A thin film of indium arsenide on an insulating substrate behaves like a double-walled thermos: the electrons inside barely give off heat to the surrounding crystal. In an ordinary metal, electrons quickly exchange energy with atomic vibrations, so their temperature is always close to that of the sample. Here, the coupling is so weak that the electron gas can be heated or cooled independently, with almost no energy cost.
Researchers measured this effect using a Josephson junction — a superconducting contact that acts as an ultra-precise thermometer. They found that at temperatures below one kelvin (colder than deep space), electrons remain isolated from the lattice, and superconductivity persists even under strong electric fields. This combination, weak thermal coupling and full electrical controllability, makes the material ideal for thermal circuits, where heat flows are controlled just like currents in ordinary electronics.
The practical payoff lies in single-photon detectors: an absorbed photon slightly warms the electrons, and that tiny temperature blip can be registered with high precision. Such detectors are needed for quantum communication and astronomical observations. Moreover, the platform promises to become the foundation of "caloritronics"—managing heat at the nanoscale, where heat flows not chaotically but directionally, like electricity through wires.
The Josephson junction used as a thermometer is so sensitive that it can detect the heating from a single photon.
In Arthur C. Clarke's novel "The Light of Other Days," ultra-sensitive detectors are mentioned that can catch a single photon from the depths of space: this technology brings such a plot closer to reality.