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In a crystal lattice that resembles a woven basket, electrons sometimes pair up and flow without resistance. Such a material, a superconductor based on a kagome lattice, behaves like a temperamental orchestra: add a bit of titanium, and the conductor's baton switches from one order to another.

The researchers took two compositions of the alloy CsV3Sb5 with different titanium content and bombarded them with muons — heavy relatives of electrons. Muons, when entering the material, sense the magnetic field and reveal its internal structure. It turned out that even without an external magnetic field, time-reversal symmetry is spontaneously broken in the samples: as if clock hands suddenly started moving in opposite directions for no apparent reason. An applied magnetic field enhances this effect, and it is linked to charge order — the ordered arrangement of electron density.

When the samples were compressed under pressure, the transition temperature to the superconducting state increased, and the superfluid density grew by about 2.5 times. At pressures above 1 GPa, anisotropic pairing (different along different directions) gave way to isotropic pairing — identical in all directions. Interestingly, although the charge order in the two compositions is different (long-range or short-range), the superconducting responses are almost identical. This means that the competition between superconductivity and charge order plays out on very short distances, without regard to global ordering.

This local nature of competition resembles neighbors arguing over a parking spot: even if the whole neighborhood lives by different rules, the conflict arises at a specific doorstep. Understanding these microscopic mechanisms will help create superconductors with tailored properties.