Evidence for High-frequency Phonon Mediated S-wave Superconductivity : 11B-NMR Study of Al-doped MgB2

Abstract

We report ${}^{11}$B-NMR study on Al-doped MgB${}_2$ that addresses a possible mechanism for a high superconducting (SC) transition temperature ($T_c$) of $\sim 40$ K in recently discovered MgB${}_2$. The result of nuclear spin lattice relaxation rate $1/T_1$ in the SC state revealed that the size in the SC gap is not changed by substituting Al for Mg. The reduction on $T_c$ by Al-doping is shown to be due to the decrease of $N(E_F)$. According to the McMillan equation, the experimental relation between $T_c$ and the relative change in $N(E_F)$ allowed us to estimate a characteristic phonon frequency $\omega \sim 700$ K and an electron-phonon coupling constant $\lambda \sim 0.87$. These results suggest that the high-$T_c$ superconductivity in MgB${}_2$ is mediated by the strong electron-phonon coupling with high-frequency phonons.

6pages, 3figures

Cited by in corpus (8)

• Specific heat of single crystal MgB_2: a two-band superconductor with two different anisotropies
• Scanning Tunneling Spectroscopy in MgB 2
• ${}^{11}$B and ${}^{27}$Al NMR spin-lattice relaxation and Knight shift study of Mg${}_{1-x}$Al${}_x$B${}_2$. Evidence for anisotropic Fermi surface
• Antiferromagnetic Spin Fluctuations and Unconventional Nodeless Superconductivity in an Iron-based New Superconductor (Ca_4Al_2O_{6-y})(Fe_2As_2):75As-NQR Study
• Effect of disorder on the NMR relaxation rate in two-band superconductors
• NMR relaxation time in a clean two-band superconductor
• ${}^{11}$B NMR study of pure and lightly carbon doped MgB${}_2$ superconductors
• Pressure evolution of the normal- and superconducting-state properties of the line-nodal material CaSb${}_2$ revealed by ${}^{123}$Sb nuclear quadrupole resonance