Enhanced Superconducting Gap in the Outer CuO2 Plane of the Trilayer Cuprate (Hg, Re)Ba2Ca2Cu3 O8+δ

Abstract

We report the first observation of a momentum-resolved superconducting gap in the Hg-based trilayer cuprate, which holds the highest record of superconducting transition temperature (Tc) at ambient pressure. By angle-resolved photoemission spectroscopy utilizing a microfocused beam, clear quasiparticle dispersions originating from the inner and outer CuO2 planes (IP and OP, respectively) were separately identified. The magnitude of the superconducting gap for the IP was comparable to that of the Bi-based trilayer cuprate with a lower Tc. In contrast, the superconducting gap for the OP was significantly larger than that of the Bi-based one. While strong pairing in the IP has been highlighted as the key element of trilayer cuprates, the present results suggest that the enhanced pairing energy in the OP is essential for the highest Tc at ambient pressure realized in the Hg-based trilayer cuprate.