Two-dimensional potassium borides with hidden kagome-like lattice: Topological semimetals, van Hove singularities, and superconductivity

The coexistence of nontrivial topological properties and superconductivity in a material offers the potential to achieve topological superconductivity and Majorana zero modes. However, research on ideal topological semimetals with superconductivity has been limited. In this paper, we utilize first-principles calculations to predict the existence of three two-dimensional potassium borides (K2B9, KB9, and KB18) with a hidden kagome-like lattice structure, inspired by the arrangement of the K2B9- cluster in an inverse sandwich configuration. Our findings reveal that all three materials exhibit phonon-mediated superconductivity, with transition temperatures (T-c) of 12.56, 14.46, and 10.50 K, respectively. Furthermore, K2B9 and KB18 are identified as topological nodalline semimetals, while KB9 demonstrates the characteristics of an ideal Dirac semimetal due to the broken sigma(h) mirror symmetry and appropriate potassium content. The topological properties arise from the band inversion of the boron atom's p(x) + p(y) and p(z) orbitals within the B-9 layer. Intriguingly, KB9 exhibits coexisting Dirac points and van Hove singularities near the Fermi level, which are a consequence of the hidden kagome-like lattice, thereby enhancing the superconducting transition temperature (T-c). This research not only sheds light on the pivotal role played by the orbital character of the B-9 layer in the kagome-like lattice of potassium borides but also presents a strategy for achieving the coexistence of topological properties and superconductivity, thereby opening up possibilities for the realization of exotic physics.

Automated summary

This study utilizes first-principles calculations to discover three two-dimensional potassium borides with a hidden kagome-like lattice structure, and demonstrates their topological semimetal characteristics and phonon-mediated superconductivity.