Quantum simulations with ultracold fermions in triangular optical lattices have recently emerged as a new platform for studying magnetism in frustrated systems. Experimental realizations of the Fermi Hubbard model revealed striking contrast between magnetism in bipartite and triangular lattices. In bipartite lattices magnetism peaks at half filling, and doped charge carriers tend to suppress magnetic correlations. In triangular lattices for large $U/t$ , magnetism is enhanced by doping away from $n=1$ because kinetic energy of dopants can be lowered through developing magnetic correlations. This corresponds to formation of magnetic polarons, with hole and doublon doping resulting in antiferro- and ferromagnetic polarons respectively. Snapshots obtained with quantum gas microscopes revealed formation of magnetic polarons around dopants at temperatures exceeding the superexchange energy scale. In this work we discuss theoretically that additional insight into properties of magnetic polarons can be achieved using spectroscopic experiments with ultracold atoms. We consider starting from a spin polarized state with small hole doping and applying a two-photon Raman photoexcitation, which transfers atoms into a different spin state. We show that such magnon injection spectra exhibit a separate peak corresponding to formation of a bound state between a hole and a magnon. This polaron peak is separated from the simple magnon spectrum by energy proportional to single particle tunneling and can be easily resolved with currently available experimental techniques. For some momentum transfer there is an additional peak corresponding to photoexciting a bound state between two holes and a magnon. We point out that in two component Bose mixtures in triangular lattices one can also create dynamical magnetic polarons, with one hole and one magnon forming a repulsive bound state.Quantum simulations with ultracold fermions in triangular optical lattices have recently emerged as a new platform for studying magnetism in frustrated systems. Experimental realizations of the Fermi Hubbard model revealed striking contrast between magnetism in bipartite and triangular lattices. In bipartite lattices magnetism peaks at half filling, and doped charge carriers tend to suppress magnetic correlations. In triangular lattices for large $U/t$, magnetism is enhanced by doping away from $n=1$ because kinetic energy of dopants can be lowered through developing magnetic correlations. This corresponds to formation of magnetic polarons, with hole and doublon doping resulting in antiferro- and ferromagnetic polarons respectively. Snapshots obtained with quantum gas microscopes revealed formation of magnetic polarons around dopants at temperatures exceeding the superexchange energy scale. In this work we discuss theoretically that additional insight into properties of magnetic polarons can be achieved using spectroscopic experiments with ultracold atoms. We consider starting from a spin polarized state with small hole doping and applying a two-photon Raman photoexcitation, which transfers atoms into a different spin state. We show that such magnon injection spectra exhibit a separate peak corresponding to formation of a bound state between a hole and a magnon. This polaron peak is separated from the simple magnon spectrum by energy proportional to single particle tunneling and can be easily resolved with currently available experimental techniques. For some momentum transfer there is an additional peak corresponding to photoexciting a bound state between two holes and a magnon. We point out that in two component Bose mixtures in triangular lattices one can also create dynamical magnetic polarons, with one hole and one magnon forming a repulsive bound state.

arXiv:2312.00768Dec 1, 20230 citations

Kinetic magnetism and stripe order in the antiferromagnetic bosonic t − J model

Timothy J. Harris, Ulrich Schollwöck, Annabelle Bohrdt +1 more

Unraveling the microscopic mechanisms governing the physics of doped quantum magnets is key to advancing our understanding of strongly correlated quantum matter. Quantum simulation platforms, e.g., ultracold atoms in optical lattices or tweezer arrays, provide a powerful tool to investigate the interplay between spin and charge motion in microscopic detail. Here, in a twist, we disentangle the role of particle statistics from the physics of strong correlations by exploring the strong coupling limit of doped bosonic quantum magnets, specifically the antiferromagnetic (AFM) bosonic t − J model. Using large-scale density matrix renormalization group calculations, we map out the phase diagram on the two-dimensional square lattice at finite doping. In the low-doping regime, bosonic holes form partially filled stripes, akin to those observed in high- T c cuprates. As doping increases, a transition occurs to a partially polarized ferromagnetic (FM) phase, driven by the motion of mobile bosonic charge carriers forming Nagaoka polarons. At high doping or large t / J , the system evolves into a fully polarized FM. These findings shed light on the role of particle statistics in strongly correlated many-body systems, revealing connections to stripe formation and the physics of kinetic (Nagaoka-type) ferromagnetism. Our results may be realized in state-of-the-art quantum simulation platforms, including bosonic quantum gas microscopes, Rydberg atom tweezer arrays, and ultracold polar molecules, paving the way for future experimental studies of doped bosonic quantum magnets.Unraveling the microscopic mechanisms governing the physics of doped quantum magnets is key to advancing our understanding of strongly correlated quantum matter. Quantum simulation platforms, e.g., ultracold atoms in optical lattices or tweezer arrays, provide a powerful tool to investigate the interplay between spin and charge motion in microscopic detail. Here, in a twist, we disentangle the role of particle statistics from the physics of strong correlations by exploring the strong coupling limit of doped bosonic quantum magnets, specifically the antiferromagnetic (AFM) bosonic t − J model. Using large-scale density matrix renormalization group calculations, we map out the phase diagram on the two-dimensional square lattice at finite doping. In the low-doping regime, bosonic holes form partially filled stripes, akin to those observed in high- T c cuprates. As doping increases, a transition occurs to a partially polarized ferromagnetic (FM) phase, driven by the motion of mobile bosonic charge carriers forming Nagaoka polarons. At high doping or large t / J , the system evolves into a fully polarized FM. These findings shed light on the role of particle statistics in strongly correlated many-body systems, revealing connections to stripe formation and the physics of kinetic (Nagaoka-type) ferromagnetism. Our results may be realized in state-of-the-art quantum simulation platforms, including bosonic quantum gas microscopes, Rydberg atom tweezer arrays, and ultracold polar molecules, paving the way for future experimental studies of doped bosonic quantum magnets.

arXiv:2410.00904Physical review. B./Physical review. BJun 1, 20260 citations

Quantum Magnetism with Ultracold Atoms

Jennie Guzman, Sabrina R. Leslie, Mukund Vengalattore +2 more

Bulletin of the American Physical SocietyMay 29, 20080 citations

U/t

, magnetism is enhanced by doping away from

n=1

because kinetic energy of dopants can be lowered through developing magnetic correlations. This corresponds to formation of magnetic polarons, with hole and doublon doping resulting in antiferro- and ferromagnetic polarons respectively. Snapshots obtained with quantum gas microscopes revealed formation of magnetic polarons around dopants at temperatures exceeding the superexchange energy scale. In this work we discuss theoretically that additional insight into properties of magnetic polarons can be achieved using spectroscopic experiments with ultracold atoms. We consider starting from a spin polarized state with small hole doping and applying a two-photon Raman photoexcitation, which transfers atoms into a different spin state. We show that such magnon injection spectra exhibit a separate peak corresponding to formation of a bound state between a hole and a magnon. This polaron peak is separated from the simple magnon spectrum by energy proportional to single particle tunneling and can be easily resolved with currently available experimental techniques. For some momentum transfer there is an additional peak corresponding to photoexciting a bound state between two holes and a magnon. We point out that in two component Bose mixtures in triangular lattices one can also create dynamical magnetic polarons, with one hole and one magnon forming a repulsive bound state.