EMP is funded through the Horizon2020 programme of the European Commission.
Selected Publications

Elastic measurements of amorphous silicon films at mK temperatures

A. Fefferman, A. Maldonado, E. Collin, X. Liu, T. Metcalf and G. Jernigan

The low-temperature properties of glass are distinct from those of crystals due to the presence of poorly understood low-energy excitations. The tunneling model proposes that these are atoms tunneling between nearby equilibria, forming tunneling two-level systems (TLSs). This model is rather successful, but it does not explain the remarkably universal value of the mechanical dissipation Q1 near 1 K. The only known exceptions to this universality are the Q1 of certain thin films of amorphous silicon, carbon and germanium. Recently, it was found that Q1 of amorphous silicon (a-Si) films can be reduced by two orders of magnitude by increasing the temperature of the substrate during deposition. According to the tunneling model, the reduction in Q1 at 1 K implies a reduction in P0γ2, where P0 is the density of TLSs and γ is their coupling to phonons. In this preliminary report, we demonstrate elastic measurements of a-Si films down to 20 mK. This will allow us, in future work, to determine whether P0 or γ is responsible for the reduction in Q1 with deposition temperature.

J. Low Temp. Phys. 187 (2017) 654

doi: 10.1007/s10909-016-1686-6