Avalanches in the draining of nanoporous Nuclepore mediated by the superfluid helium film

Abstract

When capillary-condensed superfluid ${}^{4}\mathrm{He}$ drains from pore spaces in the nanoporous material Nuclepore, the fluid drains in a series of large-scale avalanches in which substantial numbers of pores (up to $\ensuremath{\sim}2.5%$ of the sample) drain as a single cooperative event. In this work we document the behavior of such avalanches in a number of different multiple-detector configurations in an effort to investigate the origin of the interactions among the pores that lead to the avalanche behavior. We conclude that the presence of a superfluid ${}^{4}\mathrm{He}$ film on the surface of the Nuclepore plays a significant role in causing the avalanche behavior. We also investigate aspects of the spatial distribution of pores that are involved in an avalanche event, and conclude that avalanche events involve pores that are distributed over the entire sample; avalanches do not typically involve a high-density cluster of pores in a local region of the substrate.