Excited state quantum phase transitions in many-body systems

TL;DR

This paper investigates excited state quantum phase transitions in many-body systems, revealing their universal features across bosonic and fermionic models with pairing interactions, and analyzing their finite-size scaling behavior.

Contribution

It provides a detailed characterization of excited state quantum phase transitions and demonstrates their universality in various many-body models.

Findings

Excited state QPTs show singularities in spectra and wave functions.

Finite-size scaling behavior is determined at the mean field level.

Transitions are universal in models with pairing interactions.

Abstract

Phenomena analogous to ground state quantum phase transitions have recently been noted to occur among states throughout the excitation spectra of certain many-body models. These excited state phase transitions are manifested as simultaneous singularities in the eigenvalue spectrum (including the gap or level density), order parameters, and wave function properties. In this article, the characteristics of excited state quantum phase transitions are investigated. The finite-size scaling behavior is determined at the mean field level. It is found that excited state quantum phase transitions are universal to two-level bosonic and fermionic models with pairing interactions.