## Séminaire de Physique Théorique

**Quartic bosonic metallic state and its topological properties**

Julien Garaud (IDP)

Thursday 03 March 2022 14:00 - -

**Résumé :**

Superconductivity is an ordered quantum state with a long-range coherence of pairs of electrons, the Cooper pairs, which leads to zero resistivity and

diamagnetism. I will present the recent observations of a new state, coined quartic bosonic metal, characterized by fermionic quadrupling correlations. This resistive state has no long-range order between Cooper pairs but only between pairs of pairs.

Unlike the superconductors, which break the U(1) gauge symmetry, this state spontaneously breaks the (discrete) time-reversal symmetry. This leads to unconventional magnetic properties, detected in muon spin rotation experiments and by the appearance of a spontaneous Nernst effect.

I will finally demonstrate that this state can be effectively accounted for, by a Faddeev-Skyrme model for the four-fermion order parameter. Its spectrum of topological excitations is rich, as it hosts domain-walls, magnetic-flux-carrying skyrmions, and most likely hopfions.

**Liens :**