Calendario Attività
 

Emergence of a fermion quadrupling condensate that spontaneously breaks time- reversal symmetry.

Categoria
Seminario
Data
2022-07-18 15:00 - 16:00
Luogo
14 - 15 IV piano St. 9
Affiliation
Department of Physics, Stockholm University
Area di Ricerca
Transizioni di fase, Sistemi condensati e a molti corpi, Fisica Statistica e loro applicazioni

Superconductivity arises as a consequence of the formation and condensation of electron pairs. However, multicomponent systems may exhibit a different kind of order associated with the condensation of fermionic quadruplets. In this seminar, I will present the first experimental observation in of a fermion quadrupling condensate, above the superconducting transition, that breaks time-reversal symmetry [1]. From a theoretical standpoint, this is a beyond mean-field state whose onset is driven by the proliferation of topological phase excitations. Studying the interplay between the different pological defects at play is a highly nontrivial problem that can be addressed via Monte Carlo simulations. In the second part of my talk, I will show how the emergence of this phase has been systematically investigated within a London model for s+is superconductors as a function of different intercomponent couplings [2]. Finally, I will briefly discuss the case of magic-angle twisted bilayer graphene, whose low-energy effective model has revealed a beyond-mean field phase diagram with a substantial fermionic quadrupling state for all the values of the parameters considered [3]. [1]V. Grinenko et. al., ?State with spontaneously broken time-reversal symmetry above the superconducting phase transition?, Nature Physics 17, 1254?1259 (2021). [2] I. Maccari, E. Babaev, ?Effects of intercomponent couplings on the appearance of time-reversal-symmetry-breaking fermion quadrupling state in two-component London model? arXiv preprint arXiv:2202.02269 [3] I. Maccari, J. Carlstr?m, E. Babaev, ?Possible time-reversal-symmetry-breaking fermionic quadrupling condensate in twisted bilayer graphene?, arXiv preprint arXiv:2206.02698

 
 

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