Metal-insulator transition and intermediate phases in the kagome lattice Hubbard model

TL;DR

This study uses DMRG to explore the ground states of the kagome lattice Hubbard model at half-filling, revealing multiple phases including metallic, insulating, and quantum spin liquid states, with a continuous metal-insulator transition.

Contribution

It provides the first detailed numerical phase diagram of the half-filled kagome Hubbard model, identifying intermediate phases and transition types, advancing understanding of kagome materials.

Findings

Identified a metal-insulator transition around U_c1.

Discovered two insulating intermediate phases: translational symmetry breaking and quantum spin liquid.

Confirmed the robustness of phases across different system widths.

Abstract

Motivated by the recent discovery of metallic kagome lattice materials, AV$_{3}$Sb$_{5}$ (A=K, Rb, Cs), we investigate the ground state of the half-filled kagome lattice Hubbard model by employing the density-matrix renormalization group (DMRG) method. We identify a metal-insulator transition around $U \thicksim U_{c1}$ and four distinct phases as a function of $U/t$ on narrower cylinders, including a metallic phase at $U < U_{c1}$, two insulating intermediate phases: a translational symmetry breaking phase at $U_{c1} < U < U_{c2}$ and a quantum spin liquid phase at $U_{c2} < U < U_{c3}$, and the kagome antiferromagnetic phase at $U>U_{c3}$. We confirm that the translational symmetry breaking phase is robust for wider cylinders, while the quantum spin liquid phase is smoothly connected to the kagome antiferromagnetic phase with increasing the system width. Moreover, our numerical observations indicate a continuous metal-insulator transition at $U_{c1}$, whose nature is consistent with Slater's transition scenario. The magnetic phase transition between two insulating intermediate phases at $U_{c2}$ is first order. Our findings may provide insights into exotic kagome lattice materials.