Casimir force measurements between metal and high-$T_c$ superconductor surfaces

It is well known that the strength of the Casimir force between two objects is controlled by the dielectric properties (or optical conductivity) of the objects. Nearly all precision measurements of Casimir forces to date are between two metals. Here we report measurements of the Casimir force between a metal-coated sphere and a plate made of the high-$T_c$ cuprate superconductor BSCCO-2212, using an atomic force microscope at room temperature. BSCCO has dielectric properties substantially different from metals and indeed most materials, displaying extreme anisotropy in dc and optical conductivity, as well as a ``strange metal'' normal state. The force between metal and BSCCO is compared to the force measured between two metals.