Search the Genes of Unconventional High Temperature Superconductors

Abstract

We discuss two basic principles to unify the understanding of both cuprates and iron-based superconductors: (1) the correspondence principle— the short range magnetic exchange interactions and the Fermi surfaces act collaboratively to achieve high Tc superconductivity and determine pairing symmetries; (2) the selective magnetic pairing rule: the superconductivity is only induced by the magnetic exchange couplings from the superexchange mechanism through cation-anion-cation chemical bondings but not those from direct exchange couplings resulted from the direct cation's d-d chemical bondings. These two principles provide a unified explanation why the d-wave pairing symmetry and the s-wave pairing symmetry are robust respectively in cuprates and iron-based superconductors. In the meanwhile, the above two principles can serve as direct guiding rules to search new unconventional high Tc superconductors. We propose that the third classes of unconventional high Tc superconducting candidates in compounds formed by cation-anion trigonal bipyramidal complexes with a d7 filling configuration on the cation ions. Their superconducting states are expected to be dominated by the d+id pairing symmetry. Synthesizing these compounds and verifying the prediction can convincingly establish the high Tc superconducting mechanism and pave a way to design new high Tc superconductors