Identifying mechanisms of quantum nematic transitions from the dynamic susceptibility

Abstract

Several strongly correlated electronic materials, such as FeSe, are thought to manifest quantum critical transitions to an electronic nematic state. In my talk, I will discuss an interesting feature of the nematic QCP: its anisotropic (quadrupolar) nature implies the appearance of dynamical fluctuations at finite frequencies but very long spatial scales. These fluctuations encode information on the driving mechanism of the nematic transition: whether it involves an external degree of freedom, such as spin fluctuations, coupled to the electronic charge, or internal charge degrees of freedom (a Pomeranchuk instability). I will show that Raman data for FeSe1-xSx agrees with the hypothesis of a Pomeranchuk instability. Finally, I will also describe how these nematic critical fluctuations are ‘shaped’ by conservation laws (which are constraints on long spatial scales), implying a fascinating interplay between classical and quantum scales.