Two distinct charge density waves in the quasi-one-dimensional metal Sr0.95NbO3.37 revealed by resonant soft X-ray scattering

The interplay of electron-electron and electron-lattice interactions plays an important role in determining exotic properties in strongly correlated electron systems. Of particular interest is quasi-one-dimensional SrNbOx metals, which are perovskite-related layered Carpy-Galy phases. Quasi-one-dimensional metals often exhibit a charge density wave (CDW) accompanied by lattice distortion; however, to date, the presence of a CDW in a quasi-one-dimensional metallic Carpy-Galy phase has not been detected. Here, we report the discovery of two distinct and simultaneous commensurate CDWs in Sr0.95NbO3.37 using resonant soft X-ray scattering (RSXS), namely, an electronic-(001) superlattice below ~ 200 K and an electronic-(002) Bragg peak. We also observe a non-electronic-(002) Bragg peak showing lattice distortion below ~ 150 K. Through the temperature dependence and resonance profile of these CDWs and the lattice distortion, as well as the relationship between the wavelength and charge density, these CDWs are determined to be Wigner crystals and Peierls-like instabilities, respectively. The electron‒electron interaction is strong and dominant even up to 350 K, and upon cooling, it drives the electron–lattice interaction. The correlation length of the electronic-(001) superlattice is surprisingly larger than that of the electronic-(002) Bragg peak, and the superlattice is highly anisotropic. Supported by theoretical calculations, the CDWs are determined by the charge anisotropy and redistribution between the O-2p and Nb-4d orbitals, and the strength of the electronic-(001) superlattice is within the strong coupling limit. Understanding how electrons interact in materials is vital for fundamental research and creating new technologies. However, the connection between different CDWs and their impact on materials, particularly inorganic systems, is unclear. The study, led by Andrivo Rusydi, aimed to understand CDWs in a specific crystal type, a quasi-one-dimensional metal. Rusydi and his team used resonant soft X-ray scattering to identify two distinct CDWs in one crystal. Their results showed that the Wigner crystal appeared without any crystal structure changes, while the Peierls-like instability was associated with a crystal distortion. These findings suggest that strong electron-electron interactions can drive changes in the crystal lattice, leading to different CDWs. This research offers new insights into the complex relationship between electron interactions and CDWs in inorganic materials. The advancements made in this study could impact future electronic devices development and understanding superconductivity. This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author. The interplay of electron-electron and electron-lattice interactions plays an important role in determining exotic properties in strongly correlated electron systems. Here, we report the discovery of two distinct and simultaneous commensurate CDWs, Wigner crystal and Peierls-like instabilities, in Sr0.95NbO3.37 using resonant soft X-ray scattering. These CDWs arise from charge anisotropy and redistribution in Nb 4d – O 2p hybridization and influence transport and optical gaps. The strength of Wigner crystal is within the strong coupling limit. This study paves the way for utilizing RSXS to distinguish CDWs and calls for further investigation of electron‒electron and electron–lattice interactions in inorganic systems