Performance of adiabatic melting as a method to pursue the lowest possible temperature in ${}^3$He and ${}^3$He-${}^4$He mixture at the ${}^4$He crystallization pressure

Abstract

We studied a novel cooling method, in which ${}^3$He and ${}^4$He are mixed at the ${}^4$He crystallization pressure at temperatures below $0.5\mathrm{mK}$. We describe the experimental setup in detail, and present an analysis of its performance under varying isotope contents, temperatures, and operational modes. Further, we developed a computational model of the system, which was required to determine the lowest temperatures obtained, since our mechanical oscillator thermometers already became insensitive at the low end of the temperature range, extending down to $\left(90\pm 20\right)\mu \mathrm{K}\approx \frac{T_c}{\left(29\pm 5\right)}$ ($T_c$ of pure ${}^3$He). We did not observe any indication of superfluidity of the ${}^3$He component in the isotope mixture. The performance of the setup was limited by the background heat leak of the order of $30\mathrm{pW}$ at low melting rates, and by the heat leak caused by the flow of ${}^4$He in the superleak line at high melting rates up to $500\mu mol/s$. The optimal mixing rate between ${}^3$He and ${}^4$He, with the heat leak taken into account, was found to be about $\mathrm{100..150}\mu mol/s$. We suggest improvements to the experimental design to reduce the ultimate achievable temperature further.

arXiv comment39 pages, 24 figures

References in corpus (14)

• A Mixture of Bose and Fermi Superfluids
• Quartz Tuning Fork: Thermometer, Pressure- and Viscometer for Helium Liquids
• Two-Element Mixture of Bose and Fermi Superfluids
• Cooling and thermometry of atomic Fermi gases
• Critical Velocity and Dissipation of an ultracold Bose-Fermi Counterflow
• Self-localization of magnon Bose-Einstein condensates in the ground state and on excited levels: from harmonic to box-like trapping potential
• Induced interactions in a superfluid Bose-Fermi mixture
• Dry demagnetization cryostat for sub-millikelvin helium experiments: refrigeration and thermometry
• Thermodynamically consistent equilibrium properties of normal-liquid Helium-3
• Relaxation of Bose-Einstein Condensates of Magnons in Magneto-Textural Traps in Superfluid ${}^3$He-B
• Effects of ${}^4$He film on quartz tuning forks in ${}^3$He at ultra-low temperatures
• Measurements on Melting Pressure, Metastable Solid Phases, and Molar Volume of Univariant Saturated Helium Mixture
• Corrections to the Higgs Mode Masses in Superfluid 3He
• Thermodynamics of adiabatic melting of solid ${}^4\mathrm{He}$ in liquid ${}^3\mathrm{He}$

Cited by in corpus (1)

• Properties of fermionic systems with the Path-integral ground state method