Geometrical frustration induced (semi-)metal to insulator transition

TL;DR

This paper investigates how geometrical frustration in Hubbard models on pyrochlore and checkerboard lattices induces a transition from (semi-)metallic to insulating states, revealing a spin gap and charge ordering.

Contribution

It combines renormalization group and mean field methods to analyze the MIT in frustrated lattices, providing insights into the pyrochlore system Tl2Ru2O7.

Findings

Metal-insulator transition occurs at half-filling.

Insulating phase has a spin gap without spin symmetry breaking.

Charge ordering is present in the insulating phase.

Abstract

We study the low-energy properties of the geometrically frustrated Hubbard model on a three-dimensional pyrochlore lattice and a two-dimensional checkerboard lattice on the basis of the renormalization group method and mean field analysis. It is found that in the half-filling case, a (semi-)metal to insulator transition (MIT) occurs. Also, in the insulating phase, which has a spin gap, the spin rotational symmetry is not broken, while charge ordering exists. The results are applied to the description of the MIT observed in the pyrochlore system ${\rm Tl_2Ru_2O_7}$.