Manipulating exciton binding by floquet engineering ‌in Fermi Hubbard ladder

M. Sarkar,1 Z. Lenarcic,1 D. Golez1

1Jozef Stefan Institute, SI-1000, Ljubljana, Slovenia

Strong excitations of correlated quantum materials give rise to various non-thermal phases which are not present in their equilibrium counterpart. Recently, it was shown that the one-dimensional Fermi Hubbard Model features charge density wave and η-pairing phases upon photo-doping. In this study, we explore the non-equilibrium behavior of the Fermi Hubbard ladder and employ the Schrieffer-Wolff transformation to map it to a simplified t-J-like model, providing an effective equilibrium description of the photo-doped states. Our investigation highlights the significance of applying an electric field along the rung to the hopping term. This floquet manipulation allows to increase the spin and η-exchange coupling along the rung independent of the hopping term. Moreover, the magnitude of hopping decreases as a result of the drive. These combined effect tends to localize the excitons close to each other and thus enhance its binding energy. To characterize the ground state of the system, we employ relevant correlators and make notable observations. We show that at certain drive frequencies, the ground state encompasses a strongly bound holon-holon/doublon-holon pair along the rung, alongside inter-chain singlets. Additionally, we propose experimental setups to test our theory.