Doping and Irradiation Controlled Vortex Pinning Behavior in BaFe2(As1-xPx)2 Single Crystals

We report on the systematic evolution of vortex pinning behavior in isovalent doped single crystals of BaFe2(As1-xPx)2. Proceeding from optimal doped to ovedoped samples, we find a clear transfor- mation of the magnetization hysteresis from a fishtail behavior to a distinct peak effect followed by a reversible magnetization and Bean Livingston surface barriers. Strong point pinning dominates the vortex behavior at low fields whereas weak collective pinning determines the behavior at higher fields. In addition to doping effects, we show that particle irradiation by energetic protons can tune vortex pinning in these materials.Comment: 4 pages, 4 figures,significant change of eraly version, accepted by PRB rapid communication

Persistence to high temperatures of interlayer coherence in an organic superconductor

The interlayer magnetoresistance $\rho_{zz}$ of the organic metal \cuscn is studied in fields of up to 45 T and at temperatures $T$ from 0.5 K to 30 K. The peak in $\rho_{zz}$ seen in in-plane fields, a definitive signature of interlayer coherence, remains to $T$s exceeding the Anderson criterion for incoherent transport by a factor $\sim 30$. Angle-dependent magnetoresistance oscillations are modeled using an approach based on field-induced quasiparticle paths on a 3D Fermi surface, to yield the $T$ dependence of the scattering rate $\tau^{-1}$. The results suggest that $\tau^{-1}$ does not vary strongly over the Fermi surface, and that it has a $T^2$ dependence due to electron-electron scattering

Upper critical field study in the organic superconductor β′′\beta''-(ET)2_{2}SF5_{5}CH2_{2}CF2_{2}SO3_{3} : Possibility of Fulde-Ferrell-Larkin-Ovchinnikov state

We report upper critical field measurements in the metal-free-all-organic superconductor $\beta''$-(ET)$_{2}$SF$_{5}$CH$_{2}$CF$_{2}$SO$_{3}$ obtained from measuring the in-plane penetration depth using the tunnel diode oscillator technique. For magnetic field applied parallel to the conducting planes the low temperature upper critical fields are found to exceed the Pauli limiting field calculated by using a semi-empirical method. Furthermore, we found a signature that could be the phase transition between the superconducting vortex state and the Fulde-Ferrell-Larkin-Ovchinnikov state in the form of a kink just below the upper critical field and only at temperatures below 1.23 K.Comment: 4 pages, 6 figure

Universal temperature dependence of the London penetration depth in κ−(ET)2X superconductors

High-precision radio-frequency magnetic susceptibility measurements were performed on single crystals of fully deuterated kappa-(ET)(2)Cu[N(CN)(2)]Br, hereafter designated as kappa-(D8 ET)(2)Cu[N(CN)(2)]Br. This material phase separates into superconducting and antiferromagnetic regions, the degree of which depends strongly upon the cooling rate. We show that the screening fraction rise varies logarithmically with the cooling rate over nearly five decades. The average size of superconducting regions is estimated to vary from 5 to 40 mu m, depending upon cooling rate, consistent with previous infrared microscopy measurements. In the region T less than or similar to T-c/3, the effective magnetic penetration depth exhibits power-law behavior lambda(T) - lambda(0) similar to T-n with n = 1.6, independent of the cooling rate. Changes in cooling rate and the consequent phase separation evidently do not introduce the kind of disorder that would alter the exponent n in a d-wave superconductor. The exponent remains close to n = 1.5, reported in single crystals of kappa-(ET)(2)Cu[N(CN)(2)]Br and kappa-(ET)(2)Cu(NCS)(2) [A. Carrington et al., Phys. Rev. Lett 83. 4172 (1999)]. The transition temperature fell linearly with 1 - eta(sc). Measurements were also made on kappa-(ET)(2)Cu[N(CN)(2)]Cl of normal isotopic abundance in which a very small amount of superconducting phase rise eta(sc) approximate to 10(-4) developed, presumably through the strain-induced sample mounting. This material showed a power-law exponent of n = 1.64, independent of the cooling rate

