47 research outputs found
Superconductivity and magnetism in platinum-substituted SrFe2As2 single crystals
Single crystals of SrFe2-xPtxAs2 (0 < x < 0.36) were grown using the self
flux solution method and characterized using x-ray crystallography, electrical
transport, magnetic susceptibility, and specific heat measurements. The
magnetic/structural transition is suppressed with increasing Pt concentration,
with superconductivity seen over the range 0.08 < x < 0.36 with a maximum
transition temperature Tc of 16 K at x = 0.16. The shape of the phase diagram
and the changes to the lattice parameters are similar to the effects of other
group VIII elements Ni and Pd, however the higher transition temperature and
extended range of superconductivity suggest some complexity beyond the simple
electron counting picture that has been discussed thus far.Comment: 6 pages, 6 figure
Evidence of a universal and isotropic 2\Delta/kBTC ratio in 122-type iron pnictide superconductors over a wide doping range
We have systematically investigated the doping and the directional dependence
of the gap structure in the 122-type iron pnictide superconductors by point
contact Andreev reflection spectroscopy. The studies were performed on single
crystals of Ba1-xKxFe2As2 (x = 0.29, 0.49, and 0.77) and SrFe1.74Co0.26As2 with
a sharp tip of Pb or Au pressed along the c-axis or the ab-plane direction. The
conductance spectra obtained on highly transparent contacts clearly show
evidence of a robust superconducting gap. The normalized curves can be well
described by the Blonder-Tinkham-Klapwijk model with a lifetime broadening. The
determined gap value scales very well with the transition temperature, giving
the 2{\Delta}/kBTC value of ~ 3.1. The results suggest the presence of a
universal coupling behavior in this class of iron pnictides over a broad doping
range and independent of the sign of the doping. Moreover, conductance spectra
obtained on c-axis junctions and ab-plane junctions indicate that the observed
gap is isotropic in these superconductors
Extreme magnetic field-boosted superconductivity
Applied magnetic fields underlie exotic quantum states, such as the
fractional quantum Hall effect and Bose-Einstein condensation of spin
excitations. Superconductivity, on the other hand, is inherently antagonistic
towards magnetic fields. Only in rare cases can these effects be mitigated over
limited fields, leading to reentrant superconductivity. Here, we report the
unprecedented coexistence of multiple high-field reentrant superconducting
phases in the spin-triplet superconductor UTe2. Strikingly, we observe
superconductivity in the highest magnetic field range identified for any
reentrant superconductor, beyond 65 T. These extreme properties reflect a new
kind of exotic superconductivity rooted in magnetic fluctuations and boosted by
a quantum dimensional crossover