Experimental studies in solid state and low temperature physics. Progress report for 1976

Experimental investigations are being carried out in a broad area of low-temperature and solid-state physics which includes superconductivity, magnetism in metals and liquid and solid helium. The pair-field susceptibility of superconductors is being studied. A propagating mode in the phase of the superconducting order parameter is under investigation. Superconducting fluctuations are being used to probe critical fluctuations in magnetic systems using the proximity effect. Heat capacities of super-conducting films in the vicinity of T/sub c/ are also being investigated. The properties of thin film solid solutions of sodium in ammonia are being studied. Nuclear orientation studies of the dilute magnetic impurity problem in metals in the 1 mK temperature region are being carried out. Refrigeration requirements for this work are being met using enhanced hyperfine nuclear cooling. The quantization of circulation in superfluid liquid 4He is being investigated using the Vinen method. The dynamics of superfluid flow through submicron pores are being studied in both pure 4He and in 3He/4He mixtures in an apparatus provided with a 3He refrigerator. The same apparatus is being used to study second sound in 3He/4He mixtures. Measurements of the differential osmotic pressure of 3He/4He liquid mixtures near the tricritical point have shown a peak in the ''concentration susceptibility'' at the lambda line. Data obey a simple tricritical scaling relation with some discrepancy visible for T > T/sub lambda/