Near-field heat transfer across a gap between plane-parallel tungsten layers in vacuo was studied experimentally with the temperature of the cold sample near 5 K and the temperature of the hot sample in the range 10–40 K as a function of the gap size $d$. At gaps smaller than one-third of the peak wavelength ${\lambda }_m$ given by Wien’s displacement law, the near-field effect was observed. In comparison with blackbody radiation, hundred times higher values of heat flux were achieved at $d\approx 1\mu \mathrm{m}$. Heat flux normalized to the radiative power transferred between black surfaces showed scaling $({\lambda }_m/d{)}^n$, where $n\approx 2.6$. This Letter describes the results of experiment and a comparison with present theory over 4 orders of magnitude of heat flux.

• Received 8 February 2012

DOI:https://doi.org/10.1103/PhysRevLett.109.224302