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Microscopic mechanism of high-temperature superconductivity revealed by ab initio studies on hole-doped multilayer cuprates HgBa2Ca2Cu3O8 under pressure

Ryui Kaneko1,* and Masatoshi Imada1,2,†

  • *Contact author: ryuikaneko@sophia.ac.jp
  • †Contact author: imada@g.ecc.u-tokyo.ac.jp

Phys. Rev. Research 8, 043024 – Published 8 October, 2026

DOI: https://doi.org/10.1103/qqvw-ltth

Abstract

Triple-layer cuprate superconductor HgBa2Ca2Cu3O8 (Hg1223) keeps the record of the highest superconducting (SC) critical temperature Tc∼134K among all the existing materials at ambient pressure. Tc further increases under pressure up to Tc∼160K, thereby holding the key to the realistic and comprehensive understanding of the cuprate superconductors, which is one of the grand challenges in physics. However, the microscopic mechanism of high Tc of Hg1223 remains to be elucidated. Here, we perform first-principles calculations of Hg1223 both at ambient and applied pressures by solving ab initio Hamiltonians with an accurate variational solver supplemented by a neural network. The pressure dependence of the calculated d-wave SC order parameter and estimated Tc shows a structure supporting a Tc peak around 30 GPa in quantitative agreement with the reported experimental indications. The origin of the strong SC amplitude of Hg1223 at ambient pressure compared to other cuprates is identified as strong local Coulomb repulsion U attributed to poorer screening of the Coulomb interaction in multilayer compounds. The origin of the further increase in Tc under pressure is ascribed to a unique interplay of three elements, namely, increased electron hopping t, decreased U, and more importantly, strongly reduced nonlocal Coulomb repulsion V with increasing pressure. The origin of Cooper pairing is identified as the emergent local attraction counterintuitively arising from the strong bare local repulsion U for Hg1223. It explains why Hg1223 shows the highest Tc among other cuprates, while the pairing mechanism is common in other cuprates as well. The emergent attraction is interpreted from “attraction from reduced repulsion,” originating from the release of the fluctuating doubly occupied sites characterized from the “false vacuum” in the Mott insulator to the double-occupation-free d-wave SC states caused by the carrier doping. This instantaneous and local attraction is in marked contrast with the case of the conventional BCS SC mediated by bosonic glues. The local attraction is consistent with the electron fractionalization supported in experimental analyses. The coexistence of SC and antiferromagnetic orders is also demonstrated as a characteristic feature of the multilayer system with self-doping in the underdoped region. The quantitative and microscopic understanding of the high Tc in Hg1223 provides a new perspective on the origin of the cuprate superconductivity and offers a new route explicitly using this channel of the emergent attraction for future superconductivity research aiming at designing and optimizing SC materials.

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