Glassy electrons at the first-order Mott metal-insulator transition

Abstract

The Mott metal-insulator transition remains one of the most scrutinized concepts in condensed matter physics. However, the kinetics of the charge carriers at the transition, involving both orbital and spin degrees of freedom, still remains poorly understood. A perfect platform to distinguish between the role of such competing interactions is strongly correlated oxides offering rich phase diagrams, which we use here to address the electron kinetics at the transition. We show a critical slowing down of the electron kinetics at the first-order Mott metal-insulator transition in the Ruddlesden-Popper oxide ${\mathrm{Ca}}_{3}{({\mathrm{Ru}}_{0.9}{\mathrm{Ti}}_{0.1})}_{2}{\mathrm{O}}_{7}$ using low-frequency noise in resistance fluctuations. A critical slowing down of the electron kinetics is manifested as an enhancement of noise by an order of magnitude at the transition with a large shift of the spectral weight to lower frequencies. The second spectrum of noise is frequency dependent, indicating the presence of correlated fluctuations which get suppressed under the application of a magnetic field. Our experiments provide compelling evidence of the formation of a spin-glass phase at the transition in these systems.