Geometric Frustration Assisted Kinetic Ferromagnetism in Doped Mott Insulators

TL;DR

This paper uncovers a microscopic mechanism for itinerant ferromagnetism in doped Mott insulators on frustrated triangular lattices, highlighting the role of doublon-singlon exchange at intermediate coupling and finite doping.

Contribution

It introduces a detailed analysis of the microscopic processes driving ferromagnetism in doped Mott insulators on frustrated lattices, combining DMRG and mean-field methods.

Findings

Ferromagnetism appears at intermediate coupling near 50% doping.

Doublon-singlon exchange drives the fully polarized ferromagnetism.

Ferromagnetism persists under magnetic anisotropy.

Abstract

Understanding ferromagnetism mechanism in doped Mott insulators on frustrated lattices remains challenging at intermediate coupling and finite doping. Here, we study the itinerant ferromagnetism and propose its mechanism in doped Mott insulators on a geometrically frustrated triangular lattice. Using large-scale density matrix renormalization group (DMRG) and unrestricted Hartree-Fock mean-field methods, we reveal that itinerant ferromagnetism appears at intermediate coupling ($10\lesssim U\ll\infty$) near 50% electron doping in the triangular-lattice Hubbard model. By analyzing all microscopic hopping processes, we find that doublon-singlon exchange alone drives the fully polarized ferromagnetism and uncovers the particle-hole asymmetry. We also establish the magnetic phase diagram and compare local spin correlations with recent experiments. Random phase approximation and DMRG calculations consistently confirm that the ferromagnetism persists when $SU(2)$ symmetry is explicitly broken by magnetic anisotropy. These results clarify a microscopic route to itinerant ferromagnetism at intermediate coupling and finite doping in doped Mott insulators.