Unconventional superconductivity and non-Fermi liquid behaviour of ε-iron at high pressure

We report further resistive measurements under pressure of samples of iron from multiple sources. The normal state resistivity of ε-iron varied as ρ₀ + AT^5/3 at low temperature over the entire superconducting pressure domain. The superconductivity could be destroyed by mechanical work, and was restored by annealing, demonstrating sensitivity to the residual resistivity ρ₀. There is a strong correlation between the ρ₀ and A coefficients and the superconducting critical temperature T_c. The critical field B_c2 corresponding to the maximum T_c was found to be 0.73 T, implying a coherence length of about 20 nm, i.e. slightly shorter than the electronic mean free path. Within the partial resistive transition there was a significant current dependence, with V(I) = a(I -I₀) + bI², and a ≫ b, possibly indicating flux-flow resistivity, even in the absence of an externally applied magnetic field.