Abstract

We elucidate a recently emergent framework in unifying the two families of high temperature (high Tc) superconductors, cuprates and iron-based superconductors. The unification suggests that the latter is simply the counterpart of the former to realize robust extended s-wave pairing symmetries in a square lattice. The unification identifies that the key ingredients (gene) of high Tc superconductors is a quasi two dimensional electronic environment in which the d-orbitals of cations that participate in strong in-plane couplings to the p-orbitals of anions are isolated near Fermi energy. With this gene, the superexchange magnetic interactions mediated by anions could maximize their contributions to superconductivity. Creating the gene requires special arrangements between local electronic structures and crystal lattice structures. The speciality explains why high Tc superconductors are so rare. An explicit prediction is made to realize high Tc superconductivity in Co/Ni-based materials with a quasi two dimensional hexagonal lattice structure formed by trigonal bipyramidal complexes.

Highlights

  • Almost three decades ago, the first family of unconventional high Tc superconductors, cuprates [1], was discovered

  • This path stems from a simple framework that unifies cuprates and iron-based superconductors based on previous understandings in repulsive interaction or magnetically driven high Tc mechanisms

  • A general search procedure can be: (1) design a possible lattice structure that can be constructed by certain cation–anion complexes; (2) use symmetry tools to understand local electronic physics; (3) perform standard density functional theory (DFT) calculations to obtain band structures and its orbital characters; (4) apply the gene requirements to determine conditions and likelihood on the existence of high Tc superconducting environment; (5) design realistic materials whose lattice structures can be stabilized

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Summary

Introduction

The first family of unconventional high Tc superconductors, cuprates [1], was discovered. By taking the assumption that a common superconducting mechanism is shared by both known high Tc superconductors, we elucidate a recently emergent path to end the deadlock in solving high Tc mechanism by implementing inductive reasoning to reexamine the high Tc problem [3, 4] This path stems from a simple framework that unifies cuprates and iron-based superconductors based on previous understandings in repulsive interaction or magnetically driven high Tc mechanisms. It suggests that iron-based superconductors are the counterpart of cuprates to realize robust extended s-wave pairing symmetries in a square lattice Both materials share a key ingredient, the gene of unconventional high Tc superconductivity: a quasi two dimensional electronic environment in which the d-orbitals of cation atoms that participate in strong in-plane couplings to the p-orbitals of anion atoms are isolated near Fermi energy. The prediction will establish powerful guiding principles to search for high Tc superconductor candidates, as well as to settle the debate on unconventional high Tc superconducting mechanism

Questions for unconventional high Tc superconductivity
The ansatz to the first question
The case of cuprates
The case of iron-based superconductors
The answer to the second question
Conditions and rules for unconventional high Tc superconductivity
The case of curpates
The answer to the third question
Discussion
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