Kagome van-der-Waals Pd3P2S8 with flat band

Crystal structure, properties and pressure-induced insulator-metal transition in layered kagome chalcogenides

Layered materials with kagome lattice have attracted a lot of attention due to the presence of nontrivial topological bands and correlated electronic states with tunability. In this work, we investigate a unique van der Waals (vdW) material system,A2M3X4(A= K, Rb, Cs;M= Ni, Pd;X= S, Se), where transition metal kagome lattices, chalcogen honeycomb lattices and alkali metal triangular lattices coexist simultaneously. A notable feature of this material is that each Ni/Pd atom is positioned in the center of four chalcogen atoms, forming a local square-planar environment. This crystal field environment results in a low spin stateS= 0 of Ni2+/Pd2+. A systematic study of the crystal growth, crystal structure, magnetic and transport properties of two representative compounds, Rb2Ni3S4and Cs2Ni3Se4, has been carried out on powder and single crystal samples. Both compounds exhibit nonmagneticp-type semiconducting behavior, closely related to the particular chemical environment of Ni2+ions and the alkali metal intercalated vdW structure. Additionally, Cs2Ni3Se4undergoes an insulator-metal transition (IMT) in transport measurements under pressure up to 87.1 GPa without any structural phase transition, while Rb2Ni3S4shows the tendency to be metalized.

Superconductivity and phase transitions in Kagome compound Pd3P2S8from first-principles calculation

Pd3P2S8is a semiconductor that contains Kagome lattices, which exhibits various physical phenomena. Structural searches of Pd3P2S8in the pressure range from 0 to 120 GPa have revealed two phases of the space groupP3‾m1(designated asP3‾m1-1 andP3‾m1-2) and two phases of the space groupC2/m(designated asC2/m-1 andC2/m-2), with all butC2/m-2 phase being dynamically stable. Electron-phonon calculations combined with Bardeen-Cooper-Schrieffer's argument have shown that both phases are superconductors. Notably, theP3‾m1-1 phase undergoes a semiconductor-to-superconductor transition, with superconducting critical temperature (Tc) increasing up to a maximum of 9.13 K at 70 GPa. BothC2/m-1 andP3‾m1-2 phases exhibit superconductivity at 0 GPa. Our calculations demonstrate several new superconducting phases of Pd3P2S8, providing a pathway and platform for exploring superconductivity in materials with Kagome lattices and expanding the options for studying such lattices.

Epitaxial Growth of Single-Layer Kagome Nanoflakes with Topological Band Inversion

The kagome lattice has attracted intense interest with the promise of realizing topological phases built from strongly interacting electrons. However, fabricating two-dimensional (2D) kagome materials with nontrivial topology is still a key challenge. Here, we report the growth of single-layer iron germanide kagome nanoflakes by molecular beam epitaxy. Using scanning tunneling microscopy/spectroscopy, we unravel the real-space electronic localization of the kagome flat bands. First-principles calculations demonstrate the topological band inversion, suggesting the topological nature of the experimentally observed edge mode. Apart from the intrinsic topological states that potentially host chiral edge modes, the realization of kagome materials in the 2D limit also holds promise for future studies of geometric frustration.

Simple Chemical Rules for Predicting Band Structures of Kagome Materials

Compounds featuring a kagome lattice are studied for a wide range of properties, from localized magnetism to massless and massive Dirac Fermions. These properties come from the symmetry of the kagome lattice, which gives rise to Dirac cones and flat bands. However, not all compounds with a kagome sublattice show properties related to it. We derive chemical rules predicting if the low-energy physics of a material is determined by the kagome sublattice and bands arising from it. After sorting out all known crystals with the kagome lattice into four groups, we use chemical heuristics and local symmetry to explain additional conditions that need to be met to have kagome bands near the Fermi level.

Realizing Kagome Band Structure in Two-Dimensional Kagome Surface States of RV_{6}Sn_{6} (R=Gd, Ho)

We report angle resolved photoemission experiments on a newly discovered family of kagome metals RV_{6}Sn_{6} (R=Gd, Ho). Intrinsic bulk states and surface states of the vanadium kagome layer are differentiated from those of other atomic sublattices by the real-space resolution of the measurements with a small beam spot. Characteristic Dirac cone, saddle point, and flat bands of the kagome lattice are observed. Our results establish the two-dimensional (2D) kagome surface states as a new platform to investigate the intrinsic kagome physics.