Heat Transport by Liquid Helium through Aerogel

James A. Sauls, Northwestern University, DMR 0805277

Silica Aerogel is very low density glass (SiO2) formed by a sol-gel process. The material is a solid, but with 1/100 the density of typical glass. Aerogels are optically transparent (see image) indicative of their rarefied atomic structure. Many physical properties derive from the random, yet correlated, arrangement of the SiO2 clusters. A computer generated model of the atomic arrangement of the SiO2 structure, based on the theory of diffusion limited cluster aggregation (DLCA), shows the open structure on the scale of 500 nm (expanded image).1

Transport of heat, sound and light through liquid Helium (3He) provides an ideal medium in which to study the structure of silica aerogel. We have obtained exact solutions to the Boltzmann equation for heat transport through liquid 3He that fills the open space of the aerogel structure.1 This result provides a method for quantitative analysis of transport experiments, and a means of testing theoretical models for the role of correlations in the spatial arrangement of SiO2 clusters on the transport of mass, energy and magnetization in these remarkable solids.

1. S. Ali, P. Sharma and J. A. Sauls, to be published (2009).

Upper left: 98.5% porous aerogel (Northwestern), center: DLCA model (S. Ali, Northwestern), right: 2D slice. The scale of the image is 500 nm on an edge.

Suppression of heat transport for 3He in aerogel: (black) exact solution, (red) scaling function [accurate to better than 1% over the temperature range, 1-100 mK, and pressure range, 0-34 bar], and (blue) heat conductivity for pure 3He.

✓ The PI delivered the Erasmus Mundus Lecture on Nanotechnology in Modern Society: Superconductivity and Magnetism down to the Nanoscale in February 2009 at Chalmers University, Gothenburg Sweden. The lecture was videocast to students at universities in Delft, Leiden, Leuven and Dresden [Lecture].

VORTEX STRUCTURE & DYNAMICSAUGUST 11-12, 2009SATELLITE WORKSHOP OF QFS2009

VORTEX STRUCTURE & DYNAMICSAUGUST 11-12, 2009SATELLITE WORKSHOP OF QFS2009

QFS2009: International Symposium on Quantum Fluids and Solids

August 5-11, 2009 - Northwestern University, Evanston, Illinois, USA

QFS2009: International Symposium on Quantum Fluids and Solids

August 5-11, 2009 - Northwestern University, Evanston, Illinois, USA

Magneto-acoustic and Quantum Transport in Helium

James A. Sauls, Northwestern University, DMR 0805277

✓ Northwestern University was host to the International Symposium on Quantum Fluids and Solids, QFS2009 [website]. The PI chaired the program committee for 50 invited speakers, 200 poster presentations and 245 participants. The conference brought together distinguished scientists and young researchers from Brazil, Canada, Europe, Israel, Japan, Korea, Russia, Ukraine and the USA.

✓ The PI organized a workshop on Vortex Structure and Dynamics with approximately 40 participants, as a satellite meeting following QFS2009. The focus was on topics ranging from the structure of topological defects in superfluid 3He, vortex dynamics and dissipation in

superconductors to the possible role of vortices in the anomalous dynamics of solid 4He.