QFS 2016 Book of Abstracts

Abstracts

P4.4 Added mass of He II in experiments with oscillating quarts tuning fork I. Gritsenko, K. Klokol, S. Sokolov, and G. Sheshyn ILTPE - B.Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine Using the method of quartz tuning fork the temperature and pressure dependences of resonance frequency of the tuning fork, for T = 0.1 – 1.5 K and P = 1 – 24.8 atm, were measured and the amount of He II entrained by vibrating prong of the fork (added mass) was determined in the laminar flow regime. Quartz tuning forks with different resonance frequencies 6.65 kHz, 8.46 kHz, 12.1 kHz, 25.0 kHz, 33.6 kHz were studied. It was found that at T 1 K added mass per unit length of the fork prong and added mass coefficient depends on frequency. In addition we checked that, at T = 365 mK, the added mass changes with pressure according to the density change of He II with pressure. P4.5 Strong Coupling Effects and Shear Viscosity in an Ultracold Fermi Gas Daichi Kagamihara, Yoji Ohashi Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan We theoretically investigate the shear viscosity η , as well as the entropy density s, in the normal state of an ultracold Fermi gas. Including pairing fluctuations within the framework of a T-matrix approximation, we calculate these quantities in the BCS-BEC crossover region. We evaluate the ratio η /s, to assess the lower bound of this ratio, conjectured by Kovtun, Son, Starinets (KSS). In the crossover region, this ratio is found to decrease with increasing the interaction strength, to become very close to the KSS bound slightly in the BEC side at the superfluid phase transition temperature.

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