Superconductivity with strong electron-phonon coupling in noncentrosymmetric W3Al2C

We report the discovery of superconductivity in ${\mathrm{W}}₃{\mathrm{Al}}₂\mathrm{C}$ (${T}_c=7.6\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) synthesized by high-pressure method. ${\mathrm{W}}₃{\mathrm{Al}}₂\mathrm{C}$ is isostructural to ${\mathrm{Mo}}₃{\mathrm{Al}}₂\mathrm{C}$ (space group $P{4}₁32$) but with stronger spin-orbit coupling (SOC). Different from the ${\mathrm{Mo}}₃{\mathrm{Al}}₂\mathrm{C}$ with metallic nature, the resistivity of the normal state of ${\mathrm{W}}₃{\mathrm{Al}}₂\mathrm{C}$ shows a nonmetallic behavior. A specific-heat jump of $\mathrm{\ensuremath{\Delta}}{C}_es/\ensuremath{\gamma}{T}_c=2.7$ and gap energy of $2\mathrm{\ensuremath{\Delta}}(0)/\ensuremath{\gamma}{T}_c=5.43$ are observed, which are much larger than that of ${\mathrm{Mo}}₃{\mathrm{Al}}₂\mathrm{C}$ (2.1 and 4.03) and the expectation of Bardeen-Cooper-Schrieffer theory (1.43 and 3.52). However, the Sommerfeld coefficient of ${\mathrm{W}}₃{\mathrm{Al}}₂\mathrm{C}$ is less than half of that of its Mo counterpart, and the specific heat above 2 K shows a power-law divergence following ${C}_es/\ensuremath{\gamma}{T}_c\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}\phantom{\rule{4pt}{0ex}}{(T/{T}_c)}^3.3$ rather than an exponential relation. Theoretical calculations show that the Fermi surface of ${\mathrm{W}}₃{\mathrm{Al}}₂\mathrm{C}$ is dominated by W-$5d$ electrons and the inclusion of SOC significantly changes its band structure, density of states, and Fermi surface topology. The realization of superconductivity by replacing $4d$ Mo toward $5d\phantom{\rule{0.16em}{0ex}}\mathrm{W}$ provides a candidate for the search of potential triplet superconductors with enhanced SOC.