project title: Search for new features in the melting pressure of 4He and new facets of solid 4He
project leader: Prof. R. Jochemsen, Mr. Juan Bueno, and Mr. Duyha Nguyen
access given (in days): 90
access used (in days): 91
local host: Harry Alles
home institution: Leiden University, Kammeligh Onnes Laboratory
country of institution: The Netherlands
starting date (yyyy-mm-dd): 2006-04-11
The first task of this project is to investigate whether on the melting curve of 4He any anomaly could be seen near 0.2K. Below that temperature recently a nonclassical rotational inertia of solid 4He has been observed by US scientists Eun-Seong Kim and Moses Chan who have interpreted their results as an evidence of supersolid behavior. We aim to measure the melting pressure of solid 4He with the accuracy of better than 1 microbar from about 0.4K down to the lowest temperature of a few mK. In these experiments we will also follow the crystal shape during temperature sweeps. Another task of that project is to search for new facets (smooth crystal faces) on the surface of 4He crystals. According to theory, the lower the temperature, the more different types of facets should be seen on the crystal surface. In 4He, however, only three different types have been observed so far.
As an outcome of this project, the melting curve of 4He was measured in the temperature range from 10 to 400 mK with the accuracy of about 0.5 microbar and no sign of a supersolid transition was detected near 0.2 K. Below 80 mK, a small deviation from the expected T to the fourth dependence due to phonons was found which in our later measurements turned out to be caused by the temperature dependence of our pressure gauge sensitivity. Our results were published in Physical Review Letters 97, 165302 (2006): I.A. Todoshchenko, H. Alles, J. Bueno, H.J. Junes, A.Ya. Parshin, and V. Tsepelin, "Melting Curve of 4He: No Sign of a Superolid Transition down to 10 mK" This project was completed during the 3rd reporting period of ULTI trans-national access program. During the 4th reporting period the users (the research team of Dr. Reyer Jochemsen form Leiden University) attended the ULTI users meeting, held in Espoo, Finland in 28.-30. 2008, and gave a report on the final analysis of the results.