Fig. 2: Strange metal behavior of YbRh₂Si₂ and ¹⁷⁴YbRh₂Si₂.

a, b Temperature-dependent electrical resistivity at the quantum critical field of 60 mT applied within the tetragonal a-a plane. Superconductivity develops out of a strange metal ρ ~ T normal state. The parameters of the linear-in-T fits are given in Table 1. c Electrical resistivity exponent ϵ of the non-Fermi liquid form \(\rho =\rho_{0}^{\prime} +A^{\prime} {T}^{\epsilon }\), determined as \(\epsilon ={{{\rm{d}}}}{{{\mathrm{ln}}}}\,{{\Delta }}\rho /{{{\rm{d}}}}{{{\mathrm{ln}}}}\,T\), shown together with literature data up to high temperatures¹⁵. This establishes linear-in-T resistivity, evidenced by ϵ = 1 ± 0.05, over 3.5 orders of magnitude in temperature. Note that this presentation visualizes the temperature dependence of the exponent with great sensitivity, and that the error bar of ±0.05 corresponds to a high precision in the exponent’s closeness to the value of 1 (for comparison see, e.g., Fig. 12 of ref. ⁸).