Momentum-dependent multiple gaps in magnesium diboride probed by electron tunnelling spectroscopy

Area of Science:

• Condensed matter physics
• Materials science
• Superconductivity research

Background:

• The energy gap is a critical property of superconductors.
• Magnesium Diboride (MgB2) is a superconductor known for its two distinct superconducting gaps due to electron-phonon interactions in multiple bands.
• Theoretical models predict anisotropic gap variations across MgB2's Fermi surface, but experimental evidence has been lacking.

Purpose of the Study:

• To experimentally investigate the predicted anisotropic energy gap distribution in MgB2.
• To provide experimental validation for theories of multi-band superconductivity in MgB2.
• To explore the role of anisotropic electron-phonon interactions in MgB2's superconducting properties.

Main Methods:

• Fabrication of MgB2/native oxide/Pb tunnel junctions.
• Utilizing electron tunneling spectroscopy to probe superconducting energy gaps.
• Analyzing the distribution of measured gap values.

Main Results:

• Direct experimental observation of a distribution of superconducting gap values in MgB2.
• Confirmation that a single or two gap values are insufficient to describe real MgB2 samples.
• Evidence supporting the significant influence of anisotropic electron-phonon interactions.

Conclusions:

• The experimental results confirm the anisotropic nature of superconductivity in MgB2.
• The observed gap distribution provides crucial data for refining theoretical models of multi-band superconductors.
• This study highlights the importance of considering anisotropic interactions in understanding MgB2 superconductivity.