Causal relation between Pr-site distortions and mixed Pr valence in PrBa2Cu3O7

Ascertain the causal relationship between the in-plane Pr-site distortion associated with the quasi-commensurate Q1=(δ1,0,0) super-lattice and the mixed Pr3+/Pr4+ valence arising from Pr 4f–O 2p hybridization (Fehrenbacher–Rice state) in PrBa2Cu3O7, determining whether the structural distortion drives the hybridization and mixed valence or whether the hybridization induces the distortion, and characterize the mechanism linking these two phenomena.

Background

The paper identifies two distinct ordering vectors in Y1−xPrxBa2Cu3O6+y: a quasi-commensurate Q1=(δ1,0,0) order that resonates at the Pr and out-of-plane Cu sites, and a weaker, temperature-dependent Q2=(δ2,0,1/2) order resonating at the in-plane Cu site, interpreted as a charge-density wave. The Q1 order is strongest in PrBa2Cu3O7 (PBCO) and is interpreted as a Pr-related super-lattice structure with in-plane Pr distortions.

Within symmetry analysis, several orthorhombic and monoclinic subspace groups are allowed for the observed ordering vector, and in all cases in-plane Pr distortion modes are present. However, the authors note that the causal connection between these Pr-site distortions and the mixed Pr valence due to oxygen hybridization (a key ingredient of the Fehrenbacher–Rice scenario) is not established, motivating a focused investigation of how structural and electronic hybridization effects are intertwined in PBCO.