Balancing act: Evidence for a strong subdominant -wave pairing channel in
We present detailed measurements of the temperature-dependent Raman spectra of optimally doped Ba0.6K0.4Fe2As2 and analyze the low-temperature spectra based on local-density-approximation band-structure calculations and the subsequent estimation of effective Raman vertices. Experimentally, a narrow, emergent mode appears in the B1g (dx2-y2) Raman spectra only below Tc, well into the superconducting state and at an energy below twice the energy gap on the electron Fermi-surface sheets. The Raman spectra can be reproduced quantitatively with estimates for the magnitude and momentum-space structure of an A1g (s-wave) pairing gap on different Fermi-surface sheets, as well as the identification of the emergent sharp feature as a Bardasis-Schrieffer exciton. Formed as a Cooper-pair bound state in a subdominant dx2-y2 channel, the binding energy of the exciton relative to the gap edge shows that the coupling strength in the subdominant channel is as strong as 60% of that in the dominant s-wave channel. This result suggests that dx2-y2 may be the dominant pairing symmetry in Fe-based superconductors that lack central hole bands.
- Bayerishe Akademie der Wissenshaften (Germany); Technishe Univ. München (Germany); SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Bayerishe Akademie der Wissenshaften (Germany); Technishe Univ., München (Germany)
- Bayerishe Akademie der Wissenshaften (Germany); Technishe Univ. München (Germany)
- Bayerishe Akademie der Wissenshaften (Germany)
- SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., CA (United States). Geballe Lab. for Advanced Materials.
- Univ. of California, Santa Barbara, CA (United States)
- Nanjing Univ. (China). National Lab. of Solid State Microstructures.
- Publication Date:
- OSTI Identifier:
- Grant/Contract Number:
- HA 2071/7; A5; AC02-76SF00515
- Accepted Manuscript
- Journal Name:
- Physical Review. X
- Additional Journal Information:
- Journal Volume: 4; Journal Issue: 4; Journal ID: ISSN 2160-3308
- American Physical Society
- Research Org:
- SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
- Sponsoring Org:
- USDOE Office of Science (SC)
- Country of Publication:
- United States
- 36 MATERIALS SCIENCE
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