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Title: Concealed d -wave pairs in the s ± condensate of iron-based superconductors

A central question in iron-based superconductivity is the mechanism by which the paired electrons minimize their strong mutual Coulomb repulsion. In most unconventional superconductors, Coulomb repulsion is minimized through the formation of higher angular momentum Cooper pairs, with Fermi surface nodes in the pair wavefunction. The apparent absence of such nodes in the iron-based superconductors has led to a belief they form an s-wave (s±) singlet state, which changes sign between the electron and hole pockets. However, the multiorbital nature of these systems opens an alternative possibility. In this paper, we propose a new class of s± state containing a condensate of d-wave Cooper pairs, concealed by their entanglement with the iron orbitals. By combining the d-wave (L=2) motion of the pairs with the internal angular momenta I =2 of the iron orbitals to make a singlet (J =L+I =0), an s± superconductor with a nontrivial topology is formed. This scenario allows us to understand the development of octet nodes in potassium-doped Ba1$-$xKXFe2As2 as a reconfiguration of the orbital and internal angular momentum into a high spin (J =L+I =4) state; the reverse transition under pressure into a fully gapped state can then be interpreted as a return to themore » low-spin singlet. Finally, the formation of orbitally entangled pairs is predicted to give rise to a shift in the orbital content at the Fermi surface, which can be tested via laser-based angle-resolved photoemission spectroscopy.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Rutgers Univ., Piscataway, NJ (United States). Dept. of Physics and Astronomy
  2. Rutgers Univ., Piscataway, NJ (United States). Dept. of Physics and Astronomy; Royal Holloway Univ. of London (United Kingdom). Dept. of Physics
  3. Karlsruhe Inst. of Technology (KIT) (Germany). Inst. for Theory of Condensed Matter and DFG Center for Functional Nanostructures
Publication Date:
OSTI Identifier:
1250546
Grant/Contract Number:
FG02-99ER45790
Type:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 113; Journal Issue: 20; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Research Org:
Rutgers Univ., Piscataway, NJ (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; superconductivity; iron-based superconductors; unconventional superconductivity; strongly correlated electrons