Transition-edge sensor

A transition edge sensor or TES is a kind of thermistor. It consists of a superconductor, often aluminum or titanium, held right at its critical temperature. If the temperature increases by even a small amount, then the superconducting phase breaks. The sudden rise in resistance can be used to measure the very small changes in temperature. TES arrays are becoming increasingly common in physics and astronomy experiments such as the South Pole Telescope.