Speaker
Description
Ruddlesden-Popper (RP) nickelates exhibit high-temperature superconductivity closely intertwined with charge and spin density-wave order. However, fundamental questions remain regarding the orbital character, symmetry, and gap formation associated with these density-wave instabilities. Using polarization-resolved Raman scattering on the trilayer compound La$_4$Ni$_3$O$_{10}$, we resolve characteristic phonon anomalies and a redistribution of electronic spectral weight across the density-wave transitions. Momentum-selective electronic Raman responses, combined with multiorbital model calculations, reveal a density-wave-induced gap with incoherent, non-mean-field-like opening and involvement from both Ni $d_{x^2-y^2}$ and $d_{z^2}$ states [1]. These results help reconcile conflicting experimental reports on the density-wave gap and underscore its multiorbital character. In addition, I will discuss complementary Raman investigations of the monolayer-trilayer polymorph La$_3$Ni$_2$O$_7$, providing a broader perspective on how structural complexity within the RP series influences lattice dynamics and intertwined electronic instabilities [2].
[1] A. Suthar et al., arXiv:2508.06440
[2] V. Sundaramurthy et al., arXiv:2512.17583v1