Thermal expansion at low temperatures IV. Normal and superconducting lead

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 α_s = (1.30₀ ± 1₀) × 10⁻⁹ T ³, α_n = (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 C_e /∂ In V = 1.7 is computed from the linear term in α_n. 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