Non-Fermi-Liquid Behavior of Superconducting SnH${}_4$

We studied chemical interaction of Sn with H${}_2$ by X-ray diffraction methods at pressures of 180-210 GPa. A previously unknown tetrahydride SnH${}_4$ with a cubic structure ($fcc$) exhibiting superconducting properties below $T$${}_C$ = 72 K was obtained; the formation of a high molecular $C2\mathrm{/}m$-SnH${}_{14}$ superhydride and several lower hydrides, $fcc$ SnH${}_2$ and $C2$-Sn${}_{12}$H${}_{18}$, was also detected. The temperature dependence of critical current density $J$${}_C$(T) in SnH${}_4$ yields the superconducting gap 2$\mathrm{\Delta }$(0) = 23 meV at 180 GPa. SnH${}_4$ has unusual behavior in strong magnetic fields: $B,T$-linear dependences of magnetoresistance and the upper critical magnetic field $B$${}_{C2}$(T) $\propto$ ($T$${}_C$ - $T$). The latter contradicts the Wertheimer-Helfand-Hohenberg model developed for conventional superconductors. Along with this, the temperature dependence of electrical resistance of $fcc$ SnH${}_4$ in non-superconducting state exhibits a deviation from what is expected for phonon-mediated scattering described by the Bloch-Grüneisen model, and is beyond the framework of the Fermi liquid theory. Such anomalies occur for many superhydrides, making them much closer to cuprates than previously believed.