Probing the interlayer coupling in 2$H$-NbS$_2$ via soft x-ray angle-resolved photoemission spectroscopy

TL;DR

This study uses soft x-ray ARPES to measure interlayer coupling in 2H-NbS2, revealing how atomic structure influences electronic properties and providing insights relevant for superconductivity in layered materials.

Contribution

It introduces a method to explicitly extract interlayer hopping parameters in NbS2 using SX-ARPES and tight-binding modeling, bridging experimental data with first-principles calculations.

Findings

Visualization of S 3p_z bands dispersing with out-of-plane momentum

Quantitative extraction of interlayer hopping parameters

Clarification of atomic distance effects on interlayer coupling

Abstract

In the large family of two-dimensional (2D) layered materials including graphene, its honeycomb analogs, and transition-metal dichalcogenides, the interlayer coupling plays a rather intriguing role. On the one hand, the weak van der Waals interaction that holds the layers together endows these compounds with quasi-2D properties, which might imply small interlayer effects on the electronically active bands. On the other hand, the oft-witnessed differences in electronic, optical, and magnetic behaviors of monolayers, bilayers, and multilayers of the same compound must have as their microscopic origin the detailed interlayer hopping parameters. Given the few experimental reports that have attempted to explicitly extract these parameters, we employ soft-x-ray angle-resolved photoemission spectroscopy (SX-ARPES) to probe the interlayer coupling in superconducting 2$H$-NbS$_2$. We visualize the S 3$p_z$ bands that disperse with respect to the out-of-plane momentum and introduce a simple tight-binding model to extract the interlayer hopping parameters. From first-principles calculations, we clarify how atomic distances and the proper accounting for screening via hybrid functionals influence these bands. The knowledge of interlayer hopping parameters is particularly pertinent in NbS$_2$, where recent experiments have uncovered fingerprints of finite-momentum superconductivity in the bulk material and heterostructures.