Berezinskii-Kosterlitz-Thouless Transition in Spin-Charge Separated Superconductor

A model for spin-charge separated superconductivity in two dimensions is introduced where the phases of the spinon and holon order parameters couple gauge-invariantly to a statistical gauge-field representing chiral spin-fluctuations. The model is analyzed in the continuum limit and in the low-temperature limit. In both cases we find that physical electronic phase correlations show a superconducting-normal phase transition of the Berezinskii-Kosterlitz-Thouless type, while statistical gauge-field excitations are found to be strictly gapless. The normal-to-superconductor phase boundary for this model is also obtained as a function of carrier density, where we find that its shape compares favorably with that of the experimentally observed phase diagram for the oxide superconductors.Comment: 35 pages, TeX, CSLA-P-93-

Fermion Analogy for Layered Superconducting Films in Parallel Magnetic Field

The equivalence between the Lawrence-Doniach model for films of extreme type-II layered superconductors and a generalization of the back-scattering model for spin-1/2 electrons in one dimension is demonstrated. This fermion analogy is then exploited to obtain an anomalous $H_{\parallel}^{-1}$ tail for the parallel equilibrium magnetization of the minimal double layer case in the limit of high parallel magnetic fields $H_{\parallel}$ for temperatures in the critical regime.Comment: 11 pages of plain TeX, 1 postscript figur

Low ordered magnetic moment by off-diagonal frustration in undoped parent compounds to iron-based high-Tc superconductors

A Heisenberg model over the square lattice recently introduced by Si and Abrahams to describe local-moment magnetism in the new class of Fe-As high-Tc superconductors is analyzed in the classical limit and on a small cluster by exact diagonalization. In the case of spin-1 iron atoms, large enough Heisenberg exchange interactions between neighboring spin-1/2 moments on different iron 3d orbitals that frustrate true magnetic order lead to hidden magnetic order that violates Hund's rule. It accounts for the low ordered magnetic moment observed by elastic neutron diffraction in an undoped parent compound to Fe-As superconductors. We predict that low-energy spin-wave excitations exist at wavenumbers corresponding to either hidden Neel or hidden ferromagnetic order.Comment: 7 pages, 6 figures, version published in Physical Review Letter

Collective pinning of imperfect vortex lattices by material line defects in extreme type-II superconductors

The critical current density shown by a superconductor at the extreme type-II limit is predicted to follow an inverse square-root power law with external magnetic field if the vortex lattice is weakly pinned by material line defects. It acquires an additional inverse dependence with thickness along the line direction once pinning of the interstitial vortex lines by material point defects is included. Moderate quantitative agreement with the critical current density shown by second-generation wires of high-temperature superconductors in kG magnetic fields is achieved at liquid-nitrogen temperature.Comment: 10 pages, 3 figures, 2 tables. To appear in Physical Review

Thermal properties of gauge-fields common to anyon superconductors and spin-liquids

The thermally driven confinement-deconfinement transition exhibited by lattice quantum electrodynamics in two space dimensions is re-examined in the context of the statistical gauge-fields common to anyon superconductors and to spin-liquids. Particle-hole excitations in both systems are bound by a confining string at temperatures below the transition temperature $T_c$. We argue that $T_c$ coincides with the actual critical temperature for anyon superconductivity. The corresponding specific-heat contribution, however, shows a {\it smooth} peak just below $T_c$ characteristic of certain high-temperature superconductors.Comment: 13 pgs, TeX, to appear in Physical Review B (minor revisions

Population of human ventricular cell models calibrated with in vivo measurements unravels ionic mechanisms of cardiac alternans

Cardiac alternansis an important risk factor in cardiac physiology, and is related to the initiation of many pathophysiological conditions. However, the mechanisms underlying the generation of alternans remain unclear. In this study, we used a population of computational human ventricle models based onthe O’Hara model [1] to explore the effect of 11 key factors experimentally reported to be related to alternans. In vivo experimental datasets coming from patients undergoing cardiac surgery were used in the calibration of our in silico population of models. The calibrated models in the population were divided into two groups (Normal and Alternans) depending on alternans occurrence. Our results showed that there were significant differences in the following 5 ionic currents between the two groups: fast sodium current, sodium calcium exchanger current, sodium potassium pump current, sarcoplasmic reticulum (SR) calcium release flux and SR calcium reuptake flux. Further analysis indicated that fast sodium current and SR calcium uptake were the two most significant currents that contributed to voltage and calcium alternans generation, respectively

Phosphoproteomics data classify hematological cancer cell lines according to tumor type and sensitivity to kinase inhibitors

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Muon diffusion and electronic magnetism in Y2_2Ti2_2O7_7

We report a $\mu$SR study in a Y$_2$Ti$_2$O$_7$ single crystal. We observe slow local field fluctuations at low temperature which become faster as the temperature is increased. Our analysis suggests that muon diffusion is present in this system and becomes small below 40 K and therefore incoherent. A surprisingly strong electronic magnetic signal is observed with features typical for muons thermally diffusing towards magnetic traps below $\approx 100$ K and released from them above this temperature. We attribute the traps to Ti$^{3+}$ defects in the diluted limit. Our observations are highly relevant to the persistent spin dynamics debate on $R_2$Ti$_2$O$_7$ pyrochlores and their crystal quality