Large negative magnetoresistance and pseudogap phase in superconducting A15-type La$_4$H$_{23}$

TL;DR

This study reports the discovery of a new lanthanum superhydride, La$_4$H$_{23}$, exhibiting high-temperature superconductivity and pseudogap phenomena under high pressure, with potential implications for room-temperature superconductors.

Contribution

The paper introduces a new A15-type lanthanum hydride with high critical temperature and evidence of pseudogap phase, expanding the understanding of hydride superconductors under high pressure.

Findings

Superconducting transition temperature T$_C$ = 105 K at 118 GPa.

Large negative magnetoresistance observed below 40 K.

Evidence of pseudogap phase with unconventional transport properties.

Abstract

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.