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Title: Evidence of superconductivity-induced phonon spectra renormalization in alkali-doped iron selenides

Polarized Raman scattering spectra of superconducting K xFe 2-ySe 2 and nonsuperconducting K 0.8Fe 1.8Co 0.2Se 2 single crystals were measured in a temperature range from 10 K up to 300 K. Two Raman active modes from the I4/mmm phase and seven from the I4/m phase are observed in frequency range from 150 to 325 cm -1 in both compounds, suggesting that K 0.8Fe 1.8Co 0.2Se 2 single crystal also has two-phase nature. Temperature dependence of Raman mode energy is analyzed in terms of lattice thermal expansion and phonon-phonon interaction. Temperature dependence of Raman mode linewidth is considered as temperature-induced anharmonic effects. It is shown that change of Raman mode energy with temperature is dominantly driven by thermal expansion of the crystal lattice. Abrupt change of the A 1g mode energy near T C was observed in K xFe 2-ySe 2 , whereas it is absent in K 0.8Fe 1.8Co 0.2Se 2. Phonon energy hardening at low temperatures in the superconducting sample is a consequence of superconductivity-induced redistribution of the electronic states below critical temperature.
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [2] ;  [1]
  1. Univ. of Belgrade, Belgrade (Serbia). Institute of Physics Belgrade
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). Condensed Matter Physics and Materials Science Dept.; Stony Brook Univ., NY (United States). Dept. of Physics and Astronomy
  3. Brookhaven National Lab. (BNL), Upton, NY (United States). Condensed Matter Physics and Materials Science Dept.
Publication Date:
Report Number(s):
BNL-111746-2016-JA
Journal ID: ISSN 0953-8984; R&D Project: PM016; KC0201050
Grant/Contract Number:
SC00112704; Ac02-98CH10886
Type:
Accepted Manuscript
Journal Name:
Journal of Physics. Condensed Matter
Additional Journal Information:
Journal Volume: 27; Journal Issue: 48; Journal ID: ISSN 0953-8984
Publisher:
IOP Publishing
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:
1240587