7 research outputs found
Evidence for nodal superconductivity in LaFePO
In several iron-arsenide superconductors there is strong evidence for a fully
gapped superconducting state consistent with either a conventional s-wave
symmetry or an unusual state where there the gap changes sign between
the electron and hole Fermi surface sheets. Here we report measurements of the
penetration depth in very clean samples of the related
iron-phosphide superconductor, LaFePO, at temperatures down to 100 mK.
We find that varies almost perfectly linearly with strongly
suggesting the presence of gap nodes in this compound. Taken together with
other data, this suggests the gap function may not be generic to all pnictide
superconductors
Single crystal of superconducting SmFeAsO1-xFy grown at high pressure
Single crystals of SmFeAsO1-xFy of a size up to 120 micrometers have been
grown from NaCl/KCl flux at a pressure of 30 kbar and temperature of 1350-1450
C using the cubic anvil high-pressure technique. The superconducting transition
temperature of the obtained single crystals varies between 45 and 53 K.Obtained
crystals are characterized by a full diamagnetic response in low magnetic
fields and by a high critical current density in high magnetic fields.
Structural refinement has been performed on single crystal. Differential
thermal analysis investigations at 1 bar Ar pressure show decomposition of
SmFeAsO1-xFy at 1302 C.Comment: 12 pages, 3 tables, 6 figure
Microwave response of superconducting pnictides: extended scenario
We consider a two-band superconductor with relative phase between the
two order parameters as a model for the superconducting state in
ferropnictides. Within this model we calculate the microwave response and the
NMR relaxation rate. The influence of intra- and interband impurity scattering
beyond the Born and unitary limits is taken into account. We show that,
depending on the scattering rate, various types of power law temperature
dependencies of the magnetic field penetration depth and the NMR relaxation
rate at low temperatures may take place.Comment: 11 pages, 5 figure
High-pressure growth of fluorine-free SmFeAsO superconducting single crystals
Superconducting single crystals of SmFeAsO without fluorine doping
were grown at a pressure of 3.3 GPa and a temperature of 1350-1450 C by
using the self-flux method. Plate-like single crystals of a few-150 m in
their lateral size were obtained. Single crystals showed the superconducting
transition at about 53.5 K with a narrow transition width of 0.5 K. The
synchrotron-irradiated x-ray diffractometry patterns and
high-angle-annular-dark-field scanning transmission electron microscopy images
point to the high quality of the crystals with a well-defined layered
tetragonal structure. The chemical compositions of the crystals were estimated
by using the electron-probe x-ray microanalysis.Comment: 12 pages, 3 figure
Nuclear magnetic relaxation and superfluid density in Fe-pnictide superconductors: An anisotropic \pm s-wave scenario
We discuss the nuclear magnetic relaxation rate and the superfluid density
with the use of the effective five-band model by Kuroki et al. [Phys. Rev.
Lett. 101, 087004 (2008)] in Fe-based superconductors. We show that a
fully-gapped anisotropic \pm s-wave superconductivity consistently explains
experimental observations. In our phenomenological model, the gaps are assumed
to be anisotropic on the electron-like \beta Fermi surfaces around the M point,
where the maximum of the anisotropic gap is about four times larger than the
minimum.Comment: 10 pages, 8 figures; Submitted versio