Emergent Behavior in Strongly Correlated Electron Systems

TL;DR

This paper discusses the shift from reductionist to emergent approaches in understanding strongly correlated electron systems, emphasizing phenomenology and principles derived from experiments to inform microscopic models.

Contribution

It highlights the paradigm change towards an emergent, phenomenology-driven approach in studying SCES and related systems, focusing on organizing principles and their applications.

Findings

Identification of key organizing principles for emergent phenomena

Application of random phase approximation to SCES

Insights into heavy electron behavior and unconventional superconductivity

Abstract

I describe early work on strongly correlated electron systems [SCES] from the perspective of a theoretical physicist who, while a participant in their reductionist top- down beginnings, is now part of the paradigm change to a bottom-up "emergent" approach with its focus on using phenomenology to find the organizing principles responsible for their emergent behavior disclosed by experiment---and only then constructing microscopic models that incorporate these. After considering the organizing principles responsible for the emergence of plasmons, quasiparticles, and conventional superconductivity in SCES, I consider their application to three of SCES's sister systems, the helium liquids, nuclei, and the nuclear matter found in neutron stars. I note some recent applications of the random phase approximation and examine briefly the role that paradigm change is playing in two central problems in our field: understanding the emergence and subsequent behavior of heavy electrons in Kondo lattice materials; and finding the mechanism for the unconventional superconductivity found in heavy electron, organic, cuprate, and iron-based materials.