W4IrC1−x: a new noncentrosymmetric superconductor with a cubic β-Mn type structure.

We report the discovery of a new noncentrosymmetric superconductor, W₄IrC_1−x, which adopts a cubic β-Mn type structure for x in the range of 0 to 0.2. This compound is stabilized by interstitial carbon and becomes unstable by annealing or varying the W/Ir ratio. We show that both W₄IrC and W₄IrC_0.8 are weakly coupled type-II superconductors with bulk T_c values of 4.77 and 4.87 K, respectively. Remarkably, their zero-temperature upper critical fields reach 8.3–8.8 T, which approach the Pauli paramagnetic limit of ∼9.0 T. Theoretical calculations indicate that the Fermi level of W₄IrC is located at a local maximum of the density of states, which is dominated by the contributions from the W and Ir atoms and significantly enhanced by the spin–orbit coupling. Our study identifies the 5 d element Ir as an optional constituent in forming β-Mn type superconductors. [ABSTRACT FROM AUTHOR]