Observation of non-classical rotational inertia in bulk solid 4He
Motoshi Kondo, Shunichi Takada, Yoshiyuki Shibayama, Keiya Shirahama
TL;DR
This paper reports the first experimental confirmation of non-classical rotational inertia in bulk solid helium-4, indicating potential supersolid behavior, with observed NCRI fractions below 200 mK in cylindrical samples.
Contribution
It provides the first direct experimental evidence of NCRI in bulk solid 4He, supporting the existence of a supersolid phase.
Findings
NCRI observed below 200 mK in bulk solid 4He
NCRI fraction at 70 mK is 0.14%
Results confirm prior supersolid indications by Kim and Chan
Abstract
In recent torsional oscillator experiments by Kim and Chan (KC), a decrease of rotational inertia has been observed in solid 4He in porous materials and in a bulk annular channel. This observation strongly suggests the existence of "non-classical rotational inertia" (NCRI), i.e. superflow, in solid 4He. In order to study such a possible "supersolid" phase, we perform torsional oscillator experiments for cylindrical solid 4He samples. We have observed decreases of rotational inertia below 200 mK for two solid samples (pressures P = 4.1 and 3.0 MPa). The observed NCRI fraction at 70 mK is 0.14 %, which is about 1/3 of the fraction observed in the annulus by KC. Our observation is the first experimental confirmation of the possible supersolid finding by KC.
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