Large Variety of the On-Site Order Parameters and Phase States in Quasi-2D HTSC Cuprates

Abstract

Starting with a minimal model in which the on-site Hilbert space is reduced to only three effective valence centers \({\text{CuO}}_{4}^{{7 - ,6 - ,5 - }}\) (nominally \({\text{C}}{{{\text{u}}}^{{1 + ,2 + ,3 + }}}\)), we present a unified approach to the description of variety of the local intra-unit-cell order parameters in high-T\(_{c}\) cuprates going beyond Zhang–Rice model and address recent experimental findings. Central point of the model implies the occurrence of unconventional on-site quantum superpositions of three valent states characterized by different hole occupation: \({{n}_{h}}\) = 0, 1, 2 for \({\text{C}}{{{\text{u}}}^{{1 + ,2 + ,3 + }}}\) centers, respectively, different conventional spin: s = 1/2 for \({\text{C}}{{{\text{u}}}^{{2 + }}}\) center and s = 0 for \({\text{C}}{{{\text{u}}}^{{1 + ,3 + }}}\) centers, and different orbital symmetry:\({{B}_{{1g}}}\) for the ground state of the \({\text{C}}{{{\text{u}}}^{{2 + }}}\) centers, \({{A}_{{1g}}}\) for the \({\text{C}}{{{\text{u}}}^{{1 + }}}\) centers, and the Zhang–Rice (ZR) \({{A}_{{1g}}}\) or more complicated low-lying non-ZR states for \({\text{C}}{{{\text{u}}}^{{3 + }}}\) center.