Nonlocal Coulomb interaction and spin-freezing crossover as a route to valence-skipping charge order

Siheon Ryee,Sangkook Choi,Myung Joon Han,Patrick Sémon

doi:10.1038/s41535-020-0221-9

Abstract

Multiorbital systems away from global half-filling host intriguing physical properties promoted by Hund’s coupling. Despite increasing awareness of this regime dubbed Hund’s metal, effect of nonlocal interaction is still elusive. Here we study a three-orbital model with 1/3 filling (two electrons per site) including the intersite Coulomb interaction (V). Using the GW plus extended dynamical mean-field theory, the valence-skipping charge order transition is shown to be driven by V. Most interestingly, the instability to this transition is significantly enhanced in the spin-freezing crossover regime, thereby lowering the critical V to the formation of charge order. This behavior is found to be closely related to the population profile of the atomic multiplet states in the spin-freezing regime. In this regime, maximum spin states are dominant in each total charge subspace with substantial amount of one- and three-electron occupations, which leads to almost equal population of one- and the maximum spin three-electron state. Our finding unveils another feature of the Hund’s metal and has potential implications for the broad range of multiorbital systems as well as the recently discovered charge order in iron pnictides.

Highlights

Classifying a number of phases and understanding their relevance to different energy scales has been a central theme of condensed matter physics
By employing the state-of-the-art GW plus extended dynamical mean-field theory (GW+EDMFT) adapted to multiorbital models, we demonstrate that the valence-skipping charge order (CO)
One can confirm that this CO transition is driven by V (compare Fig. 3b with Fig. 3a; see Supplementary Note 3 for χ(k, iν0) at V = 0)

Summary

INTRODUCTION

Classifying a number of phases and understanding their relevance to different energy scales has been a central theme of condensed matter physics. A purely intra-atomic origin, namely, the anisotropic orbital-multipole scattering, was suggested to be the key ingredient for such valence-skipping phenomena[28] This phase has potential implications for the electron pairing mechanisms of unconventional superconductivity[28,33]. By employing the state-of-the-art GW plus extended dynamical mean-field theory (GW+EDMFT) adapted to multiorbital models, we demonstrate that the valence-skipping CO is driven by intersite nonlocal Coulomb repulsion V, and the instability to this phase is significantly enhanced in the spinfreezing crossover regime. This enhancement is shown to be related to the local multiplet population profile. This route to the valence-skipping is distinctive from the anisotropic orbitalmultipole scattering mechanism[28]

RESULTS AND DISCUSSION

METHODS

CODE AVAILABILITY