Probing the Upper Limit of Nonclassical Rotational Inertia

TL;DR

This study investigates how geometric confinement affects the nonclassical rotational inertia (NCRI) in solid helium-4, revealing a maximum NCRI at specific widths and demonstrating the nonlocal nature of supersolid phenomena through blocking experiments.

Contribution

It provides new insights into the geometric dependence of NCRI and extends previous experiments to show the nonlocal characteristics of supersolidity in solid helium-4.

Findings

Maximum NCRI of 20% at 100 micrometer annuli

Suppression of NCRI below 1% in porous or larger geometries

Blocking the annulus reduces NCRI, indicating nonlocal effects

Abstract

We study the effect of confinement on solid 4-He's nonclassical rotational inertia (NCRI) in a torsional oscillator by constraining it to narrow annular cells of various widths. The NCRI exhibits a broad maximum value of 20% for annuli of approximately 100 micrometer width. Samples constrained to porous media or to larger geometries both have smaller NCRI, mostly below about 1%. In addition, we extend Kim and Chan's blocked annulus experiment to solid samples with large supersolid fractions. Blocking the annulus suppresses the nonclassical decoupling from 17.1% below the limit of our detection of 0.8%. This result demonstrates the nonlocal nature of the supersolid phenomena. At 20 mK, NCRI depends on velocity history showing a closed hysteresis loop in different thin annular cells.