Shasika Panamaldeniya

An ordinary piece of germanium the size of your palm can spot a single dark matter particle flying through it. But for that, the crystal must be nearly perfect: free of electrical noise, with a uniform internal field, and contacts that don't spark at high voltage. In the new work, they assembled the KL01 detector.

In an ultra-pure germanium crystal cooled to near absolute zero, a single electron can trigger a whole avalanche of charges, like a small pebble dislodged from a slope that sweeps down a stream of snow. Such internal signal amplification is a dream for detectors of dark matter or rare decays.

To catch a whisper in a noisy room, you need a highly sensitive microphone that barely makes noise itself. In the physics of rare events, that role is played by detectors made of ultra-pure germanium — a semiconductor crystal that turns a passing particle into a tiny electrical pulse.