Superfluid Suppression in d-Wave Superconductors due to Disordered Magnetism

The influence of static magnetic correlations on the temperature-dependent superfluid density \rho_s(T) is calculated for d-wave superconductors. In self-consistent calculations, itinerant holes form incommensurate spin density waves (SDW) which coexist with superconductivity. In the clean limit, the density of states is gapped, and \rho_s(T << T_c) is exponentially activated. In inhomogeneously-doped cases, the SDW are disordered and both the density of states and \rho_s(T) obtain forms indistinguishable from those in dirty but pure d-wave superconductors, in accordance with experiments. We conclude that the observed collapse of \rho_s at x\approx 0.35 in underdoped YBCO may plausibly be attributed to the coexistence of SDW and superconductivity.Comment: 6 pages, 5 figures. Expanded discussio

Role of CuO chains in vortex core structure in YBa2Cu3O{7-delta}

The Bogoliubov-deGennes equations are solved for a proximity model for YBa_2Cu_3O_{7-\delta} in a magnetic field. The model explicitly includes the effects of the one-dimensional CuO chains, whose influence on the vortex core structure is studied. The rapid vortex core contraction as a function of field which is seen experimentally at low magnetic fields is naturally explained by the presence of the chains.Comment: 9 pages, 5 figure

The c axis optical conductivity of layered systems in the superconducting state

In this paper, we discuss the c axis optical conductivity Re [sigma_c(omega)] in the high T_c superconductors, in the superconducting state. The basic premise of this work is that electrons travelling along the c axis between adjacent CuO_2 layers must pass through several intervening layers. In earlier work we found that, for weak inter-layer coupling, it is preferable for electrons to travel along the c axis by making a series of interband transitions rather than to stay within a single (and very narrow) band. Moreover, we found that many of the properties of the normal state optical conductivity, including the pseudogap could be explained by interband transitions. In this work we examine the effect of superconductivity on the interband conductivity. We find that, while the onset of superconductivity is clearly evident in the spectrum, there is no clear signature of the symmetry of the superconducting order parameter.Comment: 6 pages, 4 figure

Many-Impurity Effects in Fourier Transform Scanning Tunneling Spectroscopy

Fourier transform scanning tunneling spectroscopy (FTSTS) is a useful technique for extracting details of the momentum-resolved electronic band structure from inhomogeneities in the local density of states due to disorder-related quasiparticle scattering. To a large extent, current understanding of FTSTS is based on models of Friedel oscillations near isolated impurities. Here, a framework for understanding many-impurity effects is developed based on a systematic treatment of the variance Delta rho^2(q,omega) of the Fourier transformed local density of states rho(q,\omega). One important consequence of this work is a demonstration that the poor signal-to-noise ratio inherent in rho(q,omega) due to randomness in impurity positions can be eliminated by configuration averaging Delta rho^2(q,omega). Furthermore, we develop a diagrammatic perturbation theory for Delta rho^2(q,omega) and show that an important bulk quantity, the mean-free-path, can be extracted from FTSTS experiments.Comment: 7 pages, 5 figures. A version of the paper with high resolution, colour figures is available at http://www.trentu.ca/physics/batkinson/FTSTS.ps.gz minor revisions in response to refree report + figure 5 is modifie

Marked expansion of exocrine and endocrine pancreas with incretin therapy in humans with increased exocrine pancreas dysplasia and the potential for glucagon-producing neuroendocrine tumors.

Controversy exists regarding the potential regenerative influences of incretin therapy on pancreatic β-cells versus possible adverse pancreatic proliferative effects. Examination of pancreata from age-matched organ donors with type 2 diabetes mellitus (DM) treated by incretin therapy (n = 8) or other therapy (n = 12) and nondiabetic control subjects (n = 14) reveals an ∼40% increased pancreatic mass in DM treated with incretin therapy, with both increased exocrine cell proliferation (P &lt; 0.0001) and dysplasia (increased pancreatic intraepithelial neoplasia, P &lt; 0.01). Pancreata in DM treated with incretin therapy were notable for α-cell hyperplasia and glucagon-expressing microadenomas (3 of 8) and a neuroendocrine tumor. β-Cell mass was reduced by ∼60% in those with DM, yet a sixfold increase was observed in incretin-treated subjects, although DM persisted. Endocrine cells costaining for insulin and glucagon were increased in DM compared with non-DM control subjects (P &lt; 0.05) and markedly further increased by incretin therapy (P &lt; 0.05). In conclusion, incretin therapy in humans resulted in a marked expansion of the exocrine and endocrine pancreatic compartments, the former being accompanied by increased proliferation and dysplasia and the latter by α-cell hyperplasia with the potential for evolution into neuroendocrine tumors

