Influence of structural defects on charge density waves in 1T-TaS2

Abstract

The influence of intrinsic defects of 1T-TaS2 on charge density waves (CDWs) is studied using scanning tunneling microscopy and spectroscopy (STM, STS), angle-resolved photoelectron spectroscopy (ARPES), and density functional theory (DFT). We identify several types of structural defects and find that most have a local character limited to a single CDW site, with a single exception which effectively behaves as a dopant, leading to band-bending and affecting multiple neighboring sites. While only one type of defect can be observed by STM topographic imaging, all defects are easily resolved in STS mapping. Our results indicate modulation of the Mott band gap commensurate with the CDW and breaking of the three-fold symmetry of electronic states. DFT calculations (with included Coulomb interactions) are used to investigate the electronic structure, focusing on both sulfur vacancy and oxygen-sulfur substitution. The sulfur vacancy system, characterized with a metallic behavior, is identified as the origin of one of the experimentally observed defects. Additionally, the effect of oxidation of 1T-TaS2 depends on the substitution site, leading to the heterogeneity of electronic properties.

Observation of the metallic mosaic phase in 1T−TaS2 at equilibrium

“…As a full taxonomy of native surface defects on TaS 2 is not available in the literature and is beyond the scope of this work, we cannot definitively identify the defects in our samples. We can still note certain similarities between the STS spectra we measure and those obtained at Ti substitution 064005-5 [29] and S vacancy [41] sites. In contrast to these previous measurements, we do however only observe a partial closing of the gap for the defects in our samples.…”

Origin of Distinct Insulating Domains in the Layered Charge Density Wave Material 1T‐TaS2

“…The upward band bending near the intrinsic defects is a typical screening behavior against acceptor‐type dopants in the insulating material. [ 30 ] Taken together, we conclude that domains with distinct all‐dimerized configurations exist and while their defect densities are not crucial in determining their stacking orders, they do influence their Fermi levels ( E F ).…”

“…A representative STM image (Figure 1b ) shows the SD clusters as bright protrusions (inset). The dark spots in the STM image acquired at −400 mV are intrinsic defects related to sulfur (S) vacancies [ 29 , 30 ] whose features are more enhanced at the lower bias due to their in‐gap states (Figure S1 , Supporting Information). Figure 1c shows a representative differential conductance (d I /d V ) spectrum acquired at a region away from intrinsic defects.…”

Multifunctional terahertz device based on plasmon-induced transparency

“…To enhance the electromagnetic properties and increase the versatility of materials, the integration of metamaterials with active elements such as semiconductors [13][14][15], phase change materials [16,17], and twodimensional (2D) substances [18][19][20] has been explored by researchers. Graphene, a novel 2D material, which is composed of a hexagonal lattice of carbon atoms resembling a honeycomb structure [21][22][23].…”