Abstract
We report NMR studies that address the underlying two superconducting (SC) gaps model and a possible mechanism for interpreting a high SC transition temperature of in a recently discovered We reported in a previous paper [Phys. Rev. Lett. 127001 (2001)] that the results of the nuclear-spin-lattice relaxation rate, in the SC state revealed the existence of a single large SC gap with This conclusion is corroborated by the calculation that any two-gap models cannot account for the experimental results. In Al-doped the result of in the SC state revealed that a size in the SC gap is not changed by substituting Al for Mg. The reduction in by Al doping is shown to be due to the decrease of the density of states at the Fermi level. According to the McMillan equation, an experimental relation between and the relative change in allowed us to estimate a characteristic phonon frequency and an electron-phonon coupling constant These results suggest that the high- superconductivity in is mediated by the strong electron-phonon coupling with high-frequency phonons.
- Received 11 January 2002
DOI:https://doi.org/10.1103/PhysRevB.66.064516
©2002 American Physical Society