Residual absorption at zero temperature in d-wave superconductors

In a d-wave superconductor with elastic impurity scattering, not all the available optical spectral weight goes into the condensate at zero temperature, and this leads to residual absorption. We find that for a range of impurity parameters in the intermediate coupling regime between Born (weak) and unitary (strong) limit, significant oscillator strength remains which exhibits a cusp like behavior of the real part of the optical conductivity with upward curvature as a function of frequency, as well as a quasilinear temperature dependence of the superfluid density. The calculations offer an explanation of recent data on ortho-II YBa$_2$Cu$_3$O$_{6.5}$ which has been considered anomalous.Comment: Accepted for publication by Phys. Rev. B 7 Pages and 4 Figure

Is it safe to implant bioresorbable scaffolds in ostial side-branch lesions? Impact of 'neo-carina' formation on main-branch flow pattern. Longitudinal clinical observations

Formation of a 'neo-carina' has been reported after bioresorbable vascular scaffolds (BVS) implantation over side-branches. However, as this 'neo-carina' could protrude into the main-branch, its hemodynamic impact remains unknown. We present two cases of BVS implantation for ostial side-branch lesions, and investigate the flow patterns at follow-up and their potential impact. Computational fluid dynamics analysis was performed, using a 3D mesh created by fusion of 3-dimensional angiogram with optical coherence tomography images. In our first case, mild disturbances were seen when 'neo-carina' did not protrude perpendicularly into the main branch. In the second case, extensive flow re-distribution was observed due to a more pronounced protrusion of the 'neo-carina'. Importantly, these areas of hemodynamic disturbance were observed together with lumen narrowing in a non-stenotic vessel segment. Our case observations highlight the importance of investigating the hemodynamic consequences of BVS implantation in bifurcation lesions and illustrate a novel method to do so invivo

Marginal Fermi liquid analysis of 300 K reflectance of Bi2Sr2CaCu2O8+x

We use 300 K reflectance data to investigate the normal-state electrodynamics of the high temperature superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ over a wide range of doping levels. The data show that at this temperature the free carriers are coupled to a continuous spectrum of fluctuations. Assuming the Marginal Fermi Liquid (MFL) form as a first approximation for the fluctuation spectrum, the doping-dependent coupling constant $\lambda (p)$ can be estimated directly from the slope of the reflectance spectrum. We find that $\lambda (p)$ decreases smoothly with the hole doping level, from underdoped samples with $p=0.103$ ($T_c = 67$ K) where $\lambda (p)= 0.93$ to overdoped samples with $p=0.226$, ($T_c= 60$ K) where $\lambda(p)= 0.53$. An analysis of the intercept and curvature of the reflectance spectrum shows deviations from the MFL spectrum symmetrically placed at the optimal doping point $p=0.16$. The Kubo formula for the conductivity gives a better fit to the experiments with the MFL spectrum up to 2000 cm$^{-1}$ and with an additional Drude component or an additional Lorentz component up to 7000 cm$^{-1}$. By comparing three different model fits we conclude that the MFL channel is necessary for a good fit to the reflectance data. Finally, we note that the monotonic variation of the reflectance slope with doping provides us with an independent measure of the doping level for the Bi-2212 system.Comment: 11 pages, 11 figure

Kinetic Turbulence

The weak collisionality typical of turbulence in many diffuse astrophysical plasmas invalidates an MHD description of the turbulent dynamics, motivating the development of a more comprehensive theory of kinetic turbulence. In particular, a kinetic approach is essential for the investigation of the physical mechanisms responsible for the dissipation of astrophysical turbulence and the resulting heating of the plasma. This chapter reviews the limitations of MHD turbulence theory and explains how kinetic considerations may be incorporated to obtain a kinetic theory for astrophysical plasma turbulence. Key questions about the nature of kinetic turbulence that drive current research efforts are identified. A comprehensive model of the kinetic turbulent cascade is presented, with a detailed discussion of each component of the model and a review of supporting and conflicting theoretical, numerical, and observational evidence.Comment: 31 pages, 3 figures, 99 references, Chapter 6 in A. Lazarian et al. (eds.), Magnetic Fields in Diffuse Media, Astrophysics and Space Science Library 407, Springer-Verlag Berlin Heidelberg (2015

Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors

Quasiclassic Uzadel equations for two-band superconductors in the dirty limit with the account of both intraband and interband scattering by nonmagnetic impurities are derived for any anisotropic Fermi surface. From these equations the Ginzburg-Landau equations, and the critical temperature $T_c$ are obtained. An equation for the upper critical field, which determines both the temperature dependence of $H_{c2}(T)$ and the orientational dependence of $H_{c2}(\theta)$ as a function of the angle $\theta$ between ${\bf H}$ and the c-axis is obtained. It is shown that the shape of the $H_{c2}(T)$ curve essentially depends on the ratio of the intraband electron diffusivities $D_1$ and $D_1$, and can be very different from the standard one-gap dirty limit theory. In particular, the value $H_{c2}(0)$ can considerably exceed $0.7T_cdH_{c2}/dT_c$, which can have important consequences for applications of $MgB_2$. A scaling relation is proposed which enables one to obtain the angular dependence of $H_{c2}(\theta)$ from the equation for $H_{c2}$ at ${\bf H}\| c$. It is shown that, depending on the relation between $D_1$ and $D_2$, the ratio of the upper critical field $H_{c2}^\|/H_{c2}^\perp$ for ${\bf H}\| ab$ and ${\bf H}\perp ab$ can both increase and decrease as the temperature decreases. Implications of the obtained results for $MgB_2$ are discussed

Multiband model for penetration depth in MgB2

The results of first principles calculations of the electronic structure and the electron-phonon interaction in MgB2 are used to study theoretically the temperature dependence and anisotropy of the magnetic field penetration depth. The effects of impurity scattering are essential for a proper description of the experimental results. We compare our results with experimental data and we argue that the two-band model describes the data rather well.Comment: submitted to Phys. Rev.

Mass measurements of neutron-deficient Y, Zr, and Nb isotopes and their impact on rp and νp nucleosynthesis processes

© 2018 The Authors. Published by Elsevier B.V. This manuscript is made available under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence (CC BY-NC-ND 4.0). For further details please see: https://creativecommons.org/licenses/by-nc-nd/4.0/Using isochronous mass spectrometry at the experimental storage ring CSRe in Lanzhou, the masses of 82Zr and 84Nb were measured for the first time with an uncertainty of ∼10 keV, and the masses of 79Y, 81Zr, and 83Nb were re-determined with a higher precision. The latter are significantly less bound than their literature values. Our new and accurate masses remove the irregularities of the mass surface in this region of the nuclear chart. Our results do not support the predicted island of pronounced low α separation energies for neutron-deficient Mo and Tc isotopes, making the formation of Zr–Nb cycle in the rp-process unlikely. The new proton separation energy of 83Nb was determined to be 490(400) keV smaller than that in the Atomic Mass Evaluation 2012. This partly removes the overproduction of the p-nucleus 84Sr relative to the neutron-deficient molybdenum isotopes in the previous νp-process simulations.Peer reviewe

Nonequilibrium phase transitions induced by multiplicative noise: effects of self-correlation

A recently introduced lattice model, describing an extended system which exhibits a reentrant (symmetry-breaking, second-order) noise-induced nonequilibrium phase transition, is studied under the assumption that the multiplicative noise leading to the transition is colored. Within an effective Markovian approximation and a mean-field scheme it is found that when the self-correlation time of the noise is different from zero, the transition is also reentrant with respect to the spatial coupling D. In other words, at variance with what one expects for equilibrium phase transitions, a large enough value of D favors disorder. Moreover, except for a small region in the parameter subspace determined by the noise intensity and D, an increase in the self-correlation time usually preventsthe formation of an ordered state. These effects are supported by numerical simulations.Comment: 15 pages. 9 figures. To appear in Phys.Rev.

Solar Wind Turbulence and the Role of Ion Instabilities

International audienc

Sum rules and energy scales in the high-temperature superconductor YBa2Cu3O6+x

The Ferrell-Glover-Tinkham (FGT) sum rule has been applied to the temperature dependence of the in-plane optical conductivity of optimally-doped YBa_2Cu_3O_{6.95} and underdoped YBa_2Cu_3O_{6.60}. Within the accuracy of the experiment, the sum rule is obeyed in both materials. However, the energy scale \omega_c required to recover the full strength of the superfluid \rho_s in the two materials is dramatically different; \omega_c \simeq 800 cm^{-1} in the optimally doped system (close to twice the maximum of the superconducting gap, 2\Delta_0), but \omega_c \gtrsim 5000 cm^{-1} in the underdoped system. In both materials, the normal-state scattering rate close to the critical temperature is small, \Gamma < 2\Delta_0, so that the materials are not in the dirty limit and the relevant energy scale for \rho_s in a BCS material should be twice the energy gap. The FGT sum rule in the optimally-doped material suggests that the majority of the spectral weight of the condensate comes from energies below 2\Delta_0, which is consistent with a BCS material in which the condensate originates from a Fermi liquid normal state. In the underdoped material the larger energy scale may be a result of the non-Fermi liquid nature of the normal state. The dramatically different energy scales suggest that the nature of the normal state creates specific conditions for observing the different aspects of what is presumably a central mechanism for superconductivity in these materials.Comment: RevTeX 4 file, 9 pages with 7 embedded eps figure