3 research outputs found
Nodal Spin Density Wave and band topology of the FeAs based materials
The recently discovered FeAs-based materials exhibit a Spin Density
Wave (SDW) in the undoped state, which gives way to superconductivity upon
doping. Here we show that due to an interesting topological feature of the band
structure, the SDW state cannot acquire a full gap. This is demonstrated within
the SDW mean-field theory of both a simplified two band model and a more
realistic 5-band model. The positions of the nodes are different in the two
models and can be used to detected the validity of each model.Comment: rewritten for clarit
A Numerical Renormalization Group Study of the Superconducting and Spin Density Wave Instabilities in MFeAsOF Compounds
We apply the fermion renormalization group method, implemented numerically by
Honerkamp et.al., to a two-band model of FeAs-based materials. At half filling
we find the or spin density wave order and a sub-dominant
superconducting pairing tendency. Due to a topological reason, the spin density
wave gap has nodes on the fermi surfaces. Away from half filling we find an
unconventional s-wave and a sub-dominant pairing instability. The
former has symmetry around the hole fermi surface but exhibits
symmetry around the electron pockets where the 90 degree
rotation is broken. The pairing mechanism is inter-pocket pair hopping.
Interestingly, the same interaction also drives the antiferromagnetism.Comment: 5 pages, 4 figures, RevTex4. Since the two-band model is insufficient
to describe the iron pnictides, this paper will not be submitted for
publication. Please see arXiv: 0807.0498 for improved work for five-band
mode
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