D-Wave Superconducting Gap Symmetry as a Model for Nb1−xMoxB2 (x = 0.25; 1.0) and WB2 Diborides

Recently, Pei et al. (arXiv2105.13250) reported that ambient pressure ${\beta}$-MoB$_2$ exhibits a phase transition to ${\alpha}$-MoB$_2$ (space group: $P6/mmm$) at P~70 GPa and this high-pressure is high-temperature superconductor exhibited $T_c=32 K$ P~110 GPa. Despite has the same crystalline structure as MgB$_2$2 $T_c$'s of MgB$_2$ are very close, first principles calculations showed in states near Fermi level, ${\epsilon}_F$, dominated by $d$-electrons Mo atoms, while $p$-orbitals boron atomic sheets dominantly contribute ${\epsilon}_F$. More recently, Hire (arXiv2212.14869) $P6/mmm$-phase can be stabilized $Nb_{1-x}Mo_{x}B_{2}$ solid solutions, these ternary alloys exhibit $T_c=8 K$. In addition, (Sci. China-Phys. Mech. Astron. 65, 287412 (2022)) compressed WB$_2$ $T_c=15 P~121 Here, we analyzed experimental data for $P6/mmm$-phases (x = 0.25; 1.0) highly-compressed WB$_2$, three phases $d$-wave superconductivity. We also deduced gap-to-transition temperature ratio phases. found $Nb_{0.75}Mo_{0.25}B_{2}$ high strength nonadiabaticity, which quantified $T_{\theta}/T_F=3.5$, one order magnitude exceeds MgB$_2$, ${\alpha}$-MoB$_2$, pnictides, cuprates, hydrides.