Design principle for high-temperature superconductivity in ternary borides at ambient pressure

Abstract

The discovery of metal borides with higher transition temperature (Tc) has been receiving continuous attention since the observation of superconductivity in MgB2 at 39 K. Here we propose a rational design strategy for high-Tc ternary metal borides through the cosubstitution of Mg with two compensating metal elements that possess an effective isovalency of 2. Guided by this principle, we theoretically predict a collection of ternary boride superconductors, including a representative example of KAlB4 that has an isostructure to MgB2, with Tc up to 67 K at ambient pressure. Our detailed analysis reveals that, compared with MgB2, due to the Stark effect caused by the difference in valence of two metal ions, the σ bands of B layers get significant splitting and exhibit more flat character, resulting in enhanced electronic occupation; furthermore, the softened in-plane E2g modes produce larger deformation potential and electron-phonon coupling with B σ states, which in turn results in larger superconducting gaps and much higher Tc value in KAlB4. We further propose a feasible synthesis route of KAlB4 to stimulate experimental progress. Our approach paves the way for finding more high-Tc ternary boride superconductors at ambient pressure.

Source-reported materials — not catalogue approval

Similar papers