Supersolid Transition of 4He

Author:

Kim, Eunseong

Graduate Program:

Physics

Degree:

Doctor of Philosophy

Document Type:

Dissertation

Date of Defense:

June 09, 2004

Committee Members:

Moses Hung Wai Chan, Committee Chair/Co-Chair
Jayanth R Banavar, Committee Member
Milton Walter Cole, Committee Member
James Bernhard Anderson, Committee Member
Julian Decatur Maynard Jr., Committee Member

Keywords:

Bose Einstein Condensation
Superfluidity
Quantum solid
Phase Rransition

Abstract:

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), a 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 range of temperature from 2K to 0.02K and pressure from 26 bars to 66 bars. Below 0.27K, 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 other BEC systems such as superfluid of liquid helium and Bose-Einstein condensation of dilute gases. For all pressures very strong dependence of non-classical rotational inertia on the oscillation speeds is observed. The scatters 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 in the range of temperature from 2K to 0.03K and pressure 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, exhibiting strong oscillation speeds dependence as well as universal temperature 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 transition temperature as opposed to the effect of 3He in the superfluid helium.