Prediction of high-temperature superconductivity in LaH4 at low pressures

Superconducting hydrides have received significant attention in the last decade due to their potential for room-temperature superconductivity. However, achieving high critical temperatures (T_cs) typically requires extreme pressures exceeding 150 GPa. Recently, a new, low-pressure Rm-LaH₄ phase was observed to form above approximately 20 GPa. Here, we perform first-principles calculations to investigate the electron–phonon interactions and superconducting properties of the new phase across a range of pressures. At the harmonic level, the system is found to be dynamically unstable, but this is remedied through the inclusion of anharmonic effects. We estimate that T_c reaches up to 115 K at 25 GPa, driven by a high density of states at the Fermi level (N_F) and soft phonon modes. However, superconductivity is suppressed with increasing pressure, as T_c rapidly decreases to 34 K at 60 GPa and 11 K at 100 GPa, due to a reduction in N_F and phonon hardening.