Anisotropic Electronic Correlations in the Spin Density Wave State of La3Ni2O7

The bilayer nickelate superconductor La ₃ Ni ₂ O ₇ undergoes a density wave transition near 150 K that has attracted intensive scrutiny, yet its microscopic origin remains elusive. Here we report polarization-resolved electronic Raman scattering measurements on high-quality single crystals of La ₃ Ni ₂ O ₇ . Below 150 K, we observe a pronounced, symmetry-dependent redistribution of spectral weight in B _1g and B _2g channels, consistent with the formation of spin-density wave (SDW) gaps. Quantitative analysis reveals momentum-selective SDW gap amplitudes, with intermediate-to-strong coupling on the pockets centered at (±π/2,±π/2) and weaker coupling at (±π, 0) and (0,±π), pointing to an unconventional SDW driven by anisotropic electronic correlations. Our results establish the electronic character of the SDW in La ₃ Ni ₂ O ₇ , and provide a microscopic foundation for understanding the emergence of high-temperature superconductivity under pressure in nickelates.