Stoichiometric Ternary Superhydride ${\mathrm{LaBeH}}_8$ as a New Template for High-Temperature Superconductivity at 110 K under 80 GPa

The search for high-temperature superconducting superhydrides has recently moved into a new phase by going beyond extensively probed binary compounds and focusing on ternary ones with vastly expanded material types and configurations for property optimization. Theoretical and experimental works have revealed promising ternary compounds that superconduct at or above room temperature, but it remains a pressing challenge to synthesize stoichiometric ternary compounds with a well-resolved crystal structure that can host high-temperature superconductivity at submegabar pressures. Here, we report on the successful synthesis of ternary ${\mathrm{LaBeH}}_8$ obtained via compression in a diamond anvil cell under 110–130 GPa. X-ray diffraction unveils a rocksalt-like structure composing La and ${\mathrm{BeH}}_8$ units in the lattice. Transport measurements determined superconductivity with critical temperature $T_c$ up to 110 K at 80 GPa, as evidenced by a sharp drop of resistivity to zero and a characteristic shift of $T_c$ driven by a magnetic field. Our experiment establishes the first superconductive ternary compound with a resolved crystal structure. These findings raise the prospects of rational development of the class of high-$T_c$ superhydrides among ternary compounds, opening greatly expanded and more diverse structural space for exploration and discovery of superhydrides with enhanced high-$T_c$ superconductivity.

Figure 1

(a) Synchrotron x-ray diffraction pattern of the heated sample (cell 12) at 120 GPa and the Rietveld refinement of the $Fm$-$3m$ ${\mathrm{LaBeH}}_8$ structure. The high-intensity points caused by single-crystal-like diffraction are masked, and the continuous background is removed before performing the integration and Rietveld analysis. The black circles and red and blue curves correspond to the experimental data, Rietveld refinement fit, and residue, respectively. The red ticks indicate the calculated peak positions for $Fm$-$3m$ ${\mathrm{LaBeH}}_8$. The crystal surface indexes are marked next to the peaks. The cake plot shows some textures that can be fitted by spherical harmonics, where the harmonic order is 10 and the texture index is 1.386. (b) Experimental equation-of-state data (circle symbols) for the synthetic samples are compared with the theoretical data (dashed line) derived from the $Fm$-$3m$ structured ${\mathrm{LaBeH}}_8$. The experimental data from cell 10 and cell 12 are marked with red and blue circles, respectively. Inset figure depicts the superconducting transition with $T_c\sim 90\mathrm{K}$ in the electrical measurement for cell 10 at 120 GPa and the crystal structure of ${\mathrm{LaBeH}}_8$.

Figure 2

(a) The observation of superconductivity in ${\mathrm{LaBeH}}_8$ (cell 1). The vertical axis is the resistance divided by the resistance at 110 K. The resistance data with near zero values are shown on a smaller scale in the left inset. (b) The dependence of the onset of superconducting temperature $T_c$ data on pressure for 11 different experimental runs from cells 1–11 (Figs. S4–S15 [38]). The experimental data are marked in different colors. The open and solid symbols represent the data obtained from compression and decompression, respectively.

Figure 3

(a) Temperature dependence of the electrical resistance in cell 3 under applied magnetic fields of $\mathrm{H}=0$, 1, 3, 5, 7, and 9 T at 120 GPa. (b) Upper critical field $H_{c2}$ versus temperature following the criteria of 90% of the resistance in the metallic state at 120 GPa, fitted with the GL and WHH models. Inset: the dependence of the $T_c$ under the applied magnetic field.