Measurements of Elastic Properties of Langatate at Liquid Helium   Temperatures for design of ultra low loss mechanical systems
  We present full characterisation of acoustic wave devices based on the fully synthetic crystalline material at the liquid helium temperature range { required for the design of ultra low loss mechanical systems in many areas of research including frequency control and fundamental measurements}. Temperature coefficients of the effective elastic tensor of Langatate (LGT) in Lagrangian representation are determined for the temperature range $3.8-15$K. The Lagrangian formalism is mandatory in the analysed situation since the expansion coefficients of the LGT are still unknown at these temperatures. The measurement method involves a set of high-quality resonators of various cut angles, and uses measurements of frequency-temperature relations to extract the temperature coefficients of the elastic tensor. In addition, power sensitivity of LGT resonators at cryogenic temperatures is determined and dominant loss mechanism is identified. 
Maxim Goryachev, Philippe Abbe, Bernard Dulmet, Roger Bourquin and   Serge Galliou
cond-mat.mtrl-sci