere of HD189733b

Recent infrared spectroscopy of hot exoplanets is beginning to reveal their atmospheric composition. Deep with in the planetary atmosphere, the composition is controlled by thermochemical equilibrium. Photochemistry becomes important higher in the atmosphere, at levels above ~1 bar. These two chemistries compete between ~1-10 bars in hot Jupiter-like atmospheres, depending on the strength of the eddy mixing and temperature. HD189733b provides an excellent laboratory in which to study the consequences of chemistry of hot atmospheres. The recent spectra of HD189733b and HD209458b contain signatures of CH4, CO2, CO and H2O. Here we identify the primary chemical pathways that govern the abundances of CH4, CO2, CO and H2O in the cases of thermochemical equilibrium chemistry, photochemistry, and their combination. Our results suggest that the abundance of these species can be photochemically enhanced above or below the thermochemical equilibrium value, so some caution must be taken when assuming that an atmosphere is in strict thermochemical equilibrium

The Prograde Orbit of Exoplanet TrES-2b

We monitored the Doppler shift of the G0V star TrES-2 throughout a transit of its giant planet. The anomalous Doppler shift due to stellar rotation (the Rossiter-McLaughlin effect) is discernible in the data, with a signal-to-noise ratio of 2.9, even though the star is a slow rotator. By modeling this effect we find that the planet's trajectory across the face of the star is tilted by -9 +/- 12 degrees relative to the projected stellar equator. With 98% confidence, the orbit is prograde.Comment: ApJ, in press [15 pages

Optical properties of the pseudogap state in underdoped cuprates

Recent optical measurements of deeply underdoped cuprates have revealed that a coherent Drude response persists well below the end of the superconducting dome. In addition, no large increase in optical effective mass has been observed, even at dopings as low as 1%. We show that this behavior is consistent with the resonating valence bond spin-liquid model proposed by Yang, Rice, and Zhang. In this model, the overall reduction in optical conductivity in the approach to the Mott insulating state is caused not by an increase in effective mass, but by a Gutzwiller factor, which describes decreased coherence due to correlations, and by a shrinking of the Fermi surface, which decreases the number of available charge carriers. We also show that in this model, the pseudogap does not modify the low-temperature, low-frequency behavior, though the magnitude of the conductivity is greatly reduced by the Gutzwiller factor. Similarly, the profile of the temperature dependence of the microwave conductivity is largely unchanged in shape, but the Gutzwiller factor is essential in understanding the observed difference in magnitude between ortho-I and -II YBa$_2$Cu$_3$O$_y$.Comment: 9 pages, 6 figures, submitted to Eur. Phys. J.

Clinical Indicators of Symptom Dimensions and Cognitive Ability in Schizophrenia

INTRODUCTION: Schizophrenia is a heterogeneous disorder and it is unknown what causes individual variability in symptoms and cognitive ability. OBJECTIVES: To examine the association between nine clinical predictors measurable at the onset of schizophrenia and five phenotype dimensions: positive, negative (diminished expressivity), negative (motivation and pleasure), disorganised symptoms and cognitive ability. METHODS: 852 participants (mean age 49 years old) with a diagnosis of schizophrenia or schizoaffective depression were included from the CardiffCOGS cross-sectional sample. Phenotype dimensions were created using confirmatory factor analysis and a 5-factor model. Associations were tested using linear regression, adjusting for age and sex. A Bonferroni correction was applied for (p<1.1x10(-3)) for multiple testing. RESULTS: Age of onset of psychosis was significantly associated with positive symptoms (β=-0.18, p=4.0 x10(-6)). Lower premorbid IQ was associated with diminished expressivity (β=-0.25, p= 7.0x10(-13)), reduced motivation and pleasure (β=-0.23, p= 4.3x10(-11)), disorganised symptoms (β=-0.14, p= 7.6x10(-5)) and reduced cognition (β=0.54, p= 4.8x10(-77)). Poor premorbid social adjustment held associations with all except positive. Developmental delay was associated with reduced cognition (β=-0.35, p= 4.3x10(-5)). Cannabis use (year before onset), psychosocial stressors (within 6 months), childhood abuse and family history of schizophrenia held no associations. CONCLUSIONS: Clinical indicators measurable at schizophrenia onset are associated with lifetime symptom variability. A younger psychosis onset is associated with more severe positive symptoms, suggesting possible age-targeted management. Pre-established links of lower premorbid IQ with poor premorbid social adjustment and negative symptom severity with cognition are strengthened. Further investigation could potentially improve diagnosis and guide treatment choice for aspects of schizophrenia with poor outcomes. DISCLOSURE: No significant relationships

Twin boundaries in d-wave superconductors

Twin boundaries in orthorhombic d-wave superconductors are investigated numerically using the Bogoliubov-deGennes formalism within the context of an extended Hubbard model. The twin boundaries are represented by tetragonal regions of variable width, with a reduced chemical potential. For sufficiently large twin boundary width and change in chemical potential, an induced s-wave component may break time-reversal symmetry at a low temperature. This temperature, and the magnitude of the complex component, are found to depend strongly on electron density. The results are compared with recent tunneling measurements.Comment: ReVTeX, 4 pages, 4 postscript figure

Discrete-Lattice Model for Surface Bound States and Tunneling in d-Wave Superconductors

Surface bound states in a discrete-lattice model of a $d_{x^2 - y^2}$ cuprate superconductor are shown to be, in general, coherent superpositions of an incoming excitation and more than one outgoing excitation, and a simple graphical construction based on a surface Brillouin zone is developed to describe their nature. In addition, a momentum-dependent lifetime contribution to the width of these bound states as observed in tunneling experiments is derived and elucidated in physical terms.Comment: 4 pages, 1 figure, revte

Hypothesis-driven candidate genes for schizophrenia compared to genome-wide association results

Candidate gene studies have been a key approach to the genetics of schizophrenia. Results of these studies have been confusing and no genes have been unequivocally implicated. The hypothesis-driven candidate gene literature can be appraised via comparison with the results of genome-wide association studies (GWAS)