1. Fig. 4 Superconductivity gap and specific heat jump.
Superconductivity gap and specific heat jump. (A) Temperature dependence of the 87Rb (tetrahedral site) spin-lattice relaxation rate, 1/87T1, normalized to its Tc value for RbxCs3−xC60 (0.35 ≤ x ≤ 3). Solid lines through the points are fits to the gap equation (see text). Dashed lines mark 2∆0/kBTc slopes between 3.5 and 6.5. (B) Left: Temperature dependence of specific heat, C, measured in zero magnetic field for RbxCs3−xC60 (x = 0.5, 1, 2, 3). The solid lines show the normal-state specific heat, Cn, for x = 0.5 and 3 obtained in the following way: the specific heat of pristine C60 was first subtracted from the total specific heat; the excess specific heat was then fitted at T > Tc by a combined Debye and Einstein term to obtain the background phonon contribution due to the C603−–C603− and alkali–C603− vibrational modes and extrapolated to temperatures below Tc (fig. S15). Right: Temperature dependence of the electronic specific heat measured in zero magnetic field divided by temperature, (C – Cn)/T (middle panel) for underexpanded and optimally expanded Na2CsC60,K3C60, and RbxCs3−xC60 (1 ≤ x ≤ 3) and (right panel) for overexpanded RbxCs3−xC60 (0.35 ≤ x < 1).
Ruth H. Zadik et al. Sci Adv 2015;1:e
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