Plate Nº 77 · recorded October 10, 2026
PhysicsReported finding
Two Superconducting Orders Hiding Inside Ultrathin Films
Israeli physicists report that niobium diselenide and tantalum disulfide, two well-studied ultrathin superconductors, each contain two interacting superconducting orders appearing as one.
By Elena Vasquez3 min read614 words
In brief
- Published August 31, 2026, in Physical Review Letters, vol. 137, no. 1, DOI 10.1103/p836-tdgw.
- Two materials studied: ultrathin flakes of niobium diselenide (NbSe2) and tantalum disulfide (TaS2).
- Each material contains two interacting superconducting orders, not one as long assumed.
- Bulk niobium diselenide may harbor three interacting superconducting orders.
- Led by PhD student Shahar Simon and MSc student Maya Klang under Profs. Oded Millo and Hadar Steinberg of the Hebrew University of Jerusalem.
Two superconductors long thought to contain a single quantum behavior each hide two distinct superconducting states working in tandem, physicists at the Hebrew University of Jerusalem report in the August 31, 2026, issue of Physical Review Letters.
The finding concerns ultrathin flakes of niobium diselenide (NbSe2) and tantalum disulfide (TaS2). For years, both materials seemed to carry current with a single energy gap, a key measure of how electrons form pairs and travel without electrical resistance. Highly sensitive tunneling spectroscopy now reveals that each contains two superconducting "orders" interacting so strongly they masquerade as one.
"It's a bit like listening to what sounds like a single singer, only to discover it's actually a perfectly synchronized duet," the researchers said.
How did the team find the hidden states?
The group, led by PhD student Shahar Simon and MSc student Maya Klang, used scanning tunneling spectroscopy to probe few-layer samples only a few atoms thick. Prof. Oded Millo and Prof. Hadar Steinberg, both of the Racah Institute of Physics and the Center for Nanoscience and Nanotechnology at Hebrew University, supervised the work.
Models built around a single superconducting order failed to reproduce the detailed shape of the energy spectrum reported in earlier experiments. When the researchers applied a more advanced model containing two distinct orders, the data fell into line. The same approach also captured the materials' response to applied magnetic fields.
What does "two superconducting orders" actually mean?
In a conventional superconductor, electrons pair into a single collective state once the temperature drops below a critical threshold. The energy gap measures how tightly those pairs bind. Niobium diselenide, one of the most studied ultrathin materials in condensed-matter research, has long appeared to follow this textbook picture.
The new measurements suggest that picture is incomplete. Each ultrathin material supports two separate pairing channels that couple to each other. Together they produce a combined spectroscopic signal that earlier, less sensitive instruments could not resolve.
What did the study find for thicker samples?
The authors also examined bulk-like forms of niobium diselenide, made of many atomic layers rather than a few. Their analysis points to three interacting superconducting orders in that case. The result hints that superconductivity in this material family grows more intricate as the number of layers rises.
That added complexity could matter for future devices. Superconductors already appear in medical imaging systems such as MRI machines, and they are also seen as candidate hardware for ultra-efficient power transmission and quantum computers. Knowing precisely how electrons organize inside these materials would let engineers tune them more deliberately.
Why did earlier work miss the second state?
Previous studies relied on measurements that averaged over the electronic structure, blurring signals from different pairing channels. The Jerusalem team used a metallic tip pressed against the surface, which reads out the local density of electronic states with high energy resolution. The sharper sensitivity made the weaker second order visible.
Traditional theories had also struggled to reproduce the exact shape of the superconducting spectrum earlier experiments on NbSe2 reported. A two-band model resolves that long-standing discrepancy, the researchers argue.
What remains uncertain?
The study relies on spectroscopic measurements at low temperatures on exfoliated flakes only a few atoms thick. The authors stop short of claiming that the two-band picture fully explains every reported behavior of these materials. Further measurements will be needed to pin down how the two orders couple in TaS2, where experimental data remain sparser.
The bulk result for NbSe2 is also preliminary, based on indirect signatures rather than a full spectroscopic map. Confirming the three-band picture will likely require similar high-resolution scans on freshly prepared bulk crystals.
via dx.doi.org (Original)
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