Apical charge flux-modulated in-plane transport properties of cuprate superconductors

For copper-based superconductors, the maximum superconducting transition temperature, T_c,max, of different families measured from experiments can vary by an order of magnitude from 38 K in La₂CuO₄ to 135 K in HgBa₂Ca₂Cu₃O₈ at optimal hole doping concentration. We demonstrate herein, using ab initio computations, a new trend suggesting that the cuprates with stronger out-of-CuO₂-plane chemical bonding between the apical anion (O, Cl) and apical cation (e.g. La, Hg, Bi, Tl) are generally correlated with higher T_c,max in experiments. We then show the underlying fundamental phenomena of coupled apical charge flux and lattice dynamics when the apical oxygen oscillates vertically. This triggers the charge flux among the apical cation, apical anion and the in-plane CuO₄ unit. The effect not only dynamically modulates the site energy of the hole at a given Cu site to control the in-plane charge transfer energy, but also can modulate the in-plane hole hopping integral in a dynamic way by the cooperative apical charge fluxes.

Reference: Physical Review Letters, 121, 157001 (2018)