Regensburg 2025 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 6: Phase Transformations

MM 6.2: Talk

Monday, March 17, 2025, 16:00–16:15, H10

Quantum phase diagram of sulfure hydride — •Marco Cherubini and Michele Casula — IMPMC, CNRS, Paris, France

In the recent rush towards room temperature superconductivity, hydrogen-based materials are the most prosiming candidates. Sulfulr hydride exhibits a maximum superconductive critical temperature of about 200K at 150 GPa. To our knowledge, a comprehensive theoretical characterization of the phase diagram of sulfur hydride in a wide temperature range is still missing in literature. To address this, we performed path integral molecular dynamics simulations (PIMD). The description of the low temperature regime has been made feasible by the use a machine learning potential trained on ab-initio data. We found three different regimes. At high pressure, the phase diagram is dominated by a paraelectric phase, with symmetric hydrogen bonds. Reducing the pressure, we observed first a regime characterized by finite local dipole moments and finally, at even lower pressures, the ferroelectric regime. Quantum simulations show that the formation of finite local moments is temperature-independent, unlike the transition to the ferroelectric regime. Classical simulations, by contrast, showed stronger temperature dependence for both the transitions and significantly higher critical pressures, highlighting the impact of quantum nuclear fluctuations.

Keywords: Hydrogen; Nuclear Quantum Effects; High pressure phyiscs; Path Integral Molecular Dynamics; Anharmonicity