Abstract
We have measured the reflectivity of the optimally doped single crystal over the broad frequency range from to 12 and for temperatures from 8 K to 300 K. The optical conductivity spectra of the low-frequency region in the normal state (80 K K) is well fitted with two Drude forms, which indicates the presence of multiple bands at the Fermi level. Decreasing temperature below 80 K, this low-frequency Drude spectra develops a pseudogap (PG) hump structure at around and continuously evolves into the fully opened superconducting (SC) gap structure below . Theoretical calculations of the optical conductivity with the preformed Cooper pair model provide an excellent description of the temperature evolution of the PG structure above into the SC gap structure below . The extracted two SC gap sizes are and , suggesting as a multiple-gap superconductor with a mixed character of the weak-coupling and strong-coupling superconductivity.
3 More- Received 30 November 2016
- Revised 28 February 2017
DOI:https://doi.org/10.1103/PhysRevB.95.094510
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