Effects of Long-Range Correlations on Nonmagnetic Mott Transitions in Hubbard model on Square Lattice

TL;DR

This study investigates the Mott transition in the Hubbard model on a square lattice, emphasizing the role of long-range D-H correlations and introducing a new length scale framework to understand the transition mechanism.

Contribution

It introduces a novel length scale analysis of D-H binding and D-D factors, providing a renewed understanding of the Mott transition without magnetic or superconducting correlations.

Findings

Mott transitions occur near the band width with various D-H binding factors.

The transition is characterized by the equality of D-H binding length and D-D distance.

D-D factors have a minor impact on the Mott transition.

Abstract

The mechanism of Mott transition in the Hubbard model on the square lattice is studied without explicit introduction of magnetic and superconducting correlations, using a variational Monte Carlo method. In the trial wave functions, we consider various types of binding factors between a doubly-occupied site (doublon, D) and an empty site (holon, H), like a long-range type as well as a conventional nearest-neighbor type, and add independent long-range D-D (H-H) factors. It is found that a wide choice of D-H binding factor leads to Mott transitions at critical values near the band width. We renew the D-H binding picture of Mott transitions by introducing two characteristic length scales, the D-H binding length l_{DH} and the minimum D-D distance l_{DD}, which we appropriately estimate. A Mott transition takes place at l_{DH}=l_{DD}. In the metallic regime (l_{DH}>l_{DD}), the domains of D-H pairs overlap with one another, thereby doublons and holons can move independently by exchanging the partners one after another. In contrast, the D-D factors give only a minor contribution to the Mott transition.