Heat capacity of mixtures of – confined to coupled boxes

We have measured the heat capacity of helium mixtures confined to lithographically created cylindrical boxes whose height, 1.08 μm , equals their diameter. The specific heat at constant concentration x, C px , is renormalized due to the 3 He impurity. Thus, in order to observe critical behavior, a conversion must be made to a specific heat at constant φ=μ 3 −μ 4 , C pφ . The confined system's specific heat, near it's maximum, has values which rise above the bulk system's specific heat at the same temperature. This is unexpected and is true for both Cpx and Cpφ. This enhancement, not observed with pure 4 He , becomes more dramatic as x and the correlation length increase. The shift of the maximum with x is much larger for the boxes than for 2D confined mixtures. These observations might be related to a “band structure” effect associated with the 18.5 nm channels which connect the cylinders.