Emergent Kagome Electrides

In a two-dimensional (2D) Kagome lattice, the ideal Kagome bands including Dirac cones, van Hove singularities, and a flat band are highly expected, because they can provide a promising platform to investigate novel physical phenomena. However, in the reported Kagome materials, the complex 3D and multiorder electron hoppings result in the disappearance of the ideal Kagome bands in these systems. Here, we propose an alternative way to achieve the ideal Kagome bands in non-Kagome materials by confining excess electrons in the system to the crystal interstitial sites to form a 2D Kagome lattice, coined as a Kagome electride. Then, we predict two novel stable 2D Kagome electrides in hexagonal materials Li5Si and Li5Sn, whose band structures are similar to the ideal Kagome bands, including topological Dirac cones with beautiful Fermi arcs in their surface states, van Hove singularities, and a flat band. In addition, Li5Si is revealed to be a low-temperature superconductor at ambient pressure, and its superconducting transition temperature T-c can be increased from 1.1 K at 0 GPa to 7.2 K at 100 GPa. The high T-c is unveiled to be the consequence of strong electron-phonon coupling originated from the sp-hybridized phonon-coupled bands and phonon softening caused by strong Fermi nesting. Due to the strong Fermi nesting, the charge density wave phase transition occurs at 110 GPa with the lattice reconstructed from hexagonal to orthorhombic, accompanied with the increase of T-c to 10.5 K. Our findings pave an alternative way to fabricate more real materials with Kagome bands in electrides.

Automated summary

A method to achieve ideal Kagome bands in non-Kagome materials has been proposed by confining excess electrons in the crystal interstitial sites to form a 2D Kagome lattice. Two novel stable 2D Kagome electrides in hexagonal materials Li5Si and Li5Sn have been predicted, with band structures similar to ideal Kagome bands and featuring topological Dirac cones, van Hove singularities, and a flat band. Additionally, Li5Si has been found to be a low-temperature superconductor at ambient pressure.