Fig. 5: Power law exponent analysis for theory and experimental data.

a Evolution of the exponent with field from fits to the theoretical response for different gap structures of the form \({{\Delta }}(\phi ,T)={{{\Delta }}}_{0}(T)(| \cos (2\phi )| +\eta )\) and varying impurity concentration Γ (see Supplementary Note 6 for details about the calculations). b–d Experimental response from CeCoIn₅, LaFePO and KFe₂As₂ respectively. The exponent n is extracted from fits to \({\lambda }_{0}^{2}/{[{\lambda }_{0}+{{\Delta }}\lambda (T)]}^{2}=1-A{T}^{n}\) with upper T limit of 300 mK for CeCoIn₅ and KFe₂As₂, and up to 400 mK for LaFePO. The values assumed for λ₀ were 190 nm for CeCoIn₅⁴⁰, 240 nm for LaFePO¹³ and 200 nm for KFe₂As₂⁴¹. For the fits, to the theoretical response in (a) an upper limit of T/T_c = 0.1 was used. The error bars are the standard error deduced from the fit including a small contribution from the uncertainty in the background determination.