Interlayer charge transfer induced by electronic instabilities in the natural van der Waals hetrostructure 4H$_b$-TaS$_2$

TL;DR

This study investigates how electronic instabilities and charge transfer between layers in the natural van der Waals heterostructure 4H_b-TaS_2 influence its electronic properties, revealing temperature-dependent interlayer charge dynamics and energy gaps.

Contribution

It provides new insights into layer-dependent charge transfer and electronic instabilities in 4H_b-TaS_2, supported by infrared spectroscopy and density functional theory calculations.

Findings

Charge transfer from 1T to 1H layers increases as temperature decreases.

A room-temperature energy gap of approximately 0.35 eV is observed in the 1T layer.

Layer-dependent charge transfer affects the electronic properties of the heterostructure.

Abstract

The natural van der Waals heterostructure 4H$_b$-TaS$_2$ composed of alternating 1T- and 1H-TaS$_2$ layers serves as a platform for investigating the electronic correlations and layer-dependent properties of novel quantum materials. The temperature evolution of the conductivity spectra $\sigma(\omega)$ obtained through infrared spectroscopy elucidates the influence of band modifications associated with the charge-density-wave (CDW) superlattice on the 1T layer, resulting in a room-temperature energy gap, $\Delta_{\rm CDW}\approx$ 0.35 eV. However, there is no gap associated to the 1H layer. Supported by density functional theory calculations, we attribute the behavior of interband transitions to the convergence of the layers, which amplifies the charge transfer from the 1T to the 1H layers, progressing as the temperature decreases. This phenomenon leads to an enhanced low-energy spectral weight and carrier density. The presence of an energy gap and the temperature-tunable charge transfer within the bulk of 4H$_b$-TaS$_2$ driven by layer-dependent CDW states contribute to a more comprehensive understanding of other complex compounds of transition-metal dichalcogenides.