Mechanism for Explaining Differences in the Order Parameters of FeAs-Based and FeP-Based Pnictide Superconductors

Abstract

We put forward a scenario that explains the difference between the order-parameter character in arsenide (As) and phosphorous (P) iron-based superconductors. Using functional renormalization group to analyze it in detail, we find that nodal superconductivity on the electron pockets (hole pocket gaps are always nodeless) can naturally appear when the hole pocket at (π,π) in the unfolded Brillouin zone is absent, as is the case in LaOFeP. There, electron-electron interactions render the gap on the electron pockets softly nodal (of s(±) form). When the pocket of d(xy) orbital character is present, intraorbital interactions with the d(xy) part of the electron Fermi surface drives the superconductivity nodeless.

s-wave superconductivity with orbital-dependent sign change in checkerboard models of iron-based superconductors

“…However, they are consistent with the results of many previous studies 2,4,12,13 , using other models and methods. The pairing symmetry is dominated by the A 1g channel.…”

“…It is highly debated that whether the iron-based superconductors belong to the same category of strongly correlated electron systems as the cuprates. Models based on both strong coupling 2-9 and weak coupling [10][11][12][13][14][15][16] approaches have been applied to understand the properties of these materials and their relation to the curpates.…”

“…The parent compounds of ironpnictides are metallic rather than insulating. So far, the majority of theories for the pairing symmetry of iron-based superconductors are based on weak coupling approaches [10][11][12][13][14][15][16] . Although there are discrepancies, the theories based on these approaches have reached a broad consensus regarding the pairing symmetries in ironbased superconductors: for optimally hole doped ironpnictides, for example, Ba 0.6 K 0.4 Fe 2 As 2 , an extended s-wave pairing symmetry, called s ± , is favored 10 , as a result of repulsive interband interactions and nesting between the hole and electron pockets.…”

Fermi Surface, Pressure-Induced Antiferromagnetic Order, and Superconductivity in FeSe

“…The relation between the structural transition and the magnetic ordered phase has been a controversial issue, the understanding of which may provide insights into the pairing mechanism and symmetry. [2][3][4][5][6][7][8] To elucidate the origin of the structural transition above the magnetic order, spin-nematic theory 9,10) and orbital order theory 11,12) have been intensively proposed. The microscopic pictures of these theories are the spin-quadrupole order induced by the spin fluctuation 9) and the orbital-spin mode-coupling characterized by the Aslamazov-Larkin vertex correction, 12) respectively.…”

Robustness ofs-Wave Pairing in Electron-OverdopedA1−yFe2−xSe2Fang1, Wu2, Thomale3 et al. 2011Phys. Rev. XSelf Cite9751141View full textAdd to dashboardCite

“…For extremely holedoped materials, such as KFe 2 As 2 , the absence of electron pockets can lead to a d-wave pairing symmetry [18] with a low transition temperature. For electron-doped materials such as Ba 2 Fe 2Àx Co x As 2 , the anisotropy of the superconducting gap around the electron pockets in the s AE state grows for larger electron doping, and eventually the superconducting gap develops nodes around the electron pockets due to the weakening of the nesting condition and the increase of the d xy orbital weight at the electron pocket Fermi surfaces [39,40]. Finally, in the limit of the heavily electron-doped case when the hole pockets vanish and only the electron pockets are left, the d-wave pairing symmetry may be favored again [18,41,42].…”