8 research outputs found
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
Angular dependence of resistivity in the superconducting state of NdFeAsOF single crystals
We report the results of angle dependent resistivity of
NdFeAsOF single crystals in the superconducting state. By
doing the scaling of resistivity within the frame of the anisotropic
Ginzburg-Landau theory, it is found that the angle dependent resistivity
measured under different magnetic fields at a certain temperature can be
collapsed onto one curve. As a scaling parameter, the anisotropy can
be determined for different temperatures. It is found that
increases slowly with decreasing temperature, varying from 5.48
at T=50 K to 6.24 at T=44 K. This temperature dependence can be
understood within the picture of multi-band superconductivity.Comment: 7 pages, 4 figure
Pairing symmetry and properties of iron-based high temperature superconductors
Pairing symmetry is important to indentify the pairing mechanism. The
analysis becomes particularly timely and important for the newly discovered
iron-based multi-orbital superconductors. From group theory point of view we
classified all pairing matrices (in the orbital space) that carry irreducible
representations of the system. The quasiparticle gap falls into three
categories: full, nodal and gapless. The nodal-gap states show conventional
Volovik effect even for on-site pairing. The gapless states are odd in orbital
space, have a negative superfluid density and are therefore unstable. In
connection to experiments we proposed possible pairing states and implications
for the pairing mechanism.Comment: 4 pages, 1 table, 2 figures, polished versio
Point contact Andreev reflection spectroscopy of NdFeAsO_0.85
The newly discovered oxypnictide family of superconductors show very high
critical temperatures of up to 55K. Whilst there is growing evidence that
suggests a nodal order parameter, point contact Andreev reflection spectroscopy
can provide crucial information such as the gap value and possibly the number
of energy gaps involved. For the oxygen deficient NdFeAsO0.85 with a Tc of
45.5K, we show that there is clearly a gap value at 4.2K that is of the order
of 7meV, consistent with previous studies on oxypnictides with lower Tc.
Additionally, taking the spectra as a function of gold tip contact pressure
reveals important changes in the spectra which may be indicative of more
complex physics underlying this structure.Comment: 11 pages, 3 figures. New references included, extra discussion. This
version is accepted in Superconductor Science and Technolog
Multiband magnetism and superconductivity in Fe-based compounds
Recent discovery of superconductivity in Fe-based layered compounds may
have opened a new pathway to the room temperature superconductivity. A model Hamiltonian
describing FeAs layers is introduced, highlighting the crucial role of puckering of As atoms
in promoting d electron itinerancy and warding
off large local-moment magnetism of Fe ions, the main enemy of superconductivity. Quantum
many-particle effects in charge, spin and multiband channels are explored and a nesting-induced
spin density-wave order is found in the parent compund. We argue that this largely itinerant
antiferromagnetism and high Tc itself
are essentially tied to the multiband nature of the Fermi surface