Correlation-driven charge and spin fluctuations in LaCoO$_3$

TL;DR

This study uses advanced computational methods to reveal that charge and spin fluctuations, involving multiple electronic configurations, are crucial in understanding the spin transition in LaCoO$_3$, highlighting the importance of electronic correlations.

Contribution

It demonstrates the role of charge fluctuations and multiple electronic states in LaCoO$_3$'s spin transition using DFT+DMFT and quantum Monte Carlo methods.

Findings

Charge fluctuations induce mixed $d^5$ and $d^7$ states.

Significant contributions of $d^5$ and $d^7$ states to LS-HS transition.

Kinetic energy gain from charge fluctuations lowers total energy.

Abstract

The spin transition in LaCoO$_3$ has been investigated within the density-functional theory + dynamical mean-field theory formalism using continuous time quantum Monte Carlo. Calculations on the experimental rhombohedral atomic structure with two Co sites per unit cell show that an independent treatment of the Co atoms results in a ground state with strong charge fluctuations induced by electronic correlations. Each atom shows a contribution from either a $d^5$ or a $d^7$ state in addition to the main $d^6$ state. These states play a relevant role in the spin transition which can be understood as a low spin-high spin (LS-HS) transition with significant contributions ($\sim$ $10$ %) to the LS and HS states of $d^5$ and $d^7$ states respectively. A thermodynamic analysis reveals a significant kinetic energy gain through introduction of charge fluctuations, which in addition to the potential energy reduction lowers the total energy of the system.