The thermal conductance of indium-filled contacts at cryogenic temperatures

Indium foil is often used to increase the thermal contact conductance h _c of junctions at cryogenic temperatures, yet relatively few experimental data on h _c at subambient temperatures are available. Here, experimental measurements of h _c at a copper/copper junction containing a 25.4-μm-thick indium foil are reported. The average sample temperature ranged from 40 to 180 K, and the contact pressures ranged from 0.2 to 20 MPa. Although it was originally anticipated that increasing the contact pressure would lead to increasing h _c, the observed h _c showed little or no dependence on contact pressure. This was attributed to the severe nonflatness of the copper surfaces. Comparison between the measured h _c, and that calculated from existing "flat" and "nonflat" theories indicated better agreement with the "nonflat" model, although the model still predicted that h _c should depend on pressure.