Using fourth-sound techniques, we have measured the depression of the superfluid fraction of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ confined in small pores of packed powder over wide temperature ($0.2<\mathrm{}\frac{T}{T_c}<1\mathrm{}$) and pressure ($0.5<p<\mathrm{}20\mathrm{}$ bars) ranges. From the analysis of the data we determine the magnitude and the pressure dependence of the healing length. The healing length decreases from 520 Å at 0.5 bar to 200 Å at 20 bars. The values are in fair agreement with those expected from the BCS expression.

• Received 29 December 1986

DOI:https://doi.org/10.1103/PhysRevLett.58.1949