Diboride compounds doped with transition metals$\unicode{x2013}$a route to superconductivity through structure stabilization as well as defects

Abstract

Recent investigations into MoB${}_2$ have unveiled a direct connection between a pressure-induced structural transition to a P6/mmm space group structure and the emergence of superconductivity, producing critical temperatures up to 32 K at 100 GPa. This pressure-induced superconducting state underscores the potential of doped MoB${}_2$ as a possible candidate for metastable superconductivity at ambient pressure. In this work, we demonstrate that doping by Zr, Hf, or Ta stabilizes the P6/mmm structure at ambient pressure and results in the realization of a superconducting state with critical temperatures ranging from 2.4 up to 8.5 K depending on the specific doping. We estimate the electron-phonon coupling $\lambda$ and the density of states based on resistivity and specific heat data, finding that $\lambda$ ranges from 0.4 - 0.6 for these compounds. Finally, to investigate the role of possible metastable defect structures on the critical temperature, we analyze MoB${}_2$, MoB${}_{2.5}$, and Nb/Zr-doped MoB${}_2$ using rapid cooling techniques. Notably, splat-quenching produces samples with higher critical temperatures and even retains superconductivity in MoB${}_2$ at ambient pressure, achieving a critical temperature of 4.5 K.

11 pages, 10 figures (Updated version Oct. 11 2023 ==> arXiv title fixed)

References in corpus (4)

• Review of Transition-Metal Diboride Thin Films
• Phononic Helical Nodal Lines with $\mathcal{P}\mathcal{T}$ Protection in MoB${}_2$
• High critical field superconductivity at ambient pressure in MoB${}_2$ stabilized in the P6/mmm structure via Nb substitution
• Nb-substitution suppresses the superconducting critical temperature of pressurized MoB${}_2$

Cited by in corpus (2)

• Accelerating superconductor discovery through tempered deep learning of the electron-phonon spectral function
• Superconductivity in WBe2