Charge ordered phases in the hole-doped triangular Mott insulator 4Hb-TaS2

TL;DR

This study investigates charge ordering in 4Hb-TaS2, a layered material with potential unconventional superconductivity, revealing how inter-layer charge transfer influences its electronic phases and superconducting properties.

Contribution

It provides the first detailed STM/S analysis of charge-ordered phases in 4Hb-TaS2, highlighting the role of Coulomb interactions in driving charge order in a doped triangular Mott insulator.

Findings

Energy gap exhibits out-of-phase relation with charge density.

Charge ordering driven by Coulomb repulsion.

Insulating layer influences superconductivity enhancement.

Abstract

4Hb-TaS2 has been proposed to possess unconventional superconductivity with broken time reveral symmetry due to distinctive layered structure, featuring a heterojunction between a 2D triangular Mott insulator and a charge density wave metal. However, since a frustrated spin state in the correlated insulating layer is susceptible to charge ordering with carrier doping, it is required to investigate the charge distribution driven by inter-layer charge transfer to understand its superconductivity. Here, we use scanning tunneling microscopy and spectroscopy (STM/S) to investigate the charge ordered phases of 1T-TaS2 layers within 4Hb-TaS2, explicitly focusing on the non-half-filled regime. Our STS results show an energy gap which exhibits an out-of-phase relation with the charge density. We ascribe the competition between on-site and nonlocal Coulomb repulsion as the driving force for the charge-ordered insulating phase of a doped triangular Mott insulator. In addition, we discuss the role of the insulating layer in the enhanced superconductivity of 4Hb-TaS2.