Single crystals of novel orthorhombic (space group Pnnm) iron tetraboride FeB4 were synthesised at pressures above 8 GPa and high temperatures. Magnetic susceptibility measurements demonstrated bulk superconductivity below 2.9 K. The putative isotope effect on the superconducting critical temperature indicates that FeB4 is likely a phonon-mediated superconductor, which is unexpected in the light of previous knowledge on Fe-based superconductors. The discovered iron tetraboride is highly incompressible and has the nanoindentation hardness of 65(5) GPa, thus, it opens a new class of highly desirable materials combining advanced mechanical properties and superconductivity.
@article{arxiv.1304.5106,
title = {Discovery of a superhard iron tetraboride superconductor},
author = {Huiyang Gou and Natalia Dubrovinskaia and Elena Bykova and Alexander A. Tsirlin and Deepa Kasinathan and Asta Richter and Marco Merlini and Michael Hanfland and Artem M. Abakumov and Dmitry Batuk and Gustaaf Van Tendeloo and Yoichi Nakajima and Aleksey N. Kolmogorov and Leonid Dubrovinsky},
journal= {arXiv preprint arXiv:1304.5106},
year = {2015}
}