High Pressure Triples Superconducting Temperature in Tantalum Disulfide
Applying intense pressure to tantalum disulfide raises its superconducting temperature threefold and boosts electron participation sevenfold, revealing new insights into unconventional superconductivity.
Tantalum disulfide doesn’t normally attract much attention outside a niche corner of condensed-matter physics, but under enough pressure, its behavior becomes hard to ignore. Researchers at the Paul Scherrer Institute have now shown that applying high pressure to the quantum material tantalum disulfide causes it to become superconducting at temperatures roughly three times higher than under ambient conditions, with the number of electrons taking part in the superconducting condensate increasing sevenfold. The finding, published in Nature Communications, pushes against the usual understanding of how electrons pair up in so-called unconventional superconductors.
The team used muon spin spectroscopy to demonstrate that high pressure makes tantalum disulfide superconducting in all three spatial dimensions — a departure from its ambient-pressure behavior, where the superconducting state is essentially two-dimensional. That change in dimensionality is tied to the large jump in participating electrons: under ambient conditions, only a thin layer of electrons near the surface contributes, but pressure forces the material’s layers closer together, allowing electrons from deeper within the crystal structure to join the superconducting state.
This isn’t just a matter of turning up a dial and watching a known effect scale up. Tantalum disulfide is a charge-density-wave material, where electron density spontaneously modulates, and its superconductivity is believed to be mediated by something other than the simple electron-phonon coupling that explains conventional superconductors. The fact that pressure can so dramatically increase both the critical temperature and the fraction of electrons involved suggests that the charge-density-wave order and the superconductivity are competing, and that suppressing one liberates the other in a way that wasn’t obvious before.
Pressure, as an experimental tool, has the advantage of being clean: it doesn’t introduce chemical impurities or lattice defects the way doping does, so what you measure is intrinsic to the material’s electronic structure. That makes tantalum disulfide a particularly useful case study for understanding the broader class of unconventional superconductors, which include the cuprates and iron-based materials that have kept physicists busy for decades.
It’s still a long way from a room-temperature superconductor, of course. The absolute temperatures involved remain cryogenic, and the pressures required — gigapascal-range, comparable to those deep inside the Earth — are not practical for applications. But the point of this kind of work isn’t immediate engineering; it’s to reveal what the electrons are actually doing. Getting a sevenfold increase in participation into the superconducting state, and doing it by simply squeezing a crystal, makes that picture considerably clearer than it was before.