Exploring Competing Broken Symmetry States in Quantum Anharmonic Materials

The current proposal is the continuation of the multi-year project (proposal id: 2021240020) approved in the 23rd PRACE call and carried out for the first year (from 1st of October 2021 to 15th of October 2022) on the supercomputer Joliot-Curie.

The project is a three year one aiming at studying the effect of temperature, pressure and ultrafast light absorption and their implication for the structural properties in materials displaying giant quantum-anharmonic effects. Materials of choices are thermoelectrics, ferroelectrics, high-Tc superconductors made of light atoms such as hydrogen and systems in which quantum structural transitions can be induced and shaped by ultrafast absorption of light (charge density waves, phase change materials).

All these fields are key scientific and societal challenges in Europe: energy and the development of a green economy is the pillar of the last European green deal call, the study of structural and superconducting instabilities is one of the main topic of the Graphene flagship project and, finally, the synthesis of hydrogen-based room temperature superconductors made of hydrogen has occurred to a great extent in European universities.

In the first year, in accordance with the program outlined in the first version and with the report submitted, we study the following key topics:

1. Light induced structural transitions in 2 dimensional materials (1TVSe2 and other low dimensional dichalcogenides) and light induced magnetism in quasi 2D materials (V2O5)
2. Thermoelectrics and materials for energy: we have (i) optimized the power conversion efficiency of metal halide perovskite (for example CsSnI3) for photovoltaic application and (ii) we have developed a solid theoretical scheme to calculate the thermoelectric properties of materials at very low dopant concentrations and we have validated it in several prototype compounds.
3. Superhydrides: we studied La-B-H ternary hydrides and we have studied the phase diagram of BaH12 upon Li and Be doping and we have shown that LiBaH12 and BeBaH12 ternary hydrides can be thermodynamically stable against decomposition.

In the second year we plan (i) to study ultrafast melting and phase transition in phase change materials and tetrahedral semiconductors induced by ultrafast light pulses, (ii) investigate technologically relevant materials for thermoelectrics and photovoltaics and (iii) extend the search of superconducting superhydrides to other ternary systems.