The Thermal Conductivity of Solid 4he in Vycor

Open Access
Author:
Omelchenko, Stefan Thomas
Area of Honors:
Interdisciplinary in Engineering Science and Physics
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Moses Hung Wai Chan, Thesis Supervisor
  • Michael T Lanagan, Honors Advisor
  • Judith A Todd, Faculty Reader
  • Richard Wallace Robinett, Honors Advisor
Keywords:
  • helium
  • Vycor
  • supersolid
  • superfluid
Abstract:
Liquid 4He becomes a superfluid and flows with zero viscosity below 2.176 K. In 2004, a similar phenomenon was observed in solid 4He, when a fraction of the solid apparently decoupled from the motion of the crystal lattice. Kim and Chan first observed this phenomenon, known as non-classical rotational inertia (NCRI), in torsional oscillator experiments. The detection of NCRI points to a superfluid phase in solid 4He, which since has been termed supersolid. Further work by Lin et al. showed a broad peak in the specific heat of solid 4He on top of the Debye T3 term near the onset of NCRI. This is indicative of a thermodynamic phase transition. Still, more experimental work is needed to verify that this is a supersolid phase. A characteristic phenomenon of the superfluid transition is the divergence of the thermal conductivity of liquid 4He near 2.17 K. It is interesting to consider whether a similar anomaly appears in the thermal conductivity of solid 4He appears near the supposed supersolid transition. Previous measurements of the thermal conductivity of bulk solid 4He did not observe any anomalous behavior near the supersolid onset. However, NCRI has been reported in both bulk solid 4He samples and solid 4He in porous media. These facts motivated us to measure the thermal conductivity of solid 4He in Vycor, a porous glass. In order to do so we were required to construct a leak-tight Vycor cell capable of withstanding the immense pressures and high stresses of extremely low temperatures. We overcame these obstacles by constructing a cell comprised of a cylindrical Vycor rod coated with Stycast 2850 and held by copper supports. Counter intuitively, the thermal conductivities of the empty Vycor cell and the solid 4He were not additive. This fact prompted us to examine the ratio of the thermal conductivity of the 4He-Vycor system to that of the empty cell. A small “dip” was observed in this plot near the onset of the supersolid transition.