Non-Fermi-Liquid Behavior of Superconducting SnH₄

The chemical interaction of Sn with H₂ by X-ray diffraction methods at pressures of 180-210 GPa is studied. A previously unknown tetrahydride SnH₄ with a cubic structure (fcc) exhibiting superconducting properties below T_C  = 72 K is obtained; the formation of a high molecular C2/m-SnH₁₄ superhydride and several lower hydrides, fcc SnH₂ , and C2-Sn₁₂ H₁₈ , is also detected. The temperature dependence of critical current density J_C (T) in SnH₄ yields the superconducting gap 2Δ(0) = 21.6 meV at 180 GPa. SnH₄ has unusual behavior in strong magnetic fields: B,T-linear dependences of magnetoresistance and the upper critical magnetic field B_C2 (T) ∝ (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 SnH₄ 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.