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Title: Anomalous phonon behavior in superconducting CaKFe 4 As 4 : An optical study

Here, the temperature dependence of ab-plane optical conductivity of CaKFe 4As 4 has been measured below and above its superconducting transition temperature T c≃35.5 K. In the normal state, analysis with the two-Drude model reveals a T-linear scattering rate for the coherent response, which suggests strong spin-fluctuation scattering. Below the superconducting transition, the optical conductivity below 120 cm –1 vanishes, indicating nodeless gap(s). The Mattis-Bardeen fitting in the superconducting state gives two gaps of Δ 1 ≃ 9 meV and Δ 2 ≃ 14 meV, in good agreement with recent angle-resolved photoemission spectroscopy (ARPES) results. In addition, around 255 cm –1, we observe two different infrared-active Fe-As modes with obvious asymmetric lineshape, originating from strong coupling between lattice vibrations and spin or charge excitations. Considering a moderate Hund's rule coupling determined from spectral weight analysis, we propose that the strong fluctuations induced by the coupling between itinerant carriers and local moments may affect the phonon mode, and the electron-phonon coupling through the spin channel is likely to play an important role in the unconventional pairing in iron-based superconductors.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [4] ;  [2] ;  [5]
  1. Chinese Academy of Sciences (CAS), Beijing (China); Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
  3. Center for High Pressure Science and Technology Advanced Research, Beijing (China)
  4. Chinese Academy of Sciences (CAS), Beijing (China)
  5. Chinese Academy of Sciences (CAS), Beijing (China); Collaborative Innovation Center of Quantum Matter, Beijing (China)
Publication Date:
Report Number(s):
BNL-113510-2017-JA
Journal ID: ISSN 2469-9950; PRBMDO; R&D Project: PO016; KC0202020; TRN: US1700873
Grant/Contract Number:
SC00112704; SC0012704
Type:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 95; Journal Issue: 6; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (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
OSTI Identifier:
1345727
Alternate Identifier(s):
OSTI ID: 1343337