Randomness and Strangeness of Non-Fermi Liquids

Strange metals represent one of the long-standing challenges in the theory of correlated electron systems. Understanding the low-energy transport properties of these materials through microscopic models has proven to be a consistently difficult task due to the presence of strong interactions and the lack of well-defined quasiparticles.

We have constructed a kinetic theory applicable to the strange metal state, by combining the large-N analysis of the recently developed two-dimensional Yukawa-Sachdev-Ye-Kitaev model [Science 381, 790] with Keldysh field theory. The result takes the form of a closed kinetic equation for fermions and quantum critical bosons.

The existence of a kinetic equation enables us to investigate the properties of collective phenomena in strange metals using the analytical tools developed for Fermi liquids. The kinetic theory we present is applicable to various symmetry groups and serves as a powerful framework for exploring a range of low-energy effects in strange metals, including but not limited to nonlinear responses to electric fields, thermalization of effective bosonic degrees of freedom, electron thermalization, and sound attenuation.