What Can we Learn from Nonequilibrium Response of a Strange Metal?

We critically address the recent experiment by L. Chen et al. [Science 382, 907 (2023)] on nonequilibrium transport and noise in a strange metal YbRh₂Si₂ patterned into the nanowire shape. In the long device, resistivity, differential resistance and current noise data seem to be consistent allowing us to extract electron–phonon coupling and the temperature dependence of electron–phonon scattering length. The obtained values can be reconciled with the experimental data for the short device only assuming the significant contact resistance. We discuss its possible origin as due to the current redistribution between YbRh₂Si₂ and its gold covering, and reveal that this redistribution contact resistance should be proportional to the YbRh₂Si₂ resistivity. We also discuss some subtleties of the noise measurements. Overall, neglecting electron–phonon energy relaxation even in the shortest devices is arguable so that the observed shot noise suppression can hardly be attributed to the failure of quasiparticle concept.