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.