From band insulator to Mott insulator in one dimension

TL;DR

This paper analyzes a one-dimensional ferroelectric perovskite model, revealing a phase diagram with a dimerized phase separating band and Mott insulators, characterized by a critical transition and specific excitation properties.

Contribution

It provides a detailed phase diagram for the model, identifying the nature of phase transitions and excitation behaviors, which was not previously established.

Findings

Identification of a dimerized phase separating insulator types

The transition from band to dimerized insulator is Ising critical

Charge gap vanishes and optical conductivity diverges at transition

Abstract

We derive the phase diagram for the one-dimensional model of a ferroelectric perovskite recently introduced by Egami, Ishihara and Tachiki [Science, {\bf 261}, 1307 (1993)]. We show that the interplay between covalency, ionicity and strong correlations results in a spontaneously dimerized phase which separates the weak-coupling band insulator from the strong-coupling Mott insulator. The transition from the band insulator to the dimerized phase is identified as an Ising critical point. The charge gap vanishes at this single point with the optical conductivity diverging as $\sigma(\omega)\sim \omega^{-3/4}$. The spin excitations are gapless above the second transition to the Mott insulator phase.