Contrasting Momentum-Selective Spin-Density-Wave Gaps in Bilayer and Trilayer Nickelates

TL;DR

This study uses polarization-resolved Raman scattering to map the momentum-dependent spin-density-wave gaps in bilayer and trilayer nickelates, revealing distinct gap topologies that inform the understanding of their density-wave instabilities and potential link to superconductivity.

Contribution

It provides the first detailed momentum-space mapping of SDW gaps in trilayer nickelates, contrasting with bilayer counterparts, and constrains theories of their density-wave mechanisms.

Findings

SDW gap affects both the $ ext{ extalpha}$ and part of the $ ext{ extbeta}$ pockets in trilayer nickelates.

No gap opening observed along the diagonal of $ ext{ extbeta}$ pockets in trilayer nickelates.

Distinct gap topology between bilayer and trilayer nickelates constrains the density-wave instability mechanisms.

Abstract

Resolving where the density-wave gap opens in momentum space is essential for identifying the microscopic origin of the instability in layered nickelates. Using polarization-resolved electronic Raman scattering, we map the momentum selectivity of the spin-density-wave (SDW) gap in trilayer La4Ni3O10. We observe a SDW-induced redistribution of spectral weight on both the $\alpha$ pocket at the Brillouin-zone centre and a portion of the $\beta$ pocket near the zone boundary, characterized by gap energies of approximately 55~meV. In contrast, no comparable spectral weight suppression is observed along the diagonal region of $\beta$ pockets, implying little or no gap opening. This gap topology contrasts sharply with that in La3Ni2O7, where anisotropic SDW gaps open solely on the $\beta$ pocket. Our results establish a distinct momentum-space gap topology between bilayer and trilayer nickelates, placing new constraints on the ordering wave vector and the mechanism of the density-wave instability relevant to superconductivity.