Moir\'e in $\Gamma$-valley square lattice: Copper- and iron-based superconductor simulation in a single device

TL;DR

This paper proposes using twisted $ ext{ZnF}_2$ homobilayers to simulate high-$T_c$ superconductor models, revealing potential for realizing strongly correlated phases in $ ext{Moire}$ heterostructures.

Contribution

It introduces a universal framework for simulating cuprate and iron-based superconductor models using $ ext{Gamma}$-valley square-lattice moiré systems, supported by detailed theoretical and computational analysis.

Findings

First moiré band mimics a single-orbital Hubbard model for cuprates.

Second and third moiré bands map to a two-orbital Hubbard model for iron pnictides.

Identified a stable antiferro-orbital, ferromagnetic insulating phase at quarter-filling.

Abstract

Novel superconducting phases have been found in various moir\'e heterostructures based on hexagonal lattices. However, the archetypal high-temperature superconductors (cuprates, iron-based and nickelate families) all share a square lattice foundation. These materials host a rich landscape of correlated phenomena, such as charge and spin stripes, pseudogap behavior, and unconventional metallicity, which continue to challenge our fundamental understanding of strongly correlated electrons. In this work, we investigate the possibility of simulating the effective models governing these high-$T_c$ superconductors using twisted homobilayers of $\Gamma$-valley square-lattice systems. We develop a universal theoretical framework and carry out a detailed analysis of a promising candidate material ZnF$_2$. We find that the first moir\'e band realizes a single-orbital square-lattice Hubbard model, widely believed to capture cuprate physics, while the second and third moir\'e bands map to a $p_x,p_y$ two-orbital square-lattice Hubbard model, which shares common physics to the minimal $d_{xz}, d_{yz}$ models proposed for iron pnictides. Our study combines continuum Hamiltonian modeling, first-principle calculations, and Hartree-Fock mean field theory. The latter focuses on the quarter-filling regime of the two-orbital model and in particular leads to, among others, a stable antiferro-orbital, ferromagnetic insulating phase. These results highlight $\Gamma$-valley square-lattice moir\'e systems as a new and important generation of van der Waals heterostructures to realize interesting strongly correlated phases of matter.