Download Electronic structure of iron-based superconductors and

Electronic structure of iron-based superconductors and related materials
(Talk #: to be completed by the Organizer)
Dong-Lai Feng*
State Key Laboratory of Surface Physic and Department of Physics, Fudan University, Shanghai
200433, China
*Email of Presenting Author: [email protected]
In this talk, I will present the electronic structure of following newly synthesized iron-based
superconductors and related materials, and try to understand their behaviors in a general
picture.
1. FeSe thin films were fabricated by MBE on the STO substrate. For single layer FeSe, a
superconducting gap of 16 meV is observed on the electron cylinders at zone corner.
However, the electronic structure of the 2ML film is dramatically different from that of
the 1ML film, with the signature of presence of a collinear antiferromagnetic (CAF) order
similar to the iron pnictides. Moreover, the Neel temperature (TN) of the CAF order is
reduced with the increasing film thickness. Our results indicate that the CAF order of
FeSe thin films are very sensitive to the tensile strain.
2. BaTi2As2O is likely a parent compound of recently discovered superconductor NaxBa1xTi2Sb2O (TC=5.5K). The Ti2Pn2O plane provides a new playground of possible high
temperature superconductivity. The electronic band structure and orbital character
show the importance of Ti-Ti direct hopping. Continuous evolution of valence band
spectral weight with temperature suggests strong polaronic effects. The ground state is
likely a CDW state in the strong interaction regime.
3. The electronic structure of the superconductivity/SDW coexisting phase has been
revealed in NaFe1-xCoxAs (x=0.0175), which illustrates their intrinsic non-exclusive nature
in the momentum space. We show that the highly anisotropic but nodeless
superconducting gap distribution on the electron pockets is likely a distinct consequence
of the coexisting SDW order, which puts strong constrains on the pairing symmetry in
theory of iron-based superconductors.
4. In TaFe1.23Te3, a Fe-ladder compound, we find a quasi-two dimensional Fermi surface, and
show that SDW transition is driving by the electronic reconstruction which has been observed
in the parent compound of iron pnictides. The study of TaFe1.23Te3 chain system would give
rise to the construction of analytical solution model and further reveal the high-Tc
superconductivity in iron pnictides.
5. BaFe2(As1-xPx)2 is a rather unique system as its superconducting gap contains line nodes.
After revealing a nodal ring around the Z point in optimally doped BaFe2(As1-xPx)2 (x=0.3),
we have successfully observed the evolution of the nodal gap structure in the overdoped
BaFe2(As1-xPx)2(x=0.5). The gap size is proportional to the Tc, and the nodal ring expands
from Z toward the Gamma point. Our results confirm that the nodal gap behavior here is
not due to the d wave pairing but is introduced by the particular orbital distribution near
Z.
This work is conducted in collaboration with H. C. Xu, Z. R. Ye, Yan Zhang, Q. Q. Ge, M. Xu,
Juan Jiang, Shiyong Tan, X. H. Chen, D. H. Lu. S. Kimura.