Inter- to intra-layer resistivity anisotropy of NdFeAs(O,H) with various hydrogen concentrations

With molecular beam epitaxy and a topotactic chemical reaction, we prepared NdFeAs(O,H) epitaxial thin films with various hydrogen concentrations on 5 degrees vicinal-cut MgO substrates. By measuring the resistivities along the longitudinal and transversal directions, the ab-plane and the c-axis resistivities (rho(ab) and rho(c)) were obtained. The resistivity anisotropy gamma(rho) rho(c)/rho(ab) of NdFeAs(O,H) with various hydrogen concentrations was compared with that of NdFeAs(O,F). At the H concentrations which led to superconducting transition temperatures T-c over 40 K, gamma(rho) recorded similar to 100-150 at 50 K. On the other hand, a low gamma(rho) value of 9 was observed with the highest-doped sample. The exponent beta of the ab-plane resistivity obtained by fitting a power-law expression rho(ab)(T) = rho(0) + AT(beta) to the data was close to unity down to a low temperature in the vicinity where the second antiferromagnetic phase locates, which may be related to the quantum critical point discussed at the overdoped side of the phase diagram.

Automated summary

Resistivity anisotropy of NdFeAs(O,H) thin films with different hydrogen concentrations was studied, showing higher γ(ρ) values at higher hydrogen concentrations and lower γ(ρ) value for the highest doped sample. The exponent β of the ab-plane resistivity fitting was close to unity, indicating the presence of a quantum critical point near the second antiferromagnetic phase.