We report 11B NMR studies that address the underlying two superconducting (SC) gaps model and a possible mechanism for interpreting a high SC transition temperature (Tc) of ∼40 K in a recently discovered MgB2. We reported in a previous paper [Phys. Rev. Lett. 87, 127001 (2001)] that the results of the nuclear-spin-lattice relaxation rate, 1/T1 in the SC state revealed the existence of a single large SC gap with 2Δ/kBTc∼5. This conclusion is corroborated by the calculation that any two-gap models cannot account for the experimental results. In Al-doped MgB2, the result of 1/T1 in the SC state revealed that a size in the SC gap is not changed by substituting Al for Mg. The reduction in Tc by Al doping is shown to be due to the decrease of the density of states N(EF) at the Fermi level. According to the McMillan equation, an experimental relation between Tc and the relative change in N(EF) allowed us to estimate a characteristic phonon frequency ω ∼700 K and an electron-phonon coupling constani λ∼0.87. These results suggest that the high-Tc superconductivity in MgB2 is mediated by the strong electron-phonon coupling with high-frequency phonons.
|Number of pages||6|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Aug 1 2002|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics