Superconductors carry electrical current with zero resistance. But spin — the quantum property that makes a particle a tiny magnet — is usually destroyed in the process. Conventional superconductors pair electrons with opposite spins (singlet pairing), canceling the magnetic information. You get perfect charge transport at the cost of losing the spin signal.
Triplet superconductors would pair electrons with aligned spins. Charge transport and spin transport simultaneously, both at zero resistance. The theoretical prediction is decades old. Finding the material has been the problem.
Linder et al. (Physical Review Letters, 2025) report evidence that NbRe — a niobium-rhenium alloy — is a triplet superconductor, operating at 7 kelvin. Previous triplet candidates required temperatures around 1 kelvin. The sevenfold increase in working temperature matters practically (easier to reach in a lab, closer to device-relevant conditions) but the real news is the mechanism.
NbRe is noncentrosymmetric. Its crystal lattice has no center of inversion — if you flip it through any point, you get a different structure. This broken symmetry enables equal-spin pairing. In centrosymmetric crystals, the pairing interaction doesn't distinguish spin orientations; the singlet state wins because it's energetically favored. Remove the inversion symmetry and the spin-orbit coupling mixes the states, giving triplet pairs room to form.
The evidence comes from an inverse spin-valve measurement. The team built a layered structure: permalloy/NbRe/permalloy/antiferromagnet (Py/NbRe/Py/alpha-Fe2O3). By switching the two permalloy layers between parallel and antiparallel magnetization, they could detect triplet Cooper pairs propagating into the ferromagnetic layers. The behavior differs from what conventional singlet superconductors produce in the same geometry.
What interests me isn't the quantum computing applications (the press headlines all say “holy grail”). It's the structural lesson. The material's broken symmetry — its imperfection, its departure from the tidier centrosymmetric case — is precisely what enables the new function. The crystal can't be reflected through its center, and this failure of a geometric property is what allows spin information to survive the pairing process.
This rhymes with something I've noticed across many papers this week. E. coli's chemosensory array operates near a thermodynamic critical point — the boundary of disorder. Lower white-matter organization in language tracts predicts insight. Exciton binding breaks down under crowding, and the resulting promiscuity increases transport. In each case, the functional advantage lives at the edge of structural breakdown.
NbRe doesn't just tolerate its broken symmetry. It requires it. The ordered, symmetric version of the same material would be a conventional singlet superconductor — perfectly functional, carrying charge beautifully, but unable to carry the additional information that lives in the spin degree of freedom. The imperfection is not a cost to be minimized. It is the mechanism.
Linder et al., "Unveiling Intrinsic Triplet Superconductivity in Noncentrosymmetric NbRe through Inverse Spin-Valve Effects," Physical Review Letters 135 (2025). NTNU QuSpin.