Electron–phonon coupling constant and BCS ratios in LaH10−y doped with magnetic rare-earth element

Abstract

Abstract Stoichiometric near-room-temperature superconductors (NRTS) (for instance, H3S and LaH10) exhibit a high ground-state upper critical field, B c2(0) ⩾ 100 T, so that the magnetic phase diagram in these materials cannot be measured in non-destructive experiments. However, (Semenok et al 2022 Adv. Mater.) proposed the idea of exploring the full magnetic phase diagram in NRTS samples, in which the superconducting order parameter is suppressed by magnetic element doping. If the elements areuniformly distributed in the material, then the theory of electron–phonon mediated superconductivity predicts the suppression of the order parameter in a 3D s-wave superconductor. (Semenok et al 2022 Adv. Mater.) experimentally proved this idea by substituting lanthanum with the magnetic rare-earth neodymium in (La1−x Nd x )H10−y . As a result, the transition temperature in (La1−x Nd x )H10−y (x = 0.09) was suppressed to T c ∼ 120 K, and the upper critical field decreased to B c2(T= 41 K) = 55 T. While the exact hydrogen content should be further established in the (La1−x Nd x )H10−y (x = 0.09) (because similar T c suppression was observed in hydrogen-deficient LaH10−y samples reported by Drozdov et al (2019 Nature 569 528)), a significant part of the full magnetic phase diagram for the (La1−x Nd x )H10−y (x = 0.09) sample was measured. Here, we analyzed the reported (Semenok et al 2022 Adv. Mater.) magnetoresistance data for (La1−x Nd x )H10−y (x = 0.09) compressed at P = 180 GPa and deduced: (a) Debye temperature, T θ = 1156 ± 6 K ; (b) the electron–phonon coupling constant, λ e − ph = 1.65 ± 0.01 ; (c) the ground-state superconducting energy gap, Δ 0 = 20.2 ± 1.3 meV ; (d) the gap-to-transition temperature ratio, 2 Δ 0 k B T c = 4.0 ± 0.2 ; and (e) the relative jump in specific heat at transition temperature, Δ C γ T c = 1.68 ± 0.15 . The deduced values indicate that (La1−x Nd x )H10−y (x = 0.09; P = 180 GPa) is a moderately strongly coupled s-wave superconductor.