High pressure plays a crucial role in the field of superconductivity. Compressed hydride superconductors are leaders in the race for a material that can conduct electricity without resistance at high or even room temperature. In the present work, we have discovered new lanthanum superhydride, cubic A15-type La$_4$H$_{ 23}$, with lower stabilization pressure compared to the reported $\textit{ fcc}$ LaH$_{ 10}$. Superconducting La$_4$H$_{ 23}$ was obtained by laser heating of LaH$_3$ with ammonia borane at about 120 GPa. Transport measurements reveal the maximum critical temperature $\textit{ T}$$_{ C}$(onset) = 105 K and the critical field $\textit{ H}$$_{ C2}$(0) = 32 T at 118 GPa, as evidenced by the sharp drop of electrical resistance and the displacement of superconducting transitions in applied magnetic fields. Moreover, we provide evidence for unconventional transport associated with a pseudogap phase in La$_4$H$_{ 23}$ using pulsed magnetic fields up to 68 T. A large negative magnetoresistance in the non-superconducting state below 40 K, quasi $\textit{ T}$-linear electrical resistance, and a sign-change of its temperature dependence mark the emergence of pseudogap in this hydride. Discovered lanthanum hydride is a new member of the A15 family of superconductors with $\textit{ T}$$_C$ exceeding the boiling point of liquid nitrogen.
Categories: cond-mat.supr-con cond-mat.mtrl-sci