Correlation between TcT_c and anisotropic scattering in Tl2_2Ba2_2CuO6+δ_{6+\delta}

Angle-dependent magnetoresistance measurements are used to determine the isotropic and anisotropic components of the transport scattering rate in overdoped Tl$_2$Ba$_2$CuO$_{6+\delta}$ for a range of $T_c$ values between 15K and 35K. The size of the anisotropic scattering term is found to scale linearly with $T_c$, establishing a link between the superconducting and normal state physics. Comparison with results from angle resolved photoemission spectroscopy indicates that the transport and quasiparticle lifetimes are distinct.Comment: 5 pages, 3 figures, accepted for publication in Physical Review Letter

The role of word frequency and morpho-orthography in agreement processing

Agreement attraction in comprehension (when an ungrammatical verb is read quickly if preceded by a feature-matching local noun) is well described by a cue-based retrieval framework. This suggests a role for lexical retrieval in attraction. To examine this, we manipulated two probabilistic factors known to affect lexical retrieval: local noun word frequency and morpho-orthography (agreement morphology realised with or without –s endings) in a self-paced reading study. Noun number and word frequency affected noun and verb region reading times, with higher-frequency words not eliciting attraction. Morpho-orthography impacted verb processing but not attraction: atypical plurals led to slower verb reading times regardless of verb number. Exploratory individual difference analyses further underscore the importance of lexical retrieval dynamics in sentence processing. This provides evidence that agreement operates via a cue-based retrieval mechanism over lexical representations that vary in their strength and association to number features

Transport properties of the metallic state of overdoped cuprate superconductors from an anisotropic marginal Fermi liquid model

We consider the implications of a phenomenological model self-energy for the charge transport properties of the metallic phase of the overdoped cuprate superconductors. The self-energy is the sum of two terms with characteristic dependencies on temperature, frequency, location on the Fermi surface, and doping. The first term is isotropic over the Fermi surface, independent of doping, and has the frequency and temperature dependence characteristic of a Fermi liquid. The second term is anisotropic over the Fermi surface (vanishing at the same points as the superconducting energy gap), strongly varies with doping (scaling roughly with $T_c$, the superconducting transition temperature), and has the frequency and temperature dependence characteristic of a marginal Fermi liquid. Previously it has been shown this self-energy can describe a range of experimental data including angle-dependent magnetoresistance (ADMR) and quasi-particle renormalisations determined from specific heat, quantum oscillations, and angle-resolved photo-emission spectroscopy (ARPES). Without introducing new parameters and neglecting vertex corrections we show that this model self-energy can give a quantitative description of the temperature and doping dependence of a range of reported transport properties of Tl2201 samples. These include the intra-layer resistivity, the frequency dependent optical conductivity, the intra-layer magnetoresistance, and the Hall coefficient. The temperature dependence of the latter two are particularly sensitive to the anisotropy of the scattering rate and to the shape of the Fermi surface. In contrast, the temperature dependence of the Hall angle is dominated by the Fermi liquid contribution to the self-energy that determines the scattering rate in the nodal regions of the Fermi surface.Comment: 17 pages, 16 figure

Optical response of high-TcT_c cuprates: possible role of scattering rate saturation and in-plane anisotropy

We present a generalized Drude analysis of the in-plane optical conductivity $\sigma_{ab}$($T$,$\omega$) in cuprates taking into account the effects of in-plane anisotropy. A simple ansatz for the scattering rate $\Gamma$($T$,$\omega$), that includes anisotropy, a quadratic frequency dependence and saturation at the Mott-Ioffe-Regel limit, is able to reproduce recent normal state data on an optimally doped cuprate over a wide frequency range. We highlight the potential importance of including anisotropy in the full expression for $\sigma_{ab}$($T$,$\omega$) and challenge previous determinations of $\Gamma$($\omega$) in which anisotropy was neglected and $\Gamma$($\omega$) was indicated to be strictly linear in frequency over a wide frequency range. Possible implications of our findings for understanding thermodynamic properties and self-energy effects in high-$T_c$ cuprates will also be discussed.Comment: 8 pages, 7 figures. To be published in Physical Review

Destruction of chain-superconductivity in YBa_2Cu_4O_8 in a weak magnetic field

We report measurements of the temperature dependent components of the magnetic penetration depth {\lambda}(T) in single crystal samples of YBa_2Cu_4O_8 using a radio frequency tunnel diode oscillator technique. We observe a downturn in {\lambda}(T) at low temperatures for currents flowing along the b and c axes but not along the a axis. The downturn in {\lambda}_b is suppressed by a small dc field of ~0.25 T. This and the zero field anisotropy of {\lambda}(T) likely result from proximity induced superconducting on the CuO chains, however we also discuss the possibility that a significant part of the anisotropy might originate from the CuO2 planes.Comment: 5 page

Application Calling

The motivation for the development of Application Calling grew from an interest in offering a large number of users access to software on an AppleTalk network. The goal of Application Calling was to give access to applications and yet: • limit the disk space requirements • protect software vendors from unauthorized copying of software • maintain the standard Macintosh interface • allow for easy software updates Application Calling does this by using a different method of accessing software. Instead of every user having a copy of an application, every user has a copy of a small file which launches or calls up” the real application. The real applications are then hidden so that they cannot be easily copied. There are, however, two disadvantages to Application Calling: • it can be difficult to implement because the applications must initially be altered using a special application • some applications may not be able to be altered properly The following paper is divided into two major parts. The first part presents ways to use Application Calling, and the second explains the technical points of setting it up