Shot noise and universal Fano factor as a characterization of strongly correlated metals

Shot noise measures out-of-equilibrium current fluctuations and is a powerful tool to probe the nature of current-carrying excitations in quantum systems. Recent shot-noise measurements in the heavy-fermion strange metal <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>YbRh</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi>Si</a:mi><a:mn>2</a:mn></a:msub></a:mrow></a:math> exhibit a strong suppression of the Fano factor (<b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mi>F</b:mi></b:math>)—the ratio of the current noise to the average current in the dc limit. This system is representative of metals in which electron correlations are extremely strong. Here we carry out the first theoretical study on the shot noise of diffusive metals in the regime of strong correlations. A Boltzmann-Langevin equation formulation is constructed in a quasiparticle description in the presence of strong correlations. We find that <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>F</c:mi><c:mo>=</c:mo><c:msqrt><c:mn>3</c:mn></c:msqrt><c:mo>/</c:mo><c:mn>4</c:mn></c:mrow></c:math> in such a correlation regime. Thus, we establish the aforementioned Fano factor as universal to Fermi liquids, and we show that the Fano factor suppression observed in experiments on <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:msub><d:mi>YbRh</d:mi><d:mn>2</d:mn></d:msub><d:msub><d:mi>Si</d:mi><d:mn>2</d:mn></d:msub></d:mrow></d:math> necessitates a loss of the quasiparticles. Our work opens the door to systematic theoretical studies of shot noise as a means of characterizing strongly correlated metallic phases and materials. Published by the American Physical Society 2024