title: Discovery of a superhard iron tetraboride superconductor.
abstract: Single crystals of novel orthorhombic (space group Pnnm) iron tetraboride FeB4 were synthesized at pressures above 8 GPa and high temperatures. Magnetic susceptibility and heat capacity measurements demonstrate bulk superconductivity below 2.9 K. The putative isotope effect on the superconducting critical temperature and the analysis of specific heat data indicate that the superconductivity in FeB4 is likely phonon mediated, which is rare for Fe-based superconductors. The discovered iron tetraboride is highly incompressible and has the nanoindentation hardness of 62(5) GPa; thus, it opens a new class of highly desirable materials combining advanced mechanical properties and superconductivity.
authors.affiliation: Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany and Laboratory of Crystallography, Material Physics and Technology at Extreme Conditions, University of Bayreuth, D-95440 Bayreuth, Germany.
authors.forename: Huiyang
authors.initials: H
authors.lastname: Gou
authors.forename: Natalia
authors.initials: N
authors.lastname: Dubrovinskaia
authors.forename: Elena
authors.initials: E
authors.lastname: Bykova
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Tsirlin
authors.forename: Deepa
authors.initials: D
authors.lastname: Kasinathan
authors.forename: Walter
authors.initials: W
authors.lastname: Schnelle
authors.forename: Asta
authors.initials: A
authors.lastname: Richter
authors.forename: Marco
authors.initials: M
authors.lastname: Merlini
authors.forename: Michael
authors.initials: M
authors.lastname: Hanfland
authors.forename: Artem M
authors.initials: AM
authors.lastname: Abakumov
authors.forename: Dmitry
authors.initials: D
authors.lastname: Batuk
authors.forename: Gustaaf
authors.initials: G
authors.lastname: Van Tendeloo
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Nakajima
authors.forename: Aleksey N
authors.initials: AN
authors.lastname: Kolmogorov
authors.forename: Leonid
authors.initials: L
authors.lastname: Dubrovinsky