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Two-Band Superconductivity in Few-Layer NbSe_{2} and TaS_{2}
Shahar Simon1, Maya Klang1, Oded Millo1
1The Hebrew University of Jerusalem, The Racah Institute of Physics, Jerusalem 91904, Israel and The Center for Nanoscience and Nanotechnology, Hebrew University, Jerusalem 91904, Israel.
Physical Review Letters
|July 23, 2026
Summary
Superconductivity in ultrathin transition metal dichalcogenides like 2H-NbSe2 and 2H-TaS2 is explained by a two-band model. This model accurately describes tunneling data and magnetic field effects, even when a single gap appears.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Superconductivity
Background:
- The nature of superconductivity in ultrathin transition metal dichalcogenides (TMDs) remains unclear.
- Single-band theories fail to explain observed tunneling data in 2H-NbSe2 and 2H-TaS2.
Purpose of the Study:
- To investigate the superconducting properties of ultrathin 2H-NbSe2 and 2H-TaS2.
- To determine the appropriate theoretical model for superconductivity in these materials.
Main Methods:
- Tunneling measurements on thin exfoliated samples of 2H-NbSe2 and 2H-TaS2.
- Analysis using the McMillan two-band model of superconductivity.
- Quantitative analysis of magnetic field-induced pair breaking.
Main Results:
- Tunneling data shows excellent agreement with the McMillan two-band model, even with apparent single gaps.
- The model holds true for large scattering parameters relative to superconducting gaps.
- Magnetic pair breaking is also well-described by the two-band theory.
Conclusions:
- Ultrathin 2H-NbSe2 and 2H-TaS2 superconductivity is best explained by a two-band model, with gaps on the Γ and K Fermi surfaces.
- Bulk 2H-NbSe2 is likely a three-band superconductor based on these findings.
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