Prediction of fully metallic {\sigma}-bonded boron framework induced high superconductivity above 100 K in thermodynamically stable Sr2B5 at 40 GPa

TL;DR

This study predicts a thermodynamically stable Sr2B5 compound under high pressure that exhibits superconductivity above 100 K due to its unique boron framework and strong electron-phonon coupling, potentially operable at ambient conditions.

Contribution

It introduces a new stable boron-based structure with high-temperature superconductivity, expanding the design space for lightweight superconducting materials.

Findings

Sr2B5 is thermodynamically stable at 40 GPa.

Superconducting Tc exceeds 100 K, above liquid nitrogen temperature.

High Tc is due to strong coupling between {\sigma}-bonded bands and phonon modes.

Abstract

Metal borides have been considered as potential high-temperature superconductors since the discovery of record-holding 39 K superconductivity in bulk MgB2. In this work, we identified a superconducting yet thermodynamically stable F43m Sr2B5 at 40 GPa with a unique covalent sp3-hybridized boron framework through extensive first-principles structure searches. Remarkably, solving the anisotropic Migdal-Eliashberg equations resulted in a high superconducting critical temperature (Tc) around 100 K, exceeding the boiling point (77 K) of liquid nitrogen. Our in-depth analysis revealed that the high-temperature superconductivity mainly originates from the strong coupling between the metalized {\sigma}-bonded electronic bands and E phonon modes of boron atoms. Moreover, anharmonic phonon simulations suggest that F43m Sr2B5 might be recovered to ambient pressure. Our current findings provide a prototype structure with a full {\sigma}-bonded boron framework for the design of high-Tc superconducting borides that may expand to a broader variety of lightweight compounds.