Shot noise indicates the lack of quasiparticles in a strange metal

Understanding of strange metal properties, observed in materials from the high-temperature superconductors to heavy fermion metals and van der Waals structures, is an outstanding challenge. In conventional metals, current is carried by quasiparticles with charge of magnitude e, and while it has been suggested that quasiparticles are absent in strange metals, direct experimental evidence is lacking. We examine short, diffusive nanowires of the heavy fermion strange metal YbRh₂Si₂ and discover strongly suppressed shot noise compared to conventional metals. In contrast, shot noise measurements in short, diffusive gold nanowires are consistent with theoretical expectations for Fermi liquids. Using Johnson-Nyquist noise measurements in long wires, we find an electron-phonon coupling in this material comparable to that of gold, confirming that the suppression of noise seen in the strange metal samples is not due to electron-phonon effects. Shot noise probes the effective charge, or the granularity of the current-carrying excitations. With no other known mechanism to suppress the shot noise, the experimentally observed suppression implies that the current is not carried by well-defined quasiparticles in YbRh₂Si₂. Our work sets the stage for similar studies on other strange metals to test the universality of this result, and for future experiments at lower temperatures to examine the shot noise as the material is field-tuned between the Fermi liquid and strange metal regimes.