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Evidence for two superconducting gaps in MgB2
X K Chen1, M J Konstantinovic, J C Irwin
1Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6.
Physical Review Letters
|October 3, 2001
Summary
Raman spectra of magnesium diboride (MgB2) reveal two superconducting gaps, indicating a phonon-mediated pairing mechanism in the boron sigma bands. This finding clarifies the electronic structure responsible for MgB2 superconductivity.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Superconductivity
Background:
- Magnesium diboride (MgB2) is a superconductor with a complex electronic structure.
- Understanding the pairing mechanism is crucial for advancing superconductor technology.
Purpose of the Study:
- To investigate the superconducting properties of MgB2 using Raman spectroscopy.
- To identify the number and nature of superconducting gaps in MgB2.
- To elucidate the underlying mechanism responsible for MgB2 superconductivity.
Main Methods:
- Measurement of Raman spectra of polycrystalline MgB2 over a wide frequency range (25–1200 cm(-1)).
- Analysis of spectral changes associated with superconductivity.
- Application of a quasi-two-dimensional model to interpret the superconducting gaps.
Main Results:
- Observed a superconductivity-induced redistribution in the electronic Raman continuum.
- Identified two distinct pair-breaking peaks, suggesting two superconducting gaps.
- Determined the values of the two s-wave superconducting gaps: Δ(1) = 22 cm(-1) (2.7 meV) and Δ(2) = 50 cm(-1) (6.2 meV).
Conclusions:
- The results strongly suggest the presence of two superconducting gaps in MgB2.
- A conventional phonon-mediated pairing mechanism is proposed to be responsible for superconductivity, specifically within the planar boron sigma bands.