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

Linearized antiferromagnetic spin-wave spectra around a hole in the two-dimensional Hubbard model

Han-Yong Choi

We study the effects of doping on the spin fluctuations of the two-dimensional Hubbard model. Within a harmonic approximation we calculate the linearized antiferromagnetic spin-wave spectra around a hole away from half-filling, which takes the form of a spin polaron in a mean-field approximation. The presence of the spin polaron breaks a symmetry of the problem, the product of time reversal and lattice translation. As a result, the double degeneracy of the magnon spectra of the N\'eel state is lifted. There also appear localized magnon modes depending on the ratio U/t of the Hubbard model. The quantum correction due to the spin fluctuations is found to increase the spin polaron binding energy for U/t13, but decreases it for U/t>13.We study the effects of doping on the spin fluctuations of the two-dimensional Hubbard model. Within a harmonic approximation we calculate the linearized antiferromagnetic spin-wave spectra around a hole away from half-filling, which takes the form of a spin polaron in a mean-field approximation. The presence of the spin polaron breaks a symmetry of the problem, the product of time reversal and lattice translation. As a result, the double degeneracy of the magnon spectra of the N\'eel state is lifted. There also appear localized magnon modes depending on the ratio U/t of the Hubbard model. The quantum correction due to the spin fluctuations is found to increase the spin polaron binding energy for U/t13, but decreases it for U/t>13.

Physical review. B, Condensed matterAug 1, 19917 citations

Many-Polaron States in the Holstein–Hubbard Model

Laurent Proville, S. Aubry

arXiv:cond-mat/0109342Journal of Statistical PhysicsMar 1, 20020 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.