Review paper: Heat transfer between liquid helium and solids below 100 mK

Abstract

The many experimental determinations of heat transfer between liquid helium and solids are reviewed and compared with the existing theories. Generally heat transfer is a complex process at low temperatures, involving parallel heat paths with several resistances in series in each path. The standard theories for the individual resistances are reviewed and as far as possible a definite value of the expected resistance obtained. ddute He m hqutd He, metals m liquid He, metals m dtlute He m hquld 4He, and miscellaneous experiments. Where appropriate, the experimental results have been reevaluated in terms of standard models for heat transfer and presented as resistance versus temperature on diagrams showing the theoretical predictions. Between 20 and lOOmK many measurements show good agreement with acoustic mismatch theory for thermal boundary resistance. Below 20 mK most experiments have been made with finely divided solids (sintered metals or powdered paramagnetic salts); invariably the resistance has been anomalously low, with the metal/3He systems showing RocT -1 and the metal/dilute 3He in * . -3 9He systems showing RocT . The cerium magnesium nitrate/helium experiments have shown a temperatureindependent resistance and sometimes an RecT -~ dependence. These resistances have been attributed to the spin-lattice resistance in cerium magnesium nitrate. Evidence[or heat transfer by magnetic coupling has been reviewed and it is concluded that the positive evidence has other explanations, while the lack of dependence upon helium pressure, 3He phase, and large magnetic fields is strong negative evidence. If the disagreement of experimental results with standard theory is not to be attributed to magnetic coupling, then several theoretical questions remain to be answered; these questions are posed. Basically, at low temperatures the excitations in solids and liquid helium have wavelengths and mean free paths much larger than the size of the finely divided particles or pores between the particles. Thus theories for bulk solids and bulk liquid helium are not appropriate for describing excitations and their interactions at these low temperatures. 467 0022-2291/79/1200-0467503.00/0 ~) 1979 Plenum Publishing Corporation 468 J.P. Harrison

Progress in Cooling Nanoelectronic Devices to Ultra-Low Temperatures

“…Cooling by demagnetisation often uses elaborate refrigeration stages [74] on state-of-the-art, custom-built dilution refrigerators [73], or vibration isolated systems on commercial, cryogen-free dilution refrigerators [78,79]. While these systems can readily reach bulk electron temperatures ∼ 100 μK , it is not straightforward to use them to cool a nanoelectronic sample to similar temperatures.…”

“…10a and b. This cryostat also has the inherent benefit of lower mechanical vibrations because there is no pulse-tube cooler, from which [107] there can be a significant additional heat leak through eddy-current heating [79,88] and additional electrical noise [108]. The particular dilution refrigerator used for the results shown in Fig.…”

Giant thermomechanical effect in normal liquid 3He

“…The probability for energy exchange by a 3 He quasiparticle can be deduced from the Kapitza thermal boundary resistance [38,39]. In his review Harrison concluded that a lower limit had been reached at RT ∼ 300 K 2 /W for 1 cm 3 of sintered metal powder heat exchanger.…”

Tunneling Systems in Amorphous and Crystalline Solids

“…This idea has been realized in Hunklinger et al (1973), Graebner and , Harrison (1979), Hu and Walker (1977), Hunklinger et al (1973), and Hunklinger and Arnold (1976), for example, in various modifications of the dipole echo experimental technique. Consequently many experimental methods that are useful for studying magnetic systems remain relevant for the analysis of TS's in amorphous solids.…”