Kinetic inductance in superconducting CoSi${}_2$ coplanar microwave transmission lines

Abstract

We have looked into cobalt disilicide (CoSi${}_2$) as a potential building block for superconducting quantum circuits. In order to achieve this, we annealed a thin layer of Co to create 10-105 nm thick microwave cavities from CoSi${}_2$ embedded in the silicon substrate. The cavity properties were measured as a function of temperature and power. In films measuring 10 and 25 nm, we find a significant kinetic inductance $L_{\mathrm{K}}$ with a non-BCS power-law variation $\delta L_{\mathrm{K}}\propto T^{4.3\pm 0.2}$ at low temperatures. The quality factor of the studied microwave resonances increased almost linearly with thickness, with two-level systems having very little effect. The power dependence of kinetic inductance was analyzed in terms of heat flow due to electron-phonon coupling, which was found stronger than estimated for heat relaxation by regular quasiparticles.

7 pages, 4 figures