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‐Sn₁₂H₁₈, 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.