Observation of the unusual metallic state in hydride superconductor A15-La4H23

The discovery of high-temperature superconductivity in hydrogen-rich compounds such as H₃S and LaH₁₀ has rekindled researchers' fervent quest for room-temperature superconductors. The pulsed magnetic fields will bring some difficulties like narrow magnetic apertures and magnetically-induced currents. Therefore, the experimental investigations on the transport properties of hydride superconductors are constrained within a limited range of magnetic fields, when conducting measurements under extremely high pressures and strong magnetic fields. Utilizing various extreme conditions including high pressure, high temperature, and strong magnetic fields contribute to the exploration of the new phenomena and novel insights in the field of hydride superconductors.

Recently, Professor Xiaoli Huang from Jilin University, Dr. Dmitrii Semenok from Center for High Pressure Science and Technology Advanced Research, and Professor Tian Cui from Ningbo University et al., successfully synthesized a novel hydride superconductor, A15-La₄H₂₃ through the high-temperature and high-pressure techniques. Under strong pulsed magnetic field conditions, an unusual metallic state in A15-La₄H₂₃ was observed. This work elucidates the anomalous electronic structure properties of A15-type La₄H₂₃ under strong magnetic field conditions, advancing our understanding of quantum transport behaviors in hydride superconductors. This work titled "Unusual metallic state in superconducting A15-type La₄H₂₃," has been published in National Science Review (2024 Issue 12).

The research team successfully obtained a novel hydride superconductor under high-temperature and high-pressure conditions. The in-situ high-pressure electrical transport experiments revealed that the maximum superconducting critical temperature of 105 K with the pressure of 118 GPa, and this phase remained stable up to 91 GPa. The shift of the transition temperature towards lower temperatures with the increasing applied magnetic fields further confirmed the presence of the superconductivity. The fitting of the upper critical fields using the WHH and GL models yielded values of 33 T and 24 T at 114 GPa, respectively. High-pressure in-situ synchrotron XRD measurements confirmed the crystal structure of the superconducting phase as Pm3¯n-La₄H₂₃. This superconducting phase possesses a typical A15-type structure, similar to the known A₃B-type superconductors such as V₃Si (T_c=17 K), Nb₃Ge (T_c=23.2 K), and Nb₃Sn (T_c=18.3 K). The cubic-phase La₄H₂₃ exhibits the highest superconducting critical temperature among A15-type structured compounds. Under the strong pulsed magnetic fields up to 68 T, the La₄H₂₃ sample displayed significant negative magnetoresistance below 40 K, confirming the presence of an unusual metallic state. This work expands our understanding of the transport behavior in hydride superconductors and suggests new directions and insights for future research in hydride superconductors.

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