A New Window into Atom-Thin Superconductors
Stacks of 2D materials are becoming a leading platform for exploring exotic superconducting states. But progress has been hampered by a difficulty in measuring a fundamental property of these systems, known as superfluid phase stiffness. This property quantifies how strongly a superconductor resists changes to the quantum phase of its superconducting state. Now researchers in the US and Japan have demonstrated a way to reveal the superfluid stiffness of a broad class of atomically thin superconductors [1].
In the technique, a sample of the material and a superconducting microwave resonator are placed next to each other on a chip. The resonator’s electromagnetic field interacts with the sample via an effect called capacitive coupling, and the sample’s superfluid stiffness can be inferred from its response to the field. Unlike previous approaches, this one requires no electrical contact with the sample. This feature simplifies the fabrication process and avoids complications that can distort the superfluid-stiffness measurement, such as contact electrical resistance and superconducting proximity effects.
The researchers demonstrated their method using the atomically thin material 4Hb-TaS2, which is composed of alternating layers of two different TaS2 crystal structures. There is ongoing debate over this material’s superconducting energy gap—the energy required to break apart the electron pairs responsible for superconductivity. Specifically, some reports have suggested the presence of nodes—points in momentum space where this energy gap vanishes. The team’s new temperature-dependent measurements of this material’s superfluid stiffness provide strong evidence against the existence of such nodes.
–Ryan Wilkinson
Ryan Wilkinson is a Corresponding Editor for Physics Magazine based in Durham, UK
References
- T. Chistolini et al., “Contactless cavity sensing of superfluid stiffness in atomically thin 4Hb-TaS2,” Phys. Rev. Lett. 137, 076002 (2026).