X hits on this document

188 views

0 shares

0 downloads

0 comments

29 / 84

–  29  –

increased by adjusting their orientation close to horizontal. We have succeeded to create several such crystals. We have also succeeded to detect small higher order facets from interferograms where we have plotted histograms of the orientations of the crystal surface. As a result of our careful analysis, we have discovered the fourth and fifth facets on the surface of hcp 4He crystals in [10-12] and [11-20] directions, respectively.

MEASUREMENTS ON THE STEP ENERGIES OF 4He CRYSTALS

Harry Alles, Heikki Junes, Matti Manninen, and Igor Todoshchenko

Collaborator: Alexander Parshin

Before our experiments only the step energy of the basal [0001] facet was known in 4He. We have succeeded in measuring the step energy of the second [10-10] facet and found it to be close to the value of the step energy of the basal facet.  This was done with a novel method which we have developed in our studies of 3He crystals. In this method the crystal is subjected to a very slow melting and the facet size is monitored until it reaches the critical size and collapses. The value of the critical size of the facet, together with the value of the overpressure on the facet, yields the step free energy of the facet. Measurements on the third, [10-11] facet show that its step energy is too small to be measured with this method. To measure the step energy of the [10-11] facet we have adopted another method which is based on the measurement of the growth threshold of the facet. In this method the crystal is grown slowly. The facet remains initially immobile until the overpressure exceeds a certain threshold value which depends on the step energy and the density of dislocations. The dislocation density can be found by measurements of the threshold for the facets with known step energy. We hope to complete the analysis of our data on 4He crystals by the end of 2008.

CONSTRUCTING NEW EXPERIMENTAL CELL FOR THE SEARCH OF CRYSTALLIZATION WAVES IN 3He

Harry Alles, Heikki Junes, Matti Manninen, and Igor Todoshchenko

Collaborators: Alexander Parshin and Viktor Tsepelin

We have recently started to design and build a new experimental cell for the studies of liquid-solid interface of 3He at ultra low temperatures. The ultimate goal of the following experiments is to observe magnetic crystallization waves which are predicted to exist in 3He at a temperature of a few tenths of mK. The new cell will be placed into the YKI cryostat in 2009.

THEORY group

LTL has a long tradition of successful collaboration between theorists and experimental groups. The in-house theoreticians are also attacking substantial problems posed by experiments or theory made elsewhere, if these fall within their expertise.

Our experimental program in ultra low temperature quantum phenomena (ROTA team) has traditionally had the strongest theory support, which today is provided by Grigory Volovik, Nikolai Kopnin (50%) and Risto Hänninen. The INTERFACE group relies in its theory support mostly on the short term visits of Alexander Parshin

Annual Report 2007

Document info
Document views188
Page views188
Page last viewedMon Dec 05 15:12:33 UTC 2016
Pages84
Paragraphs1563
Words29595

Comments