Wires Luis G. C. Rego and George Kirczenow Phys. Under the right conditions it cannot have just any value, but comes only in units of the universal conductance quantum. In the past year, researchers have discovered that a similar quantization should occur for the conduction of heat. In the 6 July PRL a pair of theorists puts this concept on an even firmer footing by showing that it should be observable in practical experiments.
Heat flow in a small wire.
Just as light waves can be described as collections of photons, the vibrations of a crystal lattice can be analyzed in terms of phonons, which can travel through a material, transporting energy in the form of heat. The existence of the thermal quantum was deduced implicitly last year by Michael Roukes, of the California Institute of Technology, and his colleagues, but Rego and Kirczenow go on to analyze how an experiment could observe it. One difficulty in observing the quantization of heat conduction experimentally is the effect of phonons reflecting from the points where the wire connects to the heat reservoir at each end. Rego and Kirczenow show that for a wire with square cross-section, these effects are minimized if the connection is extremely smooth. Ohm-meter for heat.