Magnetic Field Dependent Behavior of the CDW ground state in Per2M(mnt)2 (M = Au, Pt)

The Per2M(mnt)2 class of organic conductors exhibit a charge density wave (CDW) ground state below about 12 K, which may be suppressed in magnetic fields of order 20 to 30 T. However, for both cases of counter ion M(mnt)2 species studied (M = Au (zero spin) and M = Pt (spin 1/2)), new high field ground states evolve for further increases in magnetic field. We report recent investigations where thermopower, Hall effect, high pressure and additional transport measurements have been carried out to explore these new high field phases.Comment: 6 pages, 10 figures, 27 reference

Role of anion size, magnetic moment, and disorder on the properties of the organic conductor kappa-(BETS)_2Ga_{1-x}Fe_{x}Cl_{4-y}_Br_{y}

Shubnikov-de Haas and angular dependent magnetoresistance oscillations have been used to explore the role of anion size, magnetic moment, and disorder in the organic conductors kappa-(BETS)_2GaBr_{4} and kappa-(BETS)_2FeCl_{2}_Br_{2} in the isomorphic class kappa-(BETS)_2Ga_{1-x}Fe_{x}Cl_{4-y}_Br_{y}. The results, combined with previous work, show correlations between the anion composition (Ga_{1-x}Fe_{x}Cl_{4-y}_Br_{y}) and the superconducting transition temperature, effective mass, Fermi surface topology, and the mean free path.Comment: 5 pages, 6 figure

The High Magnetic Field Phase Diagram of a Quasi-One Dimensional Metal

We present a unique high magnetic field phase of the quasi-one dimensional organic conductor (TMTSF)$_2$ClO$_4$. This phase, termed "Q-ClO$_4$", is obtained by rapid thermal quenching to avoid ordering of the ClO$_4$ anion. The magnetic field dependent phase of Q-ClO$_4$ is distinctly different from that in the extensively studied annealed material. Q-ClO$_4$ exhibits a spin density wave (SDW) transition at $\approx$ 5 K which is strongly magnetic field dependent. This dependence is well described by the theoretical treatment of Bjelis and Maki. We show that Q-ClO$_4$ provides a new B-T phase diagram in the hierarchy of low-dimensional organic metals (one-dimensional towards two-dimensional), and describe the temperature dependence of the of the quantum oscillations observed in the SDW phase.Comment: 10 pages, 4 figures, preprin

Magnetothemopower study of quasi two-dimensional organic conductor α\alpha-(BEDT-TTF)2_2KHg(SCN)4_4

We have used a low-frequency magneto-thermopower (MTEP) method to probe the high magnetic field ground state behavior of $\alpha$-(BEDT-TTF)$_2$KHg(SCN)$_4$ along all three principal crystallographic axes at low temperatures. The thermopower tensor coefficients ($S_{xx}, S_{yx}$ and $S_{zz}$) have been measured to 30 T, beyond the anomalous low temperature, field-induced transition at 22.5 T. We find a significant anisotropy in the MTEP signal, and also observe large quantum oscillations associated with the de Haas - van Alphen effect. The anisotropy indicates that the ground state properties are clearly driven by mechanisms that occur along specific directions for the in-plane electronic structure. Both transverse and longitudinal magnetothermopower show asymptotic behavior in field, which can be explained in terms of magnetic breakdown of compensated closed orbits.Comment: 9 pages, 10 figure

The Frequency Dependence of Critical-velocity Behavior in Oscillatory Flow of Superfluid Helium-4 Through a 2-micrometer by 2-micrometer Aperture in a Thin Foil

The critical-velocity behavior of oscillatory superfluid Helium-4 flow through a 2-micrometer by 2-micrometer aperture in a 0.1-micrometer-thick foil has been studied from 0.36 K to 2.10 K at frequencies from less than 50 Hz up to above 1880 Hz. The pressure remained less than 0.5 bar. In early runs during which the frequency remained below 400 Hz, the critical velocity was a nearly-linearly decreasing function of increasing temperature throughout the region of temperature studied. In runs at the lowest frequencies, isolated 2 Pi phase slips could be observed at the onset of dissipation. In runs with frequencies higher than 400 Hz, downward curvature was observed in the decrease of critical velocity with increasing temperature. In addition, above 500 Hz an alteration in supercritical behavior was seen at the lower temperatures, involving the appearance of large energy-loss events. These irregular events typically lasted a few tens of half-cycles of oscillation and could involve hundreds of times more energy loss than would have occurred in a single complete 2 Pi phase slip at maximum flow. The temperatures at which this altered behavior was observed rose with frequency, from ~ 0.6 K and below, at 500 Hz, to ~ 1.0 K and below, at 1880 Hz.Comment: 35 pages, 13 figures, prequel to cond-mat/050203

