![]() Since dislocation motion depends on crystal structure it was important that these measurements be extended to the hexagonal close packed phase of (3)He, not just the body centered cubic phase. ![]() In order to clarify the relationship between the shear modulus and torsional oscillator behaviors, we have recently made modulus measurements on (3)He, where no supersolid response is expected. A question then arises: are the modulus increases responsible for the frequency changes seen in torsional oscillator experiments? The expected frequency shifts appear to be much too small to explain the apparent decoupling, nor can elastic effects explain the 'blocked annulus' results or the behavior in small pores. We attribute the shear modulus effects to the elastic response of mobile dislocations and their pinning by (3)He impurities at low temperatures. In these and other ways, the shear modulus closely mirrors the torsional oscillator behavior and it is clear that the two phenomena are closely related. The modulus anomaly is frequency independent, depends strongly on strain amplitude, and is very sensitive to (3)He impurities. In hexagonal close packed (4)He, the shear modulus increases dramatically below 200 mK, the temperature range where decoupling is seen in torsional oscillators. We have developed a new technique for measuring the shear modulus of solid helium at low frequencies and small strains. A brief discussion is given of the use of this technique in the discovery of superfluid helium 3 by Osheroff, Richardson and the author at Cornell.Following recent torsional oscillator measurements which appear to show the 'non-classical rotational inertia' which characterizes a supersolid, a number of experiments have searched for evidence of unusual behavior in other properties. While this author was a graduate student at Yale, Henry Fairbank pointed out to him the possibility of cooling helium three via adiabatic compression from the liquid into the solid phase. ![]() It was found via ultrasound experiments that a small silver of bcc solid existed at the lowest pressures. Hitherto it had been thought that hcp was the stable phase throughout the low temperature part of the phase diagram. In studies of solid helium four at Yale, a surprising observation was made. Much of the later work in this area was performed by the group of John Wheatley at the University of Illinois. The main emphasis in this work was to search for Fermi liquid behavior. Early evidence for the melting curve minimum was found. As more helium three became available, studies of pure helium three were performed, including measurements of the thermal conductivity, the density and the specific heat. The calculations showed the possibility of transferring helium atoms to superstable states with the release of a huge amount of energy, provided that helium was previously converted to a solid state at a sufficiently high pressure and low temperature. These measurements showed strong effects of the phase separation in helium 3 - helium 4 mixtures previously discovered in the laboratory of William Fairbank (a student of Lane and a brother of Henry Fairbank). Abstract The results of quantum-chemical calculations of helium atoms in strong and superstrong magnetic fields are described. Henry Fairbank’s graduate students were provided with the opportunity to investigate second sound in dilute and later concentrated mixtures of helium three in superfluid helium four. Following World War II small amounts of helium three became available to low temperature experimenters. ![]() This discussion will mainly treat the contributions of Henry Fairbank and his students during the period between 19, when Henry Fairbank left Yale to become chairman of the Physics Dept. Lane who came to Yale in 1932 and Henry A. Many of the foundations of low temperature physics in the latter half of the twentieth century were built at Yale University under the leadership of Professor Cecil T. ![]()
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