Hidden itinerant-spin phase in heavily-overdoped La2-xSrxCuO4 revealed by dilute Fe doping: A combined neutron scattering and angle-resolved photoemission study

TL;DR

This study reveals a hidden itinerant-spin density wave in heavily-overdoped La2-xSrxCuO4 induced by minimal Fe doping, using neutron scattering and ARPES to connect Fermi surface nesting with magnetic order.

Contribution

It demonstrates a novel method to detect hidden SDW propensity in non-magnetic metals and identifies the itinerant nature of spins in heavily-overdoped cuprates.

Findings

Fe doping induces incommensurate magnetic order below 20 K.

Fermi surface nesting drives the magnetic order.

First example of itinerant-spin density wave in cuprates.

Abstract

We demonstrated experimentally a direct way to probe a hidden propensity to the formation of spin density wave (SDW) in a non-magnetic metal with strong Fermi surface nesting. Substituting Fe for a tiny amount of Cu (1%) induced an incommensurate magnetic order below 20 K in heavily-overdoped La2-xSrxCuO4 (LSCO). Elastic neutron scattering suggested that this order cannot be ascribed to the localized spins on Cu or doped Fe. Angle-resolved photoemission spectroscopy (ARPES), combined with numerical calculations, revealed a strong Fermi surface nesting inherent in the pristine LSCO that likely drives this order. The heavily-overdoped Fe-doped LSCO thus represents the first plausible example of the long-sought "itinerant-spin extreme" of cuprates, where the spins of itinerant doped holes define the magnetic ordering ground state. This finding complements the current picture of cuprate spin physics that highlights the predominant role of localized spins at lower dopings. The demonstrated set of methods could potentially apply to studying hidden density-wave instabilities of other "nested" materials on the verge of density wave ordering.