Two-Dopant Origin of Competing Stripe and Pair Formation in Hubbard and t-J models*

Understanding the physics of the two-dimensional Hubbard model is widely believed to be a key step in achieving a full understanding of high-T_c cuprate superconductors. In recent years, progress has been made by large-scale numerical simulations and quantum simulation experiments at finite doping and, on the other hand, by microscopic theories able to capture the physics of individual charge carriers. Here, we present our recent work [1] studying single pairs of dopants using the density-matrix renormalization group (DMRG) algorithm. We identify two coexisting charge configurations that couple to the spin environment in different ways: A tightly bound configuration featuring (next-)nearest-neighbor pairs and a stripe-like configuration of dopants accompanied by a spin domain wall. Thus, we establish that the interplay between stripe order and uniform pairing, central to the models’ phases at finite doping, has its origin at the single-pair level. Including a next-nearest-neighbor tunnelling t′ term upsets the balance between the competing stripe and pair states on the two-dopant level.

Based on the pair’s binding energies, we expect the pairing physics to be accessible to state of the art ultracold-atom quantum simulators, which naturally provide access to the higher order correlation functions analyzed in our work.

[1] T. Blatz, U. Schollwöck, F. Grusdt, A. Bohrdt, arXiv:2409.18131 (2024)