The Taming of the Silkworm: Silkworms, Bombyx mori , represent one of the few domesticated insects, having been domesticated over 10,000 years ago. Xia et al. (p. 433 , published online 27 August) sequenced 29 domestic and 11 wild silkworm lines and identified genes that were most likely to be selected during domestication. These genes represent those that enhance silk production, reproduction, and growth. Furthermore, silkworms were probably only domesticated once from a large progenitor population, rather than on multiple occasions, as has been observed for other domesticated animals.

Low-temperature magnetic sensors are based on Hall effect in thin metallic films. Their sensitivity is more than one order of magnitude smaller than silicon-based Hall sensors operating at room-temperature, because so is the Hall effect in metals. Besides, in order to avoid significant Joule heating, only very small bias currents can be injected. Here we show that a sensor based on photo-induced Hall effect, in which charge is photo-generated in a semiconductor and injected into an adjacent metallic layer, can be used as a bias-free, cryogenic sensor. The system consists of a platinum thin-film deposited on intrinsic-silicon substrate. The film forms a Schottky interface with the semiconductor. At room temperature, carriers photo-generated in the semiconductor are injected into the metal because of rounding-off of the Schottky barrier and deflected by a magnetic field applied in the film-plane. At cryogenic temperature and well-below the freeze-out temperature for silicon, the photo-generated electrons can tunnel through the barrier and the sensor recovers the same sensitivity as that observed at room temperature.

The Hall effect exists in metals, where the low resistance to electrical current would make Joule heating be negligible. We engineered a system in which the Hall effect in a metal is greatly enhanced and Joule heating suppressed. The device recovers tunable sensitivity, without compromising linearity, by replacing current bias with light bias. Our system consists of an extended metal/semiconductor junction, where the metal is highly transparent to light and forms a Schottky interface with the semiconductor.