Superconductivity and Anti Ferromagnetic Spin Density wave in Iron based Superconductors
No Thumbnail Available
Date
2015-01
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
The interplay between magnetism and superconductivity had attracted immence
interest and effort following the discovery of magnetic superconductors like
heavy fermion, cuprate and recent iron based superconductors (FebSC). The study
of their interplay between has also been fascinating area of study due to complex
magnetic interactions in the systems. In the latest, FebSCs the competition
between antiferromagnetic (AFM) spin density wave (SDW) and
superconductivity (SC) has attracted considerable attention in the current research
in the field of superconductivity. The magnetic order in most FebSCs is the result
of nesting between hole and electron pockets found at the the center and corners
of the unfolded Brillouin zones. The interaction between fermions forming these
pockets is important to study the low temperature physics of FebSCs. The model
Hamiltonian consisting of these fermions responsible for magnetic and
superconducting pairing interactions is developed to study their interplay. Using
either Green function or Bogoligiv transformation method gap equations for
SDW and s- wave superconductivity order parameters have been established for
pure systems and for interacting ones. The gap equations have been studied in
detail as physically accepted choice of parameters. We have established
experimentally accepted Electronic Phase diagrams for some FebSCs. First we
study the interplay between sign reversal s-wave symmetry superconductivity
(SC+-) and SDW order parameters and found their homogeneous microscopic
coexistence in under doped region. On the other hand the competition between
sign preserving s-wave superconductivity (SC++) and SDW order parameters
produce their homogeneous overlap near quantum critical point which is
vi ABSTRACT
consistent with the phase diagram of electron doped LaFeAsF compounds.
When the magnetic order is commensurate SDW (SDWc) the interplay calculation
presents the first order transition from SDW to SC++ which is consistent with the
phase separated doped FebSCs compounds like doped Li Fe As compounds.
The first model calculation results can be compared with the experimental report
of doped Ba Fe2 As2 iron based families, doped Sm Fe AsO and electron
doped LaFe As compounds. Even more interestingly, the result of our study
showed first order transition from SDWc to incommensurate SDW (SDWδ) which
is directly related to the observed magnetic orders near optimal doped region of
Ba Fe2 As2. The strong suppression of SDW order parameter in the SC phases
and the suppression of superconductivity in both under doped and over doped
regions are some of the interesting results
Description
Keywords
Iron based Superconductors