Influence of the Rutgers Relation on underdoped cuprate properties*

Within the extended Layered Boson-Fermion Model of Superconductivity [1,2] the Rutgers Relation, which relates the diference between the normal and the superconducting isobaric specific heats with the thermodynamic critical field, is combined with the first-principles relation of the critical field derivative as well as with the penetration and coherence lengths to get a novel expression for the penetration length λ(T), which is more suitable for high temperature superconductors, as we have seen after applying it to underdoped cuprate superconductors YBa₂Cu₃O_6+x.
We compare our current results for the penetration length and the normalized superfluid density as functions of temperature as well as of doping x, with experiments and our previously reported results, obtaining a substantial improvement.
[1] P. Salas, M. Fortes, M.A. Solís and F.J. Sevilla, Physica C 534, 37 (2016).
[2] P. Salas, M.A. Solís, M. Fortes and F.J. Sevilla, Int. J. of Mod. Phys. B 31, 1750100 (2017).