Creating and Detecting Weyl Bosons with Ultracold Fermi Atoms

02.05.2025 12:00 – 13:00

Inspired by investigations of Dirac, Majorana and Weyl fermions in the context of particle, condensed matter and atomic physics, we propose theoretical and experimental platforms to create and detect massless helical boson modes that we call Weyl bosons, the bosonic cousins of Weyl fermions [1]. We show that these exotic excitations arise naturally in one-dimensional interacting Fermi gases, when spin-orbit coupling and Rabi fields are present, through the mixing charge and spin degrees of freedom [2]. We obtain the phase diagram of chemical potential versus Rabi fields for given spin-orbit coupling and interactions, showing regions where zero, one or two types of Weyl bosons exist. We find that, when two types of Weyl bosons emerge, they must propagate with different velocities. Furthermore, we show that the disappearance of any Weyl boson species is described by a topological quantum phase transition of the Lifshitz type, where the velocity of the disappearing Weyl boson vanishes, and the velocity of the surviving Weyl boson develops a cusp at the transition boundary. Lastly, to detect the existence of Weyl bosons, we propose measurements of the dynamic structure factor tensor (charge-charge, charge-spin and spin-spin), where the energy dispersions, spectral weights and helicities of the emergent Weyl bosons may be experimentally extracted in ultracold Fermi systems such as 6Li, 40K, 173Yb and 87Sr.

[1] “Beyond spin-charge separation: Helical modes and topological quantum phase transitions in one-dimensional Fermi gases with spin-orbit and Rabi couplings”, Xiaoyong Zhang and C. A. R. Sá de Melo, arXiv:2405.20255v1 [cond-mat.quant-gas] 30 May 2024.
[2] “From SU(2) to SU(N) fermions with spin-orbit coupling: Open issues beyond charge and spin density waves”, C. A. R. Sá de Melo, lecture delivered (July 11th, 2024) at the Institut Henri Poincaré Symposium on Open questions in the quantum many-body problem: https://www.carmin.tv/en/collections/symposium-open-questions-in-the-quantum-many-body-problem/video/from-su-2-to-su-n-fermions-with-spin-orbit-coupling-open-issues-beyond-charge-and-spin-density-waves

Lieu

Bâtiment: Ancienne Ecole de médecine

salle 74

entrée libre