Hidden dual superconducting orders revealed in 2D transition metal dichalcogenides

A team of physicists has identified two strongly coupled superconducting states in ultrathin niobium diselenide (NbSe₂) and tantalum disulfide (TaS₂), materials previously thought to host only a single superconducting energy gap. The discovery emerged from high-resolution tunneling spectroscopy experiments conducted at the Racah Institute of Physics and the Center for Nanoscience and Nanotechnology at the Hebrew University of Jerusalem.

What the measurements revealed

Earlier experimental data on few-layer NbSe₂ suggested a simple, single-energy-gap structure—a hallmark of conventional superconductivity. That apparent simplicity conflicted with theoretical predictions and left unresolved questions about electron pairing mechanisms. Shahar Simon, a Ph.D. student, and Maya Klang, an M.Sc. student, led the investigation under the supervision of Prof. Oded Millo and Prof. Hadar Steinberg. Their work, published in Physical Review Letters on 29 June 2026, shows that the observed single-gap signature arises not from one order parameter, but from two distinct superconducting orders interacting so intensely that standard probes cannot resolve them separately.

The same concealed dual-state behavior was confirmed in TaS₂, a structurally analogous superconductor. “It’s a bit like listening to what sounds like a single singer, only to discover it’s actually a perfectly synchronized duet,” said the researchers.

Why the old model failed

Conventional single-band superconductivity models could not reproduce the precise shape of the measured energy spectra—or explain how the materials responded to applied magnetic fields. The research team instead employed a two-band theoretical framework incorporating strong inter-band coupling. This revised model successfully matched both the spectroscopic data and the magnetic-field-dependent evolution of the gap features.

The agreement between theory and experiment clarifies why prior studies had interpreted the signals as evidence of a single superconducting state: the coupling strength masks the underlying complexity without specialized, high-sensitivity techniques.

Implications for bulk material

The study further indicates that in thicker, bulk forms of NbSe₂, the superconducting structure may involve three interacting orders—not two. This suggests a dimensionality-dependent hierarchy of quantum organization, where reducing thickness does not simplify the system but instead reveals a subset of a richer, multiband ground state.

Accurate characterization of such hidden quantum identities is critical for engineering next-generation devices. Potential applications include components for quantum computers, ultra-efficient electronic circuits, and high-precision sensors—all reliant on precise control over electron pairing and coherence in superconducting materials.

Reference: “Two-Band Superconductivity in Few-Layer NbSe2 and TaS2” by Shahar Simon, Maya Klang, Oded Millo and Hadar Steinberg, 29 June 2026, Physical Review Letters. DOI: 10.1103/p836-tdgw