Non-classical response from quench-cooled solid helium confined in porous gold

The non-classical rotational inertia (NCRI) in solid helium was detected by a drop in the resonant period of a torsional oscillator. This non-classical response was interpreted as the first possible evidence of supersolidity. A number of subsequent experiments, however, reported unexpected phenomena within the supersolid context. Experimental and theoretical work have drawn attention to the role of disorder in solid helium to explain the inconsistency. We have investigated the non-classical response of solid He-4 confined in porous gold set to torsional oscillation. When solid helium is grown rapidly, nearly 7% of the solid helium appears to be decoupled from the oscillation below about 200 mK. Dissipation appears at temperatures where the decoupling shows maximum variation. In contrast, the decoupling is substantially reduced in slowly grown solid helium. The dynamic response of solid helium was also studied by imposing a sudden increase in the amplitude of oscillation. Extended relaxation in the resonant period shift, suggesting the emergence of the pinning of low-energy excitations, was observed below the onset temperature of the non-classical response. The motion of a dislocation or a glassy solid is restricted in the entangled narrow pores and is not likely responsible for the period shift and long relaxation.