Nonthermal excitonic condensation near a spin-state transition

TL;DR

This paper demonstrates that nonthermal excitonic condensates can be induced near a spin-state transition in a two-orbital Hubbard model through crystal-field quenches, leading to long-lived states beyond equilibrium possibilities.

Contribution

It introduces a mechanism for creating nonthermal excitonic condensates via dynamical quenches near a spin-state transition, supported by an effective pseudo-spin model.

Findings

Quenches induce excitonic condensation above equilibrium transition temperatures.

Identification of a dynamical phase transition leading to long-lived nonthermal states.

Effective pseudo-spin model explains the nonthermal condensate formation.

Abstract

We consider a two-orbital Hubbard model with Hund coupling and crystal-field splitting and show that in the vicinity of the high-spin/low-spin transition, crystal-field quenches can induce an excitonic condensation at initial temperatures above the highest ordering temperature in equilibrium. This condensation is the effect of an increase in the spin entropy and an associated cooling of the effective electronic temperature. We identify a dynamical phase transition and show that such quenches can result in long-lived nonthermal excitonic condensates which have no analogue in the equilibrium phase diagram. The results are interpreted by means of an effective pseudo-spin model.