Evidence for two superconducting gaps in MgB2.
We have measured the Raman spectra of polycrystalline MgB2 from 25 to 1200 cm(-1). A superconductivity-induced redistribution in the electronic Raman continuum was observed. Two pair-breaking peaks appear in the spectra, suggesting the presence of two superconducting gaps. The measured spectra were analyzed using a quasi-two-dimensional model in which two s-wave superconducting gaps open on two sheets of Fermi surface. For the gap values we have obtained Delta(1) = 22 cm(-1) ( 2.7 meV) and Delta(2) = 50 cm(-1) ( 6.2 meV). Our results suggest that a conventional phonon-mediated pairing mechanism occurs in the planar boron sigma bands and is responsible for the superconductivity of MgB2.
Chen
X K
XK
Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6.
Konstantinovic
M J
MJ
Irwin
J C
JC
Lawrie
D D
DD
Franck
J P
JP