- Published on 14 September 2010
New experiments on the flow of solid He through a microscopic hole reveal a mechanism that triggers the geysers based on the breakdown of a plug located upstream of the source chamber.
The vacuum expansion of solid helium through a micrometric orifice was suggested as a mean to inject excess vacancies into the solid bulk [R. Grisenti et al, J. Electr. Spectr. 129 (2003) 201]. But while the He flow seems smooth, unexpected periodic bursts out of the orifice (geyser effect) are observed during these vacuum expansion experiments.
The results presented in this Highlight paper indicate that the geyser collapse does not occur near the orifice, as previously suggested, but at a plug in the feed line upstream of the source chamber. Each collapse is triggered by the increasing vacancy concentration which makes the solid behave much as a liquid.
On this basis, Benedek, Nieto and Toennies argue that vacuum expansion provides a novel approach for investigating exotic non-equilibrium phases of quantum solids such as helium.