Group seminar at MPQ and Zoom: Kinetic magnetism and stripe order in the antiferromagnetic bosonic t −J model
Tim Harris, LMU Munich, Germany
Group seminar at MPQ lecture hall and Zoom
Tuesday, 25 February, 09:00 am (MEZ)
Unraveling the complex interplay between spin and charge degrees-of-freedom in strongly correlated systems is a key challenge in quantum many-body physics. In particular, the role of kinetic exchange mechanisms in stabilizing long-range ferromagnetic (FM) order in doped Mott insulators and other strongly correlated materials—especially at finite doping and away from known theoretical limits [1]—remains an intriguing open question. Recent quantum simulations of the 2D Fermi-Hubbard model in kinetically frustrated moire heterostructures [2, 3] and ultracold fermionic gases in triangular optical lattices [4, 5] have revealed striking evidence for the emergence of magnetic phases driven by kinetic effects, underscoring the need for a deeper theoretical understanding of such phenomena.
In this talk, I will present our recent results investigating the emergence of kinetic magnetism in the antiferromagnetic (AFM) bosonic t−J model, using large-scale density matrix renormalization group (DMRG) simulations to map out the T = 0 phase diagram on the 2D square lattice at finite doping [6]. Specifically, we identify a transition from AFM to FM ordered ground states as a function of doping δ and t/J, driven by the proliferation of so-called Nagaoka polarons throughout the system—i.e., mobile holes bound to localized FM regions. These polarons are a hallmark of the competition between kinetic and magnetic exchange mechanisms in doped Mott insulators and may be directly imaged in ultracold atom quantum simulators´ via site-resolved snapshots of the many-body wavefunction. Additionally, I will comment on signatures of partially-filled stripe order which emerges in the low-doping regime, providing evidence of a connection between our results and the strongly correlated phases of the 2D Fermi-Hubbard and t −J models.
Our findings establish the AFM bosonic t−J model as a minimal setting for studying kinetic magnetism in strongly correlated many-body systems and provide a theoretical foundation for future experimental realizations in bosonic quantum gas microscopes, where the preparation of negative absolute temperature states enables the realization of local AFM superexchange couplings [7].
[1] Y. Nagaoka, Phys. Rev. 147, 392-405 (1966).
[2] L. Ciorciaro et. al., Nature 623, 509-513 (2023).
[3] Z. Tao et. al., Nat. Phys. 20, 783–787 (2024).
[4] M. Lebrat et. al., Nature 629, 317-322 (2024).
[5] M. L. Prichard et. al., Nature 629, 323-328 (2024).
[6] T. J. Harris et. al., arXiv:2410.00904 (2024).
[7] A. Bohrdt*, D. Wei* et. al., arXiv.2410.19500 (2024).