fabrication-uniform-nanoscale-cavities-via-silicon-direct-wafer

Fabrication of Uniform Nanoscale Cavities via Silicon Direct Wafer Bonding

Measurements of the heat capacity and superfluid fraction of confined 4He have been performed near the lambda transition using lithographically patterned ...

The State University of New York at Buffalo

We have measured the heat capacity of (3)He-(4)He mixtures confined in films of thickness 48.3 and 986.9 nm. The confinement is defined by direct bonding of two silicon wafers. The heat capacity is measured using an ac technique and then transformed to correct for exponent renormalization effects. The data address the expected universal critical behavior along the lambda line as function of (3)He concentration. We discuss the results of several analyses of the data, and we show that a universal collapse can be achieved for all the mixtures. However, this is on a locus which differs from that of the pure system. An alternative analysis is also presented which yields collapse of all the data under certain assumptions. We believe these data are the first to test universality of finite-size scaling for the specific heat along a locus of transitions.

Universality and finite-size scaling of the specific heat of 3He-4He mixtures.

We report measurements of the superfluid fraction ρ(s)/ρ and specific heat c(p) near the superfluid transition of 4He when confined in an array of (2  μm)3 boxes at a separation of S=2  μm and coupled through a 32.5 nm film. We find that c(p) is strongly enhanced when compared with data where coupling is not present. An analysis of this excess signal shows that it is proportional to the finite-size correlation length in the boxes ξ(t,L), and it is measurable as far as S/ξ∼30-50. We obtain ξ(0,L) and the scaling function (within a constant) for ξ(t,L) in an L3 box geometry. Furthermore, we find that ρ(s)/ρ of the film persists a full decade closer to the bulk transition temperature T(λ) than a film uninfluenced by proximity effects. This excess in ρ(s)/ρ is measurable even when S/ξ>100, which cannot be understood on the basis of mean field theory.

Article	Year
Universality and finite-size scaling of the specific heat of 3He-4He mixtures. Physical review letters\| PubMed ID: 16241816	2005
Critical point coupling and proximity effects in 4He at the superfluid transition. Physical review letters\| PubMed ID: 22861866	2012

Francis M. Gasparini

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