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the first time the full solubility curve of 3He in 4He up to the crystallization pressure. Earlier measurements have not been extended above 22 bar due to the ordinary capillaries becoming blocked by solid He at some higher temperature, whereas our cell, equipped with the superfilter filling lines, could be loaded all the way up to the crystallization pressure at any temperature. Precise data was obtained by using the quartz oscillator as the sensing element, which is a new technique for this purpose. Another quantity investigated was the osmotic pressure of 3He in the mixture at the crystallization pressure as the function of 3He concentration. Unprecedentedly accurate data was obtained by using our ultra-sensitive pressure gauge, actually forming the experimental volume for this run. Both the solubility data as the function of pressure and the osmotic pressure data as the function of concentration, and their temperature dependences, of course, can be used to deduce the mutual interactions between the 3He quasiparticles in the liquid solution. This, in turn, is the essential starting point in order to make predictions upon the eventual superfluid transition temperature and of the pairing state of the dilute fermion system of 3He in 4He. Such analysis on the basis of our new data is under way.

Some other intriguing observations during these measurements, which have not yet been systematically treated, however, include (i) the observation of very strong second sound resonances exited and sensed by the quartz forks below and above one kelvin in the mixtures, (ii) quantum nucleation events of the pure 3He phase from the homogeneous mixture prepared into the state of supersaturation, and (iii) the possibility to operate the quartz resonators free from any attenuation at low temperatures both in vacuum and in pure superfluid 4He.

Towards the end of the year, the preparations to move to the new laboratory facilities forced to pause the experiments at the big cryostat. Before the turn of the year the installation was taken apart and its reconstruction at the new building was started.

ROTA group

V.B. Eltsov, R. de Graaf, P. Heikkinen, J. Hosio, R. Hänninen, M. Krusius, and R.E. Solntsev

Visitors: Yu.M. Bunkov, A. Golov, R.P. Haley, V. Lebedev, V. L’vov, W. Schoepe, E. Sonin, M. Tsubota, D.E. Zmeev, and H. Yano

DYNAMICS AND TURBULENCE IN COHERENT QUANTUM SYSTEMS

The low-temperature many-body particle systems with macroscopic quantum behaviour are generally associated with superfluidity, owing to the requirement of coherent particle motion. The hallmark is a persistent supercurrent, which flows unattenuated for ever. However, at higher flow velocity quantized vortex lines are formed and their motion becomes dissipative, even turbulent in the limit of low dissipation at low temperatures. The turbulence persists on approaching the zero temperature limit and, if the external drive is switched off, it decays. This situation, the existence of finite dissipation at absolute zero temperature, has been proven in a few different measurements during the past years. Such results demonstrate that there exist new mechanisms by which the motion of superfluid vortices becomes lossy even at the very lowest temperatures.

The second important property about the zero temperature limit is the coupling from the external reference frame to the superfluid fraction. This coupling vanishes exponentially as T One might therefore think that a finite dissipation level is

Annual Report 2007

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