Comparison of the Fermi-surface topologies of kappa-(BEDT-TTF)_2 Cu(NCS)_2 and its deuterated analogue

We have measured details of the quasi one-dimensional Fermi-surface sections in the organic superconductor kappa-(BEDT-TTF)_2 Cu(NCS)_2 and its deuterated analogue using angle-dependent millimetre-wave techniques. There are significant differences in the corrugations of the Fermi surfaces in the deuterated and undeuterated salts. We suggest that this is important in understanding the inverse isotope effect, where the superconducting transition temperature rises on deuteration. The data support models for superconductivity which invoke electron-electron interactions depending on the topological properties of the Fermi surface

Empiric Models of the Earth's Free Core Nutation

Free core nutation (FCN) is the main factor that limits the accuracy of the modeling of the motion of Earth's rotational axis in the celestial coordinate system. Several FCN models have been proposed. A comparative analysis is made of the known models including the model proposed by the author. The use of the FCN model is shown to substantially increase the accuracy of the modeling of Earth's rotation. Furthermore, the FCN component extracted from the observed motion of Earth's rotational axis is an important source for the study of the shape and rotation of the Earth's core. A comparison of different FCN models has shown that the proposed model is better than other models if used to extract the geophysical signal (the amplitude and phase of FCN) from observational data.Comment: 8 pages, 3 figures; minor update of the journal published versio

An Experimental and Semi-Empirical Method to Determine the Pauli-Limiting Field in Quasi 2D Superconductors as applied to κ\kappa-(BEDT-TTF)2_2Cu(NCS)2_2: Strong Evidence of a FFLO State

We present upper critical field data for $\kappa$-(BEDT-TTF)$_2$Cu(NCS)$_2$ with the magnetic field close to parallel and parallel to the conducting layers. We show that we can eliminate the effect of vortex dynamics in these layered materials if the layers are oriented within 0.3 degrees of parallel to the applied magnetic field. Eliminating vortex effects leaves one remaining feature in the data that corresponds to the Pauli paramagnetic limit ($H_p$). We propose a semi-empirical method to calculate the $H_p$ in quasi 2D superconductors. This method takes into account the energy gap of each of the quasi 2D superconductors, which is calculated from specific heat data, and the influence of many body effects. The calculated Pauli paramagnetic limits are then compared to critical field data for the title compound and other organic conductors. Many of the examined quasi 2D superconductors, including the above organic superconductors and CeCoIn$_5$, exhibit upper critical fields that exceed their calculated $H_p$ suggesting unconventional superconductivity. We show that the high field low temperature state in $\kappa$-(BEDT-TTF)$_2$Cu(NCS)$_2$ is consistent with the Fulde Ferrell Larkin Ovchinnikov state.Comment: 8 pages, 9 figures, 10 years of dat

Integration of physical and genetic maps of common bean through BAC-derived microsatellite markers

<p>Abstract</p> <p>Background</p> <p>Common bean (<it>Phaseolus vulgaris </it>L.) is the most important legume for direct human consumption and the goal of this study was to integrate a recently constructed physical map for the species with a microsatellite based genetic map using a BAC library from the genotype G19833 and the recombinant inbred line population DOR364 × G19833.</p> <p>Results</p> <p>We searched for simple sequence repeats (SSRs) in the 89,017 BAC-end sequences (BES) from the physical map and genetically mapped any polymorphic BES-SSRs onto the genetic map. Among the BES it was possible to identify 623 contig-linked SSRs, most of which were highly AT-rich. A subgroup of 230 di-nucleotide and tri-nucleotide based SSR primer pairs from these BACs was tested on the mapping parents with 176 single copy loci and 114 found to be polymorphic markers. Of these, 99 were successfully integrated into the genetic map. The 99 linkages between the genetic and physical maps corresponded to an equal number of contigs containing a total of 5,055 BAC clones.</p> <p>Conclusions</p> <p>Class II microsatellites were more common in the BES than longer class I microsatellites. Both types of markers proved to be valuable for linking BAC clones to the genetic map and were successfully placed across all 11 linkage groups. The integration of common bean physical and genetic maps is an important part of comparative genome analysis and a prelude to positional cloning of agronomically important genes for this crop.</p