Neutron Scattering Study of Spin Density Wave Order in the Superconducting State of Excess-Oxygen-Doped La2CuO4+y

TL;DR

This neutron scattering study reveals that spin density wave order persists within the superconducting state of La2CuO4+y, showing strong correlation between magnetic order and superconductivity, and confirming its robustness near 1/8 doping.

Contribution

First direct observation of incommensurate spin density wave order coexisting with superconductivity in La2CuO4+y, highlighting the persistent antiferromagnetic influence at high doping levels.

Findings

Spin density wave order is incommensurate and long-range in the copper-oxide plane.

Magnetic order appears at the same temperature as superconductivity.

Spin correlations are short-range between planes, similar to the undoped insulator.

Abstract

We report neutron scattering measurements of spin density wave order within the superconducting state of a single crystal of predominately stage-4 La2CuO4+y with a Tc(onset) of 42 K. The low temperature elastic magnetic scattering is incommensurate with the lattice and is characterized by long-range order in the copper-oxide plane with the spin direction identical to that in the insulator. Between neighboring planes, the spins exhibit short-range correlations with a stacking arrangement reminiscent of that in the undoped antiferromagnetic insulator. The elastic magnetic peak intensity appears at the same temperature within the errors as the superconductivity, suggesting that the two phenomena are strongly correlated. These observations directly reveal the persistent influence of the antiferromagnetic order as the doping level increases from the insulator to the superconductor. In addition, our results confirm that spin density wave order for incommensurabilities near 1/8 is a robust feature of the La2CuO4-based superconductors.