Low-temperature specific-heat and thermal-expansion measurements on a single crystal of the heavyfermion superconductor UBe 13 reveal an anomaly in the superconducting state. The evolution of this feature is studied as a function of Th doping on several U 12x Th x Be 13 polycrystals (x # 0.03), giving rise to a new "line of anomalies," T L ͑x͒, in the T -x diagram. The anomaly at T L ͑x͒ marks the precursor of the lower of the two phase transitions at x . x cr ഠ 0.019. Implications for the interpretation of the phase diagram of superconducting U 12x Th x Be 13 are addressed. [S0031-9007(98)

Citrus Huanglongbing (HLB) is a devastating disease of citrus known to be associated with a fastidious, phloem-limited Gram-negative, yet to be cultured bacterium in the genus Candidatus Liberibacter. In the present study we have developed a method to quantify viable Candidatus Liberibacter asiaticus (Las) with the aid of ethidium monoazide (EMA) which can differentiate live from dead cells. First, calibration curves were developed with the aid of quantitative real-time PCR (QPCR) by using a plasmid template consisting of a 703 bp DNA fragment of rplKAJL-rpoBC (β-operon) region. Standard equations were then developed to quantify Las genome equivalents in citrus, periwinkle, and Asian citrus psyllid, Diaphorina citri. To overcome the limitation of quantitative PCR in discriminating between live and dead bacterial cells, EMA was used to inhibit the amplification of DNA from the dead cells of Las in plant samples. By using the standard equations and EMA-QPCR methods developed in this study, we found that the proportion of viable cells in citrus and periwinkle ranged from 17-31% and 16-28%, respectively. It was determined that a minimum bacterial concentration is required for HLB symptom development by quantifying the population of Las in symptomatic and asymptomatic leaves. The EMA-QPCR methodology developed in the present study should provide an accurate assessment of viable HLB pathogen, providing a tool to investigate disease epidemiology and thus act as a crucial component for disease assessment and management.

Abstract:We report specific heat measurements on the Fe-based superconductor BaFe 2 (As 0.7 P 0.3 ) 2 , a material on which previous penetration depth, NMR, and thermal conductivity measurements have observed a high density of low-energy excitations, which have been interpreted in terms of order parameter nodes. Within the resolution of our measurements, the low temperature limiting C/T is found to be linear in field, i.e. we find no evidence for a Volovik effect associated with nodal quasiparticles in either the clean or dirty limit. We discuss possible reasons for this apparent contradiction.

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The mechanism of superconductivity in cuprates remains one of the big challenges of condensed matter physics. High-Tc cuprates crystallize into a layered perovskite structure featuring copper oxygen octahedral coordination. Due to the Jahn Teller effect in combination with the strong static Coulomb interaction, the octahedra in high-Tc cuprates are elongated along the c axis, leading to a 3dx2-y2 orbital at the top of the band structure wherein the doped holes reside. This scenario gives rise to 2D characteristics in high-Tc cuprates that favor d-wave pairing symmetry. Here, we report superconductivity in a cuprate Ba2CuO4-y, wherein the local octahedron is in a very exceptional compressed version. The Ba2CuO4-y compound was synthesized at high pressure at high temperatures and shows bulk superconductivity with critical temperature (Tc) above 70 K at ambient conditions. This superconducting transition temperature is more than 30 K higher than the Tc for the isostructural counterparts based on classical La2CuO4. X-ray absorption measurements indicate the heavily doped nature of the Ba2CuO4-y superconductor. In compressed octahedron, the 3d3z2-r2 orbital will be lifted above the 3dx2-y2 orbital, leading to significant 3D nature in addition to the conventional 3dx2-y2 orbital. This work sheds important light on advancing our comprehensive understanding of the superconducting mechanism of high Tc in cuprate materials.

We present measurements of the specific heat coefficient γ(≡ C/T ) in the low temperature limit as a function of an applied magnetic field for the Fe-based superconductor BaFe2(As0.7P0.3)2. We find both a linear regime at higher fields and a limiting square root H behavior at very low fields. The crossover from a Volovik-like √ H to a linear field dependence can be understood from a multiband calculation in the quasiclassical approximation assuming gaps with different momentum dependence on the hole-and electron-like Fermi surface sheets.

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