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.