Single crystal growth, structural and physical properties, and absence of a charge density wave in Ti ₀.₈₅ Fe₆ Ge₆

Kagome materials with charge density waves (CDWs) are fascinating quantum systems, offering an ideal platform to explore intertwined orders and to uncover novel mechanisms behind CDW formation. Chemical models have been developed and applied to predict CDW in 𝐴⁢𝑀$_6$⁢𝑋$_6$-type kagome materials, such as the rattling chain model based on ScV$_6$⁢Sn$_6$ and the magnetic energy-saving model based on FeGe. In this study, we successfully synthesized Ti$_{0.85}$⁢Fe$_6$⁢Ge$_6$ single crystals using the vapor transport method. As predicted by the rattling chain model, these crystals are expected to exhibit kagome CDW behavior. Magnetization measurements indicate that Ti$_{0.85}$⁢Fe$_6$⁢Ge$_6$ is an easy-axis antiferromagnet with 𝑇$_N$= 488 K, and transport measurements reveal metallic behavior primarily driven by electron-type carriers. However, no clear signatures of a CDW were observed in Ti$_{0.85}$⁢Fe$_6$⁢Ge$_6$. Density functional theory calculations demonstrate a markedly distinct electronic structure compared to related compounds: instead of a carrier-doping-induced rigid shift, the density of states shifted away from the Fermi level. ... mehrConsistent with our structural investigations, the absence of a CDW and the unusual band structure can be attributed to the bonding characteristic within Ti$_{0.85}$⁢Fe$_6$⁢Ge$_6$. The strong covalent bonds of Ti-Ge1b, along with the solid Ge1b-Ge1b dimers, prevent the Ti-Ge1b-Ge1b-Ti chain from rattling. The presence of an Fe-Fe antibonding state at the Fermi level enhances the spin polarization and depletes the electronic density around the Fermi level. Our results suggest that both the ionic radius and the bonding characteristics of the filler atom are crucial for the formation of CDWs in kagome materials. These factors can serve as supplementary terms to the rattling chain model, providing new insights for the discovery of novel kagome CDW materials.