The impact of asking intention or self-prediction questions on subsequent behavior: a meta-analysis

The current meta-analysis estimated the magnitude of the impact of asking intention and self-prediction questions on rates of subsequent behavior, and examined mediators and moderators of this question–behavior effect (QBE). Random-effects meta-analysis on 116 published tests of the effect indicated that intention/prediction questions have a small positive effect on behavior (d+ = 0.24). Little support was observed for attitude accessibility, cognitive dissonance, behavioral simulation, or processing fluency explanations of the QBE. Multivariate analyses indicated significant effects of social desirability of behavior/behavior domain (larger effects for more desirable and less risky behaviors), difficulty of behavior (larger effects for easy-to-perform behaviors), and sample type (larger effects among student samples). Although this review controls for co-occurrence of moderators in multivariate analyses, future primary research should systematically vary moderators in fully factorial designs. Further primary research is also needed to unravel the mechanisms underlying different variants of the QBE

A spectral method for elliptic equations: the Dirichlet problem

An elliptic partial differential equation Lu=f with a zero Dirichlet boundary condition is converted to an equivalent elliptic equation on the unit ball. A spectral Galerkin method is applied to the reformulated problem, using multivariate polynomials as the approximants. For a smooth boundary and smooth problem parameter functions, the method is proven to converge faster than any power of 1/n with n the degree of the approximate Galerkin solution. Examples in two and three variables are given as numerical illustrations. Empirically, the condition number of the associated linear system increases like O(N), with N the order of the linear system.Comment: This is latex with the standard article style, produced using Scientific Workplace in a portable format. The paper is 22 pages in length with 8 figure

Effect of Proximity Coupling of Chains and Planes on the Penetration Depth Anisotropy in Y_1Ba_2Cu_3O_7

We calculate the penetration depth $\lambda$ in the $a$, $b$ and $c$ directions for a simple model of YBa$_2$Cu$_3$O$_7$. In this model there are two layers---representing a CuO$_2$ plane and a CuO chain---per unit cell. There is a BCS--like pairing (both $s$ wave and $d$ wave are considered) interaction localised in the CuO$_2$ planes. The CuO chains become superconducting at temperatures lower than $T_c$ because of their proximity to the planes, and there is an induced gap in the chains. Since the temperature dependence of the penetration depth in the $b$ direction (along the chains) is sensitive to the size of the induced gap, the difference between the shapes of the penetration depth curves in the $a$ and $b$ directions reveals a great deal about the nature of the condensate in the chains. We find that in our proximity model there are always regions of the chain Fermi surface on which the induced gap is much smaller than $T_c$, so that the temperature dependence of $\lambda_b$ is always different than that of $\lambda_a$. Experimental observations of the of the $ab$ anisotropy show nearly identical temperature dependences. The main result of our paper, then, is that a simple proximity model in which the pairing interaction is localized to the planes, and the planes are coherently coupled to the chains cannot account for the superfluid on the chains.Comment: 24 Pages, Submitted to Phys. Rev.

A multidimensionally consistent version of Hirota's discrete KdV equation

A multidimensionally consistent generalisation of Hirota's discrete KdV equation is proposed, it is a quad equation defined by a polynomial that is quadratic in each variable. Soliton solutions and interpretation of the model as superposition principle are given. It is discussed how an important property of the defining polynomial, a factorisation of discriminants, appears also in the few other known discrete integrable multi-quadratic models.Comment: 11 pages, 2 figure