If a conducting wire is sufficiently narrow, the electrical conductance through it is quantized, increasing in steps of 2e2/h with the width of the wire. Does an analogous quantization apply to another type of transport—the conduction of heat by phonons? The theoretical answer is “yes.” A narrow, thermally insulating wire should be able to carry no more heat per mode than g0 = π2k2T/3h, where k is Boltz‐mann's constant, T is the temperature and h is Planck's constant.

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