Oxygen-isotope effect on density wave transitions in La${}_3$Ni${}_2$O${}_7$

Abstract

TThe isotope effect is a powerful probe of electron-phonon interactions in solid-state systems, offering key insights into how atomic mass influences emergent quantum states. Here, the impact of oxygen isotope substitution (${}^{16}\mathrm{O}\to {}^{18}\mathrm{O}$) on charge- and spin-density wave (CDW and SDW) transitions in the double-layer Ruddlesden-Popper nickelate La${}_3$Ni${}_2$O${}_7$ is investigated. A clear isotope effect is observed in the CDW transition: the transition temperature ($T_{\mathrm{CDW}}$) increases upon ${}^{18}$O substitution. In contrast, the SDW transition temperature remains unaffected within experimental uncertainty. These findings point to a strong involvement of lattice vibrations in the formation of charge order, while spin order appears to be predominantly of electronic origin. The results suggest that electron-phonon coupling, manifested through the CDW response to isotope substitution, may be relevant to the superconducting pairing mechanism in Ruddlesden-Popper nickelates.

10 pages, 3 figures