Thermal conduction across copper-lead-copper sandwiches at helium temperatures

Measurements have been made of the thermal conductance of copper-lead-copper sandwiches between 1.3 and 4.0 °K. For the lead in the normal state the conductance is thought to be predominantly electronic, but in the superconducting state two specimens showed behaviour characteristic of phonon flow ( T 3 temperature dependence), while in another the conductance was smaller and varied more rapidly with temperature ( T 5 7 ). The results have been discussed in terms of theoretical models proposed by Little in 1959 for phonon flow across an interface and by Strässler and Wyder in 1963 for electron flow. The conductance of one sandwich at 1.35 °K increased by a factor of 105 when the lead was driven normal by application of a magnetic field but showed no further change in conductance in fields up to 5 kOe. These properties may have some application in thermal switches. The paper also describes measurements on copper sandwiches containing Wood's metal and an epoxy resin (Araldite AY103).