53 research outputs found
High-field phase-diagram of Fe arsenide superconductors
Here, we report an overview of the phase diagram of single layered and double
layered Fe arsenide superconductors at high magnetic fields. Our systematic
magnetotransport measurements of polycrystalline SmFeAsOF at
different doping levels confirm the upward curvature of the upper critical
magnetic field as a function of temperature defining the phase
boundary between the superconducting and metallic states for crystallites with
the ab planes oriented nearly perpendicular to the magnetic field. We further
show from measurements on single crystals that this feature, which was
interpreted in terms of the existence of two superconducting gaps, is
ubiquitous among both series of single and double layered compounds. In all
compounds explored by us the zero temperature upper critical field ,
estimated either through the Ginzburg-Landau or the Werthamer-Helfand-Hohenberg
single gap theories, strongly surpasses the weak coupling Pauli paramagnetic
limiting field. This clearly indicates the strong coupling nature of the
superconducting state and the importance of magnetic correlations for these
materials. Our measurements indicate that the superconducting anisotropy, as
estimated through the ratio of the effective masses for carriers moving along the c-axis and the ab planes,
respectively, is relatively modest as compared to the high- cuprates, but
it is temperature, field and even doping dependent. Finally, our preliminary
estimations of the irreversibility field , separating the vortex-solid
from the vortex-liquid phase in the single layered compounds, indicates that it
is well described by the melting of a vortex lattice in a moderately
anisotropic uniaxial superconductor.Comment: 12 pages, for Physica C, special issue on the Fe oxypnictides
(revised version
Giant suppression of phononic heat transport in a quantum magnet BiCu2PO6
Thermal transport of quantum magnets has elucidated the nature of low energy elementary excitations and complex interplay between those excited states via strong scattering of thermal carriers. BiCu2PO6 is a unique frustrated spin-ladder compound exhibiting highly anisotropic spin excitations that contain both itinerant and localized dispersion characters along the b-and a-axes respectively. Here, we investigate thermal conductivity Îș of BiCu2PO6 under high magnetic fields (H) of up to 30 tesla. A dip-feature in Îș, located at âŒ15 K at zero-H along all crystallographic directions, moves gradually toward lower temperature (T) with increasing H, thus resulting in giant suppression by a factor of âŒ30 near the critical magnetic field of Hc â° 23.5 tesla. The giant H-and T-dependent suppression of Îș can be explained by the combined result of resonant scattering of phononic heat carriers with magnetic energy levels and increased phonon scattering due to enhanced spin fluctuation at Hc, unequivocally revealing the existence of strong spin-phonon coupling. Moreover, we find an experimental indication that the remaining magnetic heat transport along the b-axis becomes almost gapless at the magnetic quantum critical point realized at Hc. © 2016 The Author(s)1441sciescopu
Diazotrophic Endophytes of Poplar and Willow for Growth Promotion of Rice Plants in NitrogenâLimited Conditions
Differential responses of nematode communities to soybean genotypes resistant and susceptible to Heterodera glycines race 3
Predicting Osteoporosis by Analyzing Fracture Risk Factors and Trabecular Microarchitectures of the Proximal Femur from DXA Images
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