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

TL;DR

The study addresses where the SDW gap opens in momentum space for the trilayer nickelate La_4Ni_3O_{10}. It employs polarization-resolved electronic Raman scattering with symmetry decomposition to map momentum-selective gap openings on the α and β Fermi pockets, identifying a gap scale of Δ_{SDW} ≈ 55 meV and a lack of gap along the β diagonal. This gap topology contrasts with the bilayer compound La_3Ni_2O_{7}, where the SDW gap concentrates on the β pocket, suggesting different nesting or scattering vectors (favoring a vector Q_{SDW} linking α and β near X/Y). The results impose new constraints on the microscopic origin of density-wave order and its relation to superconductivity in layered nickelates, highlighting a distinct momentum-space gap topology between bilayer and trilayer members.

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 $α$ pocket at the Brillouin-zone centre and a portion of the $β$ 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 $β$ pockets, implying little or no gap opening. This gap topology contrasts sharply with that in La3Ni2O7, where anisotropic SDW gaps open solely on the $β$ 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.

Figures (3)

• Figure 1: Definition of the Ni–O unit cell, photon polarizations, Fermi pockets, and Raman responses in different polarization configurations. (a) Solid (dashed) lines indicate the 1-Ni (2-Ni) unit cell. The $x$ and $y$ axes are aligned along the Ni–O–Ni bond directions, while the $x'$ and $y'$ polarizations are rotated by 45$^\circ$ clockwise, corresponding to the Ni–Ni directions. (b) Schematic Fermi surface obtained from a tight-binding model with $\alpha$ (red), $\beta_1$ (yellow), $\beta_2$ (green), and $\gamma$ (grey) pockets (see Supplementary Materials F for details). Black arrows denote candidate scattering wave vectors: Q$_1$ and Q$_2$. (c–f) Temperature dependence of the electronic continuum measured in the $xx$, $x'x'$, $xy$, and $x'y'$ channels.
• Figure 2: Electronic continuum spectra in pure symmetries at 50 K and 140 K. Difference spectra [$\chi"$(50 K) - $\chi"$(140 K)] are shown as green curves. Red lines serve as guides to the eye. Insets: Crystal harmonics, proportional to the Raman vertices in the first Brillouin zone, superimposed on the Fermi pockets for the $A_{\rm{1g}}$ , ${B_{\rm{1g}}}$, and ${B_{\rm{2g}}}$ symmetries.
• Figure 3: Comparison of density-wave gaps and candidate scattering vectors in La$_4$Ni$_3$O$_{10}$ and La$_3$Ni$_2$O$_{7}$ . Gapped Fermi pockets are highlighted in (a) $\alpha$ pocket and $\beta$ pocket near XY points of La$_4$Ni$_3$O$_{10}$ and (b) $\beta$ pocket of La$_3$Ni$_2$O$_{7}$ . Black arrows indicate possible scattering wave vectors. '+' and '-' signs denote the parity of the bands determined by the layer index (top and bottom Ni-O planes). The colored shading superimposed on the Fermi surface pockets highlights the momentum regions in which energy gaps open.