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Order‐parameter anisotropies in the pnictides: An optimization principle for multi‐band superconductivity
Author(s) -
Hanke W.,
Platt Ch.,
Thomale R.
Publication year - 2011
Publication title -
annalen der physik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.009
H-Index - 68
eISSN - 1521-3889
pISSN - 0003-3804
DOI - 10.1002/andp.201100035
Subject(s) - physics , pairing , fermi surface , superconductivity , position and momentum space , coulomb , condensed matter physics , symmetry (geometry) , anisotropy , wave function , renormalization , quantum mechanics , electron , momentum (technical analysis) , space (punctuation) , computer science , geometry , mathematics , finance , economics , operating system
Using general arguments of an optimization taking place between the pair wave function and the repulsive part of the electron‐electron interaction, we analyze the superconducting gap in materials with multiple Fermi‐surface (FS) pockets, with exemplary application to two proto‐type ferropnictide setups. The main point of our work is to show that the SC state, its gap, and, in particular, its anisotropy in momentum space is determined by an optimization which determines and optimizes the interplay between the attractive interaction in the SC‐channel and the Coulomb repulsion . This optimization problem is unavoidable in a multi‐band SC situation: for the pnictides, it appears because of a frustration in the s ± ‐channel, when more than two FS‐pockets are involved in setting up the pairing interaction. On the basis of functional renormalization group (FRG) calculations for a wide parameter span of the bare interactions, we show that the symmetry of the gap and the nodal versus nodeless behavior is driven by this optimization requirement.