Designing Flat Bands, Localized and Itinerant States in TaS2 Trilayer Heterostructures

TL;DR

This paper proposes a novel T/T/H trilayer heterostructure combining flat band insulators and metallic layers, enabling the study of strong correlation effects and potential unconventional superconductivity through stacking configuration control.

Contribution

It introduces a new trilayer design that maintains localized spins and explores the transition from doped Mott insulator to Kondo insulator by stacking variation.

Findings

Charge transfer removes Mottness in bilayers

Localized spins persist in the flat band of T/T bilayer

Stacking variations enable crossover from Mott to Kondo insulator

Abstract

Stacking and twisting van der Waals materials provide a powerful tool to design quantum matter and engineer electron correlation. For instance, monolayers of 1T- and 1H-TaS2 are Mott insulating and metallic (also superconducting), respectively, and thus, the T/H bilayer systems have been extensively investigated in the context of heavy fermions and unconventional superconductivity, which are expected phases from localized spins (1T) coexisting with itinerant electrons (1H). However, recent studies revealed that significant charge transfer from the 1T to 1H layers removes the 1T Mottness and renders the above scenario elusive. In this work, we propose a T/T/H trilayer heterostructure by combining a T/T bilayer -- which is a band insulator with flat dispersion -- with a 1H layer. After charge redistribution, this trilayer heterostructure shows localized spins in the Mott flat band of the T/T bilayer and weak spin polarization in the metallic H layer. We argue that by varying the stacking configurations of the T/T bilayer in the T/T/H trilayer, a crossover from a doped Mott insulator to a Kondo insulator can be achieved. The T/T/H trilayer provides therefore a rich novel heterostructure platform to study strong correlation phenomena and unconventional superconductivity.