Tunneling with very long relaxation times in glasses, organic materials, and Nb-Ti-H (D)

Abstract

The long-time (t=10–200 h) heat release $$\dot Q$$ from glasses, from organic materials, and from Nb-Ti-H (D) was measured at 30≤T≤70 mK. For Suprasil W glass, Dimethyl-Siloxan, Stycast 1266, Stycast 2850 FT, Vespel, and for Nb-Ti-H (D) with various Ti and D concentrations, we found $$\dot Q \sim t^{ - 1}$$ . Typical values are $$\dot Q$$ = 0.05 nW/g for the organic materials and for Nb-Ti-H (D) and $$\dot Q$$ = 0.005 nW/g for the glass att=100 h after cooldown from room temperature. For charging temperaturesT i <5 K, we find the predicted dependence $$\dot Q \sim t_i^2$$ (investigated for Suprasil W glass and for Nb-Ti-D). The observed time and temperature dependences agree with predictions of the conventional two-level tunneling model for amorphous materials even at these very long times. No heat release was observed for Teflon, graphite, and Al2O3.