Spin correlations in the electron-doped high-transition-temperature superconductor Nd{2-x}Ce{x}CuO{4+/-delta}

TL;DR

This study investigates the evolution of antiferromagnetic spin correlations in electron-doped Nd{2-x}Ce{x}CuO{4+/-delta} superconductors, revealing a magnetic quantum critical point and linking pseudogap phenomena to spin correlation buildup.

Contribution

It provides new inelastic neutron-scattering data showing that long-range antiferromagnetism and superconductivity likely do not coexist, and identifies a quantum critical point in electron-doped cuprates.

Findings

Antiferromagnetism extends further with doping in electron-doped cuprates.

Superconductivity appears at a quantum critical point where antiferromagnetism diminishes.

Pseudogap phenomena are linked to the buildup of spin correlations.

Abstract

High-transition-temperature (high-Tc) superconductivity develops near antiferromagnetic phases, and it is possible that magnetic excitations contribute to the superconducting pairing mechanism. To assess the role of antiferromagnetism, it is essential to understand the doping and temperature dependence of the two-dimensional antiferromagnetic spin correlations. The phase diagram is asymmetric with respect to electron and hole doping, and for the comparatively less-studied electron-doped materials, the antiferromagnetic phase extends much further with doping [1, 2] and appears to overlap with the superconducting phase. The archetypical electron-doped compound Nd{2-x}Ce{x}CuO{4\pm\delta} (NCCO) shows bulk superconductivity above x \approx 0.13 [3, 4], while evidence for antiferromagnetic order has been found up to x \approx 0.17 [2, 5, 6]. Here we report inelastic magnetic neutron-scattering measurements that point to the distinct possibility that genuine long-range antiferromagnetism and superconductivity do not coexist. The data reveal a magnetic quantum critical point where superconductivity first appears, consistent with an exotic quantum phase transition between the two phases [7]. We also demonstrate that the pseudogap phenomenon in the electron-doped materials, which is associated with pronounced charge anomalies [8-11], arises from a build-up of spin correlations, in agreement with recent theoretical proposals [12, 13].