High-temperature multigap superconductivity in two-dimensional metal-borides

Abstract

Using first-principles calculations in combination with the Eliashberg formalism, we systematically investigated phonon-mediated superconductivity in two-dimensional (2D) metal-boride crystals, consisting of a boron honeycomb network doped by diverse metal elements. Such 2D metal-boride compounds, named MBenes, are chemically exfoliable from single-crystalline layered ternary borides (MAB phases). First we identified the MBene layers with potential for superconductivity via isotropic Eliashberg calculations, considering a wide range of metal elements, with focus on alkaline earth and transition metals. Subsequently, we performed a detailed analysis of the prominent superconducting MBenes by solving the anisotropic Eliashberg equations. The obtained high critical temperatures (up to 72 K), as well as the rich multigap superconducting behavior, recommend these crystals for further use in multifunctional 2D heterostructures and superconducting device applications. I. INTRODUCTIONThe potential of two-dimensional (2D) materials in terms of future technological applications is well established [1-3], as demonstrated for example through both theoretical and experimental studies with regard to transistors [4, 5], energy harvesters [6-9], and sensors [10-12]. Recently, with the successful fabrication of 2D metallic materials such as In [13], Pb [14], NbSe 2 [15, 16], FeSe [17], MgB 2 [18], Mo 2 C [19], Nb 2 C [20], doped graphene [21-23],and twisted bilayer graphene [24], superconductivity has been added to the range of properties yielding possible applications. However, taking advantage of that potential requires a detailed investigation and understanding of the origins and behavior of the superconductivity in these two-dimensional systems, to ensure reproducibly robust superconducting behavior up to sufficiently high temperatures.One of the well-known material families to examine the behavior of superconductivity at the 3D-to-2D transition are the layered hexagonal metal borides (MB 2 ) with P6/mmm space group symmetry. Among them, bulk MgB 2 has been extensively studied over the past two decades, and is still the electron-phonon (e-ph) mediated superconductor with highest