Nature of magnetism in bilayer nickelate La3Ni2O7 single crystals

TL;DR

This study uses neutron scattering to elucidate the magnetic properties of La3Ni2O7, revealing complex spin dynamics and interactions that differ from cuprates, and their potential relevance to high-temperature superconductivity.

Contribution

First direct measurement of spin order and excitations in La3Ni2O7, revealing a bilayer Heisenberg model with strong interlayer exchange and stripe-type magnetic order.

Findings

Observed well-defined spin excitations with a 5 meV gap.

Identified antiferromagnetic interlayer coupling and competing in-plane interactions.

Found enhanced local dynamic susceptibility despite lower spin-wave bandwidth.

Abstract

The recent discovery of high-temperature superconductivity in pressurized and thin film nickelates has generated intense interest, yet the nature of magnetism in their ambient-pressure parent phases remains poorly understood, despite its potentially crucial role in pairing. Here we use neutron scattering to resolve the spin order and dynamics of single-crystalline La3Ni2O7, an ambient-pressure parent of this class. Well defined spin excitations are observed at Q = (0, 0.5, 2.5), featuring a~5 meV spin gap and anisotropic in-plane dispersions, with zone-boundary softening along the transverse direction indicative of competing exchange interactions. The excitations exhibit pronounced out-of-plane modulations with bilayer periodicity, providing direct evidence for antiferromagnetic interlayer coupling. Their dispersion is well described by a bilayer Heisenberg Hamiltonian with strong interlayer exchange and competing in-plane couplings within a stripe-type magnetic order. Normalization of the spectra to absolute units reveals that, although the spin-wave bandwidth is only about 25% of that in cuprates, the local dynamic susceptibility at comparable energies is significantly enhanced, yielding a total fluctuating moment of comparable magnitude. These results highlight intense mid-energy spin excitations rooted in substantial electronic correlations as a defining feature of this family, establishing a magnetic framework distinct from cuprates and directly relevant to understanding superconductivity in this system.