Séminaire Informel DQMP - Elemental chalcogens as a minimal model for combined charge and orbital order

04.04.2019 11:00 – 13:00

Helices of increased electron density emerging spontaneously in materials containing multiple interacting density waves, are an example of how orbital and charge degrees of freedom may combine to form a single ordered phase. Here we present the elemental chalcogens selenium and tellurium as model materials for the development of combined charge and orbital order. We formulate minimal models capturing the formation of spiral structures in Se and Te, consisting of ordered occupied orbitals and increased charge density. We give descriptions both in terms of a macroscopic Landau theory and a microscopic Hamiltonian. Both reproduce the known chiral crystal structure and are consistent with its observed thermal evolution and behavior under pressure. Extending the model to Po, we shed light on two of its mysterious features: is the only element to crystallise into a simple cubic structure at ambient conditions, and at high temperatures it undergoes a structural phase transition into a less symmetric trigonal configuration. We conclude with a short discussion of how the same type of order arises in transition-metal dichalcogenides, and may be prevalent throughout a much wider class of materials.

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Bâtiment: Ecole de Physique

Salle MaNEP

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