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Current work supported by DMR-1101189

Research


Overview

Research in Gasparinilab focuses on coupling and proximity effects in superfluid 4He. We confine 4He in two regions that are in contact with each other. The standard proximity effect theories say that the thermodynamic responses of each region should only be affected within a short distance of the interface, roughly the correlation length. Recently however we have measured several responses that are affected at distances several times this length, and thus are not explained within the conventional proximity effect theories. The aptly coined "Giant Proximity Effects" we measure have also been measured in the high temperature superconducting cuprate systems which we believe share the same underlying physics.

Confinements

Our confinements are achieved between two bonded silicon oxide wafers. An oxide layer is grown on 2 inch silicon wafers and then patterned to produce the desired confining structures using photolithography. The two wafers are then bonded to one another and filled with helium via a hole drilled through the top wafer.

Coupled Specific Heat

One of our recent measurements showed that a (2 μm)3 confinements of 4He can be strongly coupled to neighboring confinements under certain conditions. We measured a ~9% enhancement in the specific heat of these confinements when they are spaced 2 μm edge-to-edge compared to when they are spaced 4 μm edge-to-edge and effectively isolated from each other. We have also measured an increase in the magnitude of the specific heat of a uniform 4He film when in contact with these larger (2 μm)3 confinements.

Proximity Enhanced Superfluid

We have also measured an enhancement in both the magnitude and transition temperature of the amount of superfluid in a 4He film. This enhancement varies systematically with the spacing of larger confinements in contact with the film.
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Last Updated: Wednesday, 24-Aug-2011 15:38:54 EDT by JKP