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Supersolid transiion of ?He

by 1971- Kim, Eunseong

Abstract (Summary)
iii The first experimental observation of supersolid 4He is presented for both bulk solid helium and solid 4He confined in porous media. Non-Classical Rotational Inertia (NCRI), direct evidence of the existence of a supersolid, is detected by the reduction in the resonant period of the torsional oscillator. For bulk solid 4He torsional oscillator measurements have been performed in the temperature range of 0.02K to 2K, for pressures between 26 bars and 66 bars. Below 0.23K, non-classical rotational inertia is detected by a sharp drop in the resonant period of the torsional oscillator, indicating entry into a supersolid phase. The temperature dependence of the supersolid fraction exhibits a universal behavior of an exponential-like rise with decreasing temperature and then a saturation in the low temperature limit. This temperature dependence is distinct from BEC in other systems such as superfluid liquid helium and dilute atomic gases. For all pressures a very strong dependence of nonclassical rotational inertia on the oscillation speed is observed. The scatter in the supersolid fraction, varying between 0.7% and 1%, makes it difficult to conclude if there is any trend of the supersolid fraction with increasing pressure. Solid 4He confined in porous Vycor glass has been studied between 0.03K and 2K, for pressures ranging from 40 to 65 bars. NCRI is detected below 0.175K for all samples that we have studied. The fractional NCRI at low temperature ranges from 0.2% to 0.5%. The presence of disordered porous media does not alter the supersolid transition. The fractional NCRI of solid 4He confined in Vycor glass resembles that of bulk solid 4He, iii exhibiting strong oscillation speed dependence as well as universal temperature iv dependence. For solid mixtures with very dilute concentration of 3He reveals a very intriguing behavior. The addition of 3He not only broadens the transition but also enhances the transition temperature as opposed to the effect of 3He in the superfluid helium. iv
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School:Pennsylvania State University

School Location:USA - Pennsylvania

Source Type:Master's Thesis

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