In the basement of the laboratory, an 8 tesla magnet hums. Inside it, like a bell in a bell tower, hangs a hollow copper cylinder tuned to a single note. If an axion, a dark matter particle, flies by, the cylinder responds with a faint ring. The trouble is that ordinary copper muffles this ring: at high frequencies, current flows only through a thin skin of the metal, and losses grow. A superconductor would sound cleaner, but in a strong field it is pierced by vortices and loses its properties.

Physicists from the CAPP group found a way to dig a deep moat around the resonator. They took a tape of the high-temperature superconductor REBCO and mechanically peeled it from its rigid substrate, leaving a copper stabilizer 20–100 micrometers thick on the back side. This copper layer became not just a support but a conducting base. The gaps between the resonator segments turned into waveguides below the cutoff frequency, and the radio-frequency field decays in them like a wave in a narrow channel, never reaching the resistive substrate.

To test the idea, they built two resonators. One with a fixed frequency of 5.40 GHz, for record quality. The second, tunable to 2.3 GHz, was integrated into the operating helioscope CAPP-PACE. The first achieved an unloaded quality factor of 1.4×10⁷ in an 8 T field, two orders of magnitude higher than a copper counterpart. The second showed a system noise temperature of 180 millikelvins and a fivefold advantage in quality over copper.

Previously, a high-quality resonator in a strong field was unattainable: copper is limited by the anomalous skin effect, and superconductors are destroyed by vortices. Now, a deep copper moat quenches leakage, and the bell rings clearly even in the hum of the magnet. The technology is ready for dark matter search experiments and can be adapted for accelerator resonators. In the basement of the laboratory, the bell keeps listening, and its ring is becoming ever more distinct.