Thermal expansion at low temperatures IV. Normal and superconducting lead

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Abstract
Measurements are reported of the linear thermal expansion of lead between 1.3° and 12°K. At the lowest temperature the contraction in changing from the superconducting to normal state is about 17 parts in 108, in fair agreement with the data of Olsen and Rohrer. The linear expansion coefficients below 4°K may be represented by αs = (1.300 ± 10) × 10−9 T 3, αn = (2.0 ± 0.3) × 10−9 T + (1.65 ± 0.10) × 10−9 T 3 per deg K. The Grüneisen parameter γ = 3αVK/C has a value of 2.7 near 10°K. At the lowest temperatures a value γ (electronic) = ∂ In Ce /∂ In V = 1.7 is computed from the linear term in αn. The pressure dependence of the critical field H c is deduced to be (∂H c/∂p) T ≃ −[7.3 + 4.4(T/T c)2] × 10−9 oe dyn−1 cm2