Effectiveness of the global protected area network in representing species diversity

The Fifth World Parks Congress in Durban, South Africa, announced in September 2003 that the global network of protected areas now covers 11.5% of the planet's land surface. This surpasses the 10% target proposed a decade earlier, at the Caracas Congress, for 9 out of 14 major terrestrial biomes. Such uniform targets based on percentage of area have become deeply embedded into national and international conservation planning. Although politically expedient, the scientific basis and conservation value of these targets have been questioned. In practice, however, little is known of how to set appropriate targets, or of the extent to which the current global protected area network fulfils its goal of protecting biodiversity. Here, we combine five global data sets on the distribution of species and protected areas to provide the first global gap analysis assessing the effectiveness of protected areas in representing species diversity. We show that the global network is far from complete, and demonstrate the inadequacy of uniform—that is, 'one size fits all'—conservation targets

Periodic orbit resonances in layered metals in tilted magnetic fields

The frequency dependence of the interlayer conductivity of a layered Fermi liquid in a magnetic field which is tilted away from the normal to the layers is considered. For both quasi-one- and quasi-two-dimensional systems resonances occur when the frequency is a harmonic of the frequency at which the magnetic field causes the electrons to oscillate on the Fermi surface within the layers. The intensity of the different harmonic resonances varies significantly with the direction of the field. The resonances occur for both coherent and weakly incoherent interlayer transport and so their observation does not imply the existence of a three-dimensional Fermi surface.Comment: 4 pages, RevTeX + epsf, 2 figures. Discussion of other work revised. To appear in Phys. Rev. B, Rapid Commun., October 1

Phylogeny of Geomydoecus and Thomomydoecus pocket gopher lice (phthiraptera, trichodectidae) inferred from cladistic analysis of adult and first instar morphology

The phylogeny for all 122 species and subspecies of chewing lice of the genera Geomydoecus and Thomomydoecus (Phthiraptera: Trichodectidae) hosted by pocket gophers (Rodentia: Geomyidae) is estimated by a cladistic analysis of fifty-eight morphological characters obtained from adults and first instars. The data set has considerable homoplasy, but still contains phylogenetic information. The phylogeny obtained is moderately resolved and, with some notable exceptions, supports the species complexes proposed by Hellenthal and Price over the the last two decades. The subgenera G. (Thaelerius) and T. (Thomomydoecus) are both shown to be monophyletic, but the monophly of subgenus T. (Jamespattonius) could not be confirmed, perhaps due to the lack of first-instar data for one of its component species. The nominate subgenus of Geomydoecus may be monophyletic, but our cladogram was insufficiently resolved to corroborate this. Mapping the pocket gopher hosts onto the phylogeny reveals a consistent pattern of louse clades being restricted to particular genera or subgenera of gophers, but the history of the host-parasite association appears complex and will require considerable effort to resolve

Muon anomalous magnetic moment, lepton flavor violation, and flavor changing neutral current processes in SUSY GUT with right-handed neutrino

Motivated by the large mixing angle solutions for the atmospheric and solar neutrino anomalies, flavor changing neutral current processes and lepton flavor violating processes as well as the muon anomalous magnetic moment are analyzed in the framework of SU(5) SUSY GUT with right-handed neutrino. In order to explain realistic mass relations for quarks and leptons, we take into account effects of higher dimensional operators above the GUT scale. It is shown that the supersymmetric (SUSY) contributions to the CP violation parameter in $K^0-\bar{K}^0$ mixing, $\epsilon_K$, the $\mu \to e \gamma$ branching ratio, and the muon anomalous magnetic moment become large in a wide range of parameter space. We also investigate correlations among these quantities. Within the current experimental bound of $\text{B}(\mu \to e \gamma)$, large SUSY contributions are possible either in the muon anomalous magnetic moment or in $\epsilon_K$. In the former case, the favorable value of the recent muon anomalous magnetic moment measurement at the BNL E821 experiment can be accommodated. In the latter case, the allowed region of the Kobayashi-Maskawa phase can be different from the prediction within the Standard Model (SM) and therefore the measurements of the CP asymmetry of $B\to J/\psi K_S$ mode and $\Delta m_{B_s}$ could discriminate this case from the SM. We also show that the $\tau \to \mu \gamma$ branching ratio can be close to the current experimental upperbound and the mixing induced CP asymmetry of the radiative B decay can be enhanced in the case where the neutrino parameters correspond to the Mikheyev-Smirnov-Wolfenstein small mixing angle solution.Comment: 70 pages, 14 figure