Anomalous response of ⁴He confined in nanoporous media to torsional oscillation

The existence of "Non-Classical Rotational Inertia (NCRI)" in solid ⁴He below 0.2 K has been controversial and interpreted by a number of different theories. We report on torsional oscillator measurements for ⁴He in a nanoporous Gelsil glass, which has a network of nanopores with 3.5 nm in diameter. In addition to the usual "low-T NCRI" with an onset temperature 0.15 K, we find a larger decrease in rotational moment of inertia in a broad range of temperature from 0.2 to 1.9 K. This "high-T inertial anomaly" is accompanied with multiple dissipation peaks, but has no dependence on torsional oscillation velocity unlike the low-T NCRI. Since the high-T anomaly is observed also in confined liquid states, it originates in amorphous solid ⁴He layer near the pore wall. Our result shows that different types of supersolid - like phenomena, i.e. inertial anomalies, can coexist in a single ⁴He sample, even with genuine superfluidity of liquid ⁴He.