title: Self-optimized superconductivity attainable by interlayer phase separation at cuprate interfaces.
abstract: Stabilizing superconductivity at high temperatures and elucidating its mechanism have long been major challenges of materials research in condensed matter physics. Meanwhile, recent progress in nanostructuring offers unprecedented possibilities for designing novel functionalities. Above all, thin films of cuprate and iron-based high-temperature superconductors exhibit remarkably better superconducting characteristics (for example, higher critical temperatures) than in the bulk, but the underlying mechanism is still not understood. Solving microscopic models suitable for cuprates, we demonstrate that, at an interface between a Mott insulator and an overdoped nonsuperconducting metal, the superconducting amplitude is always pinned at the optimum achieved in the bulk, independently of the carrier concentration in the metal. This is in contrast to the dome-like dependence in bulk superconductors but consistent with the astonishing independence of the critical temperature from the carrier density x observed at the interfaces of La2CuO4 and La2-x Sr x CuO4. Furthermore, we identify a self-organization mechanism as responsible for the pinning at the optimum amplitude: An emergent electronic structure induced by interlayer phase separation eludes bulk phase separation and inhomogeneities that would kill superconductivity in the bulk. Thus, interfaces provide an ideal tool to enhance and stabilize superconductivity. This interfacial example opens up further ways of shaping superconductivity by suppressing competing instabilities, with direct perspectives for designing devices.
authors.affiliation: Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Misawa
authors.affiliation: Centre de Physique Théorique, École Polytechnique, CNRS, Université Paris-Saclay, F-91128 Palaiseau, France.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Nomura
authors.affiliation: Centre de Physique Théorique, École Polytechnique, CNRS, Université Paris-Saclay, F-91128 Palaiseau, France.
authors.forename: Silke
authors.initials: S
authors.lastname: Biermann
authors.affiliation: Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Masatoshi
authors.identifier: 0000-0002-5511-2056
authors.initials: M
authors.lastname: Imada
mesh_terms: D003300:Copper / Q000737:chemistry; D007811:Lanthanum / Q000737:chemistry; D008962:Models, Theoretical; D010087:Oxides / Q000737:chemistry; D000072176:Superconductivity; D013696:Temperature
chemical_list: C519316:La2CuO4; D010087:Oxides; D007811:Lanthanum; D003300:Copper
keywords: Thin films; copper oxide superconductors; d-wave symmetry; doped Mott insulator; first-principles calculation; inhomogeneity; interface; phase separation; self-organization; variational Monte Carlo method