Emerging superconductivity hidden beneath charge-transfer insulators

Abstract

In many of today's most interesting materials, strong interactions prevail upon the magnetic moments, the electrons, and the crystal lattice, forming strong links between these different aspects of the system. Particularly, in two-dimensional cuprates, where copper is either five- or six-fold coordinated, superconductivity is commonly induced by chemical doping which is deemed to be mandatory by destruction of long-range antiferromagnetic order of 3d9 Cu2+ moments. Here we show that superconductivity can be induced in Pr2CuO4, where copper is four-fold coordinated. We induced this novel quantum state of Pr2CuO4 by realizing pristine square-planar coordinated copper in the copper-oxygen planes, thus, resulting in critical superconducting temperatures even higher than by chemical doping. Our results demonstrate new degrees of freedom, i.e., coordination of copper, for the manipulation of magnetic and superconducting order parameters in quantum materials.

DMFT Study on the Electron–hole Asymmetry of the Electron Correlation Strength in the High Tc Cuprates

“…However, recent experimental studies have shown that, in the electron-doped systems, the electron correlation strength is not so strong that even very lightly doped samples exhibit superconductivity if they are properly annealed and the antiferromagnetism is suppressed. Some of these studies suggest that superconductivity persists even with no electron doping, [1][2][3] while others show presence of antiferromagnetic long range order in the lightly doped regime, 4,5) so that the issue is still controversial. It was also shown experimentally that the "pseudo gap", [6][7][8][9][10] a prominent feature of the cuprates, disappears if the antiferromagnetism is suppressed.…”

At the interface between electron and hole-doped cuprates

“…Raman spectroscopy and infrared transmission measurements suggest that the effect of the reduction is even doping dependent; for low doping mainly apical oxygen appears to be removed and near optimal doping, oxygen is mostly removed from the CuO 2 planes [46,47]. Recent experiments by Krockenberger et al suggest that the reduction process might be a two step process [41]. The authors claim that a high temperature low oxygen pressure annealing removes oxygen from the crystal (Pr 2-x Ce x CuO 4 thin films in this case), mainly from the CuO 2 planes; a second vacuum annealing at a lower temperature allows apical oxygen that is not removed in the first annealing to fill the vacancies in the CuO 2 planes.…”

“…In most cases Ce doping is used as a source of charge carriers and a certain doping level (x = 0.1 -0.18) is required to achieve superconductivity [29], but undoped compounds have also been made superconducting simply by reduction [39][40][41]. In the latter case, superconductivity is achieved by a two-step annealing procedure [41] or by isovalent substitution of La by Y in La 2 CuO 4 [39,40].…”

“…The reduction removes oxygen from the CuO 2 planes, breaking the antiferromagnetic order [41,[46][47][48][49].…”

“…In the latter case, superconductivity is achieved by a two-step annealing procedure [41] or by isovalent substitution of La by Y in La 2 CuO 4 [39,40].…”