Narayan Budhathoki

Growing an ultra-pure germanium crystal is a bit like baking a finicky soufflé: a slight overheating or an extra speck of impurity, and the whole ingot is only good for remelting. Such crystals are the heart of detectors that catch the rarest events, from dark matter to double beta decay.

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.