Résumé :

The search for room temperature superconductivity has accelerated dramatically in the last few years driven largely by theoretical predictions that first indicated alloying dense hy drogen with other elements could produce conventional phonon-mediated superconductivity at very high temperatures and at accessible pressures, and more recently, with the success of structure search methods that have identified specific candidates and pressure-temperature (P-T) conditions for synthesis. These theoretical advances have prompted improvements in experimental techniques to test these predictions. As a result, experimental studies of simple binary hydrides under pressure have yielded high critical superconducting transition temperatures (Tc), of 260 K in LaH10, close to the commonly accepted threshold for room temperature, 293 K, at pressures near 180 GPa. We successfully synthesized a metallic La based superhydride from La metal and ammonia borane, NH3BH3, and find an initial multi-step transition with a Tc of 294 K for the highest onset, in line with previously reported work [1],[2]. When subjected to subsequent thermal excursions to higher temperatures that promoted a chemical reaction to a ternary or higher order system, the transition temperature was driven to higher temperatures. X-Ray structural data confirm the formation of a higher order hydride. Although the reaction does not appear to be complete, the onset temperature was pushed from 294 K to 556 K. The results provide evidence for hot superconductivity well above room temperature, in line with recent predictions for a higher order hydride under pressure [3].

[1] Somayazulu, M. et al. Evidence for Superconductivity above 260 K in Lanthanum Superhydride at Megabar Pressures. Physical Review Letters 122 (2019).

[2] Drozdov, A. P. et al. Superconductivity at 250 K in lanthanum hydride under high pressures. Nature 569, 528–531 (2019).

[3] Sun, Y., Lv, J., Xie, Y., Liu, H. & Ma, Y. Route to a Superconducting Phase above Room Temperature in Electron-Doped Hydride Compounds under High Pressure. Physical Review Letters 123 (2019)

Contact : florence.levy-bertrand@neel.cnrs.fr