Dome structure in pressure dependence of superconducting transition temperature for HgBa_2Ca_2Cu_3O_8 – Studies by ab initio low-energy effective Hamiltonian

The superconducting (SC) cuprate HgBa_2Ca_2Cu_3O_8 (Hg1223) has the highest T_c^ opt≃ 138 K (the experimental SC transition temperature at optimal hole doping) among cuprates at ambient pressure P_ amb. T_c^ opt increases under pressure P and reaches 164 K at P_ opt≃ 30 GPa, then decreases with increasing P>P_ opt. To understand the microscopic origin of this dome-like P dependence of T_c^ opt, we consider the ab initio low-energy effective Hamiltonian (LEH) for the antibonding (AB) Cu3d_x^2-y^2/O2p_σ band. In the AB LEH for cuprates with N_ℓ≤ 2 laminated CuO_2 planes between block layers, it was proposed that T_c^ opt≃ 0.16|t_1|F_ SC, where t_1 is the nearest neighbor hopping and the SC order parameter F_ SC at optimal hole doping mainly depends on u=U/|t_1| (U is the onsite effective Coulomb repulsion): F_ SC is maximal at u_ opt≃ 8.5 and decreases sharply with decreasing u for uP_ opt, the decrease in T_c^ opt is accounted for by (II): The rapid decrease in F_ SC with decreasing u for u更多