Ab initio low-energy effective Hamiltonians for the high-temperature superconducting cuprates Bi2Sr2CuO6, Bi2Sr2CaCu2O8, HgBa2CuO4, and CaCuO2

Abstract

We derive ab initio low-energy effective Hamiltonians (LEH) for high-temperature superconducting (SC) copper oxides Bi2Sr2CuO6 (Bi2201, Nℓ=1, Tcexp∼10K), Bi2Sr2CaCu2O8 (Bi2212, Nℓ=2, Tcexp∼84K), HgBa2CuO4 (Hg1201, Nℓ=1, Tcexp∼90K), and CaCuO2 (Ca11, Nℓ=∞, Tcexp∼110K), with substantially different values of experimental optimal SC transition temperature Tcexp and number Nℓ of laminated CuO2 planes between the two neighboring block layers. We apply the latest methodology of the multiscale ab initio scheme for correlated electron systems (MACE), and focus on the LEH consisting of one antibonding (AB) Cu3dx2−y2/O2pσ orbital centered on each Cu atom. We discuss prominent features of this LEH: (1) The ratio U/|t1| between the onsite effective Coulomb repulsion (ECR) U and amplitude of nearest-neighbor hopping t1 increases with Tcexp and Nℓ, consistently with the expected increase in d-wave SC correlation function Pdd with U/|t1|. One possible cause of the increase of U/|t1| with Nℓ is the replacement of apical O atoms by Cu atoms from neighboring CuO2 planes when Nℓ increases. Furthermore, we show that the increase in distance between Cu and apical O atoms decreases the effective screening (ES) defined as the screening by electrons outside of the LEH and increases U/|t1|. (2) For Hg1201 and Ca11, we examine the variation in U/|t1| with hole doping per AB orbital δ, and show that U/|t1| decreases when δ increases, which may partly account for the disappearance of SC when δ exceeds the optimal value in experiment. (3) For Nℓ≥2, offsite inter-CuO2 plane ECR is comparable to off-site intra-CuO2 plane ECR. We discuss contributions of inter-CuO2 plane ECR to both Pdd and the stability of the SC state.

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