Superfluid density for underdoped cuprates

Within the extended Layered Boson-Fermion Model of superconductivity for underdoped cuprates [1, 2], we obtain the superfluid density ρ(T) combining: the difference between superconducting and normal isobaric specific heat ?C_p(T) = C^s_p(T) -Cⁿ_p(T); the thermodynamic critical field H_c(T), both as functions of temperature; and the improved Rutgers Relation after including the second derivative of H_c(T). In this way, we obtain a curve for the penetration length λ(T) more suitable for underdoped cuprates YBa₂Cu₃O_6+x , which is needed for the calculation of ρ(T)/ρ(0) = (λ(0)/λ(T))².

Our current results show the linear behaviour for low temperatures which is observed in the experimental data as well as a substantial improvement compared with our previous results.

[1] P. Salas, et al.,Physica C 534, 37 (2016).

[2] P. Salas, et al., Int. J. of Mod. Phys. B 31, 1750100 (2017).