FERMI PAIRING IN DILUTE <sup>3</sup>He-HeII MIXTURES

Al-Sugheir, M. K.; Ghassib, H. B.; Joudeh, B. R.

doi:10.1142/s0217979206034844

Cited by 16 publications

(89 citation statements)

References 13 publications

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“…Strong motivation for pursuing ever lower temperatures in helium fluids is the anticipated superfluid transition of the 3 He component in dilute 3 He- 4 He mixtures. Pure liquid 3 He undergoes superfluid transition when fermionic 3 He atoms 1 3 Journal of Low Temperature Physics (2020) 199:1230-1267 start to form BCS-like pairs [1].…”

Section: Introductionmentioning

confidence: 99%

Performance of Adiabatic Melting as a Method to Pursue the Lowest Possible Temperature in $$^{3}\hbox {He}$$ and $$^{3}\hbox {He}$$–$$^{4}\hbox {He}$$ Mixture at the $$^{4}\hbox {He}$$ Crystallization Pressure

2020

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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 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 (90 ± 20) μK ≈ T c (29±5) (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 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 μmol/s. The optimal mixing rate between 3 He and 4 He , with the heat leak taken into account, was found to be about 100..150 μmol/s. We suggest improvements to the experimental design to reduce the ultimate achievable temperature further.

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Section: Introductionmentioning

confidence: 99%

Performance of Adiabatic Melting as a Method to Pursue the Lowest Possible Temperature in $$^{3}\hbox {He}$$ and $$^{3}\hbox {He}$$–$$^{4}\hbox {He}$$ Mixture at the $$^{4}\hbox {He}$$ Crystallization Pressure

2020

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“…In the quest for superfluidity of 3 He in 3 He− 4 He mixture, we are in a similar situation: We have exhausted the search space available using the present cooling techniques, and hence a new approach is needed. The target temperatures are below 100 μK, where a BCS-type superfluid transition is expected to occur between weakly interacting 3 He atoms in the isotope mixture [5][6][7][8]. Such a system would be a unique dense doublesuperfluid ensemble consisting of fermionic 3 He and bosonic 4 He superfluids.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics of adiabatic melting of solid He4 in liquid He3

2019

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In the cooling concept by adiabatic melting, solid 4 He is converted to liquid and mixed with 3 He to produce cooling power directly in the liquid phase. This method overcomes the thermal boundary resistance that conventionally limits the lowest available temperatures in the helium fluids and hence makes it possible to reach for the temperatures significantly below 100 μK. In this paper we focus on the thermodynamics of the melting process, and examine the factors affecting the lowest temperatures achievable. We show that the amount of 3 He− 4 He mixture in the initial state, before the melting, can substantially lift the final temperature, as its normal Fermi fluid entropy will remain relatively large compared to the entropy of superfluid 3 He. We present the collection of formulas and parameters to work out the thermodynamics of the process at very low temperatures, study the heat capacity and entropy of the system with different liquid 3 He, mixture, and solid 4 He contents, and use them to estimate the lowest temperatures achievable by the melting process, as well as compare our calculations to the experimental saturated 3 He− 4 He mixture crystallization pressure data. Realistic expectations in the execution of the actual experiment are considered. Further, we study the cooling power of the process, and find the coefficient connecting the melting rate of solid 4 He to the dilution rate of 3 He.

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“…On the purely microscopic level, there has been the variational track -including the correlation-basis--functions theory [7]; and the perturbative track -including the Galitskii-Migdal-Feynman (GMF) and the Brueckner-Bethe-Goldstone (BBG) frameworks [8]. The perturbative track offers greater elegance and formal power; on the other hand, variational calculations appear to have enjoyed greater numerical success [9].…”

Section: Introductionmentioning

confidence: 99%

“…Al-Sugheir et al [8] studied the effect of hole-hole scattering on any possible fermion-fermion pairing in these systems by calculating the effective relative phase shifts, incorporating many-body effects based on both BBG and GMF formalisms. In the GMF formalism, the s-wave phase shift at zero relative momentum was −π and had a cusp at the Fermi momentum; while in the BBG formalism, this phase shift had zero values up to the Fermi momentum.…”

Section: Introductionmentioning

confidence: 99%

Weak³He Pairing in³He-He(II) Mixtures

et al. 2011

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In this paper a theoretical study of a possible phase transition in dilute 3 He-He(II) mixtures is presented using the Galitskii-Migdal-Feynman formalism. The effective scattering length is calculated from the GalitskiiMigdal-Feynman T -matrix, which is essentially the effective scattering amplitude dependent on the medium. It is found that at very low 3 He concentrations the s-wave effective scattering length for 3 He-He(II) varies discontinuously from positive to negative values at some critical concentration. This indicates a crossover from a regime with dimers to another with the Cooper pairs. The binding energy of the weakly-bound dimers 3 He2 is computed. The effective p-wave scattering lengths are calculated and compared to the effective s-wave scattering lengths at low and high concentrations. It is found that p-scattering has an important effect on the instability of these mixtures at concentrations x > 1%. Finally, the transport coefficients are computed and compared to the theoretical predictions of Fu and Pethick and the experimental results of König and Pobell.

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FERMI PAIRING IN DILUTE ³He-HeII MIXTURES

Cited by 16 publications

References 13 publications

Performance of Adiabatic Melting as a Method to Pursue the Lowest Possible Temperature in $$^{3}\hbox {He}$$ and $$^{3}\hbox {He}$$–$$^{4}\hbox {He}$$ Mixture at the $$^{4}\hbox {He}$$ Crystallization Pressure

Performance of Adiabatic Melting as a Method to Pursue the Lowest Possible Temperature in $$^{3}\hbox {He}$$ and $$^{3}\hbox {He}$$–$$^{4}\hbox {He}$$ Mixture at the $$^{4}\hbox {He}$$ Crystallization Pressure

Thermodynamics of adiabatic melting of solid He4 in liquid He3

Weak³He Pairing in³He-He(II) Mixtures

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FERMI PAIRING IN DILUTE 3He-HeII MIXTURES

Cited by 16 publications

References 13 publications

Performance of Adiabatic Melting as a Method to Pursue the Lowest Possible Temperature in $$^{3}\hbox {He}$$ and $$^{3}\hbox {He}$$–$$^{4}\hbox {He}$$ Mixture at the $$^{4}\hbox {He}$$ Crystallization Pressure

Performance of Adiabatic Melting as a Method to Pursue the Lowest Possible Temperature in $$^{3}\hbox {He}$$ and $$^{3}\hbox {He}$$–$$^{4}\hbox {He}$$ Mixture at the $$^{4}\hbox {He}$$ Crystallization Pressure

Thermodynamics of adiabatic melting of solid He4 in liquid He3

Weak3He Pairing in3He-He(II) Mixtures

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FERMI PAIRING IN DILUTE ³He-HeII MIXTURES

Weak³He Pairing in³He-He(II) Mixtures