The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Experiments on the Faceting and Supersolidity in Helium Crystals

Heikki Junes

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium AS1 at Helsinki University of Technology (Espoo, Finland) on Friday 20th of February, 2009, at 12 noon.

Overview in PDF format (ISBN 978-951-22-9745-0)   [6195 KB]
Dissertation is also available in print (ISBN 978-951-22-9744-3)

Abstract

This Thesis describes investigations on the solid-liquid interface of helium. Helium crystals represent a unique model system for the studies of the crystalline phenomena, such as faceting and crystal growth, and their surface can be studied, in principle, down to the zero temperature quantum limit (0 K = −273.15°C). Helium also becomes extremely pure at low temperatures as all the impurities except the isotopical ones freeze out. In this Thesis the solid-liquid interfaces of both helium-3 and helium-4 have been studied using a Fabry-Pérot interferometer and a high-accuracy pressure gauge.

The optical studies on the faceting of helium-3 crystals have revealed that the quantum motion of the interface, which keeps the solid-liquid interface rough (not faceted) down to 0.1 K, becomes damped at low temperatures. The quantum fluctuations of the interface become more and more damped due to the Fermi-degeneracy of the liquid which creates a bottle-neck for the spin transport through the moving interface. As a result, facets start to appear and, finally, at the lowest temperatures below 0.001 K the solid-liquid interface becomes so localized that it resembles the surface of classical crystals.

The melting curve of high-quality helium-4 crystals has been measured between 0.01–0.32 K with an accuracy of 0.1 Pa without finding any entropy signature which the possible supersolid transition could cause. The entropy below 0.3 K was attributed to phonons in solid and in liquid and the upper limit of the non-phonon entropy was set to 5 · 10−8 R. The measurements on the thermal expansion of liquid helium-4 between 0.02–0.72 K in constant volume pointed out that the rotons start to contribute to the thermodynamics of the solid-liquid interface of helium-4 above 0.3 K. In order to study the role of defects in the possible supersolidity, also the stacking faults were studied on helium-4 crystals.

This thesis consists of an overview and of the following 10 publications:

  1. Igor A. Todoshchenko, Harry Alles, Heikki J. Junes, Alexander Ya. Parshin, and Viktor Tsepelin. 2005. Measurements on the surface tension of 3He crystals near 100 mK. Journal of Low Temperature Physics, volume 138, numbers 3-4, pages 811-816.
  2. Igor A. Todoshchenko, Harry Alles, Heikki J. Junes, Alexander Ya. Parshin, and Viktor Tsepelin. 2003. Faceting of 3He crystals. Physica B, volumes 329-333, pages 386-387. © 2003 Elsevier Science. By permission.
  3. I. A. Todoshchenko, H. Alles, H. J. Junes, A. Ya. Parshin, and V. Tsepelin. 2004. Surface of a 3He crystal: Crossover from quantum to classical behavior. Physical Review Letters, volume 93, number 17, 175301. © 2004 American Physical Society. By permission.
  4. Igor A. Todoshchenko, Harry Alles, Heikki J. Junes, Alexander Y. Parshin, and Viktor Tsepelin. 2007. Growth dynamics and faceting of 3He crystals. Journal of Low Temperature Physics, volume 148, numbers 5-6, pages 635-643.
  5. H. J. Junes, H. Alles, A. Ya. Parshin, I. A. Todoshchenko, and V. Tsepelin. 2007. First observation of the critical size of facets on 3He crystals near 1 mK. Journal of Low Temperature Physics, volume 146, numbers 1-2, pages 85-93.
  6. I. A. Todoshchenko, H. Alles, H. J. Junes, and A. Ya. Parshin. 2006. On the growth dynamics of 4He crystals near the first roughening transition. In: Y. Takano, S. P. Hershfield, S. O. Hill, P. J. Hirschfeld, and A. M. Goldman (editors). Proceedings of the 24th International Conference on Low Temperature Physics. Orlando, Florida, USA. 10-17 August 2005. AIP Conference Proceedings, volume 850, pages 337-338.
  7. I. A. Todoshchenko, H. Alles, J. Bueno, H. J. Junes, A. Ya. Parshin, and V. Tsepelin. 2006. Melting curve of 4He: No sign of a supersolid transition down to 10 mK. Physical Review Letters, volume 97, number 16, 165302. © 2006 American Physical Society. By permission.
  8. I. A. Todoshchenko, H. Alles, H. J. Junes, A. Ya. Parshin, and V. Tsepelin. 2007. Absence of low temperature anomaly on the melting curve of 4He. Pis'ma v ZhETF, volume 85, number 9, pages 555-558. Reprinted in Journal of Experimental and Theoretical Physics Letters, volume 85, number 9, pages 454-457. © 2007 MAIK Nauka/Interperiodica. By permission.
  9. I. A. Todoshchenko, H. Alles, H. J. Junes, M. S. Manninen, A. Y. Parshin, and V. Tsepelin. 2008. Elementary excitations in solid and liquid 4He at the melting pressure. Journal of Low Temperature Physics, volume 150, numbers 3-4, pages 258-266.
  10. H. J. Junes, H. Alles, M. S. Manninen, A. Y. Parshin, and I. A. Todoshchenko. 2008. Stacking fault energy in 4He crystals. Journal of Low Temperature Physics, volume 153, numbers 5-6, pages 244-249.

Errata of publications 5 and 9

Keywords: quantum crystals, helium-3, helium-4, crystal growth, supersolidity, melting curve, stacking fault

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© 2009 Helsinki University of Technology

Last update 2011-05-26