Interlayer coupling driven phase evolution in hyperbolic $1T$-TaS${}_2$

Abstract

Understanding how microscopic interactions control macroscopic phase transitions is central to quantum materials, where charge density waves (CDWs), Mott states, and superconductivity often compete. In $1T$-TaS${}_2$, this competition is tied to a sequence of CDW phases and a hysteretic metal-insulator transition, but details of the transition, especially the role of interlayer coupling, remain unresolved. In this work, spectroscopic ellipsometry is used to determine the uniaxial dielectric response of bulk $1T$-TaS${}_2$ from room temperature down to the commensurate insulating state. The room-temperature data reveal natural type-II hyperbolic behavior in the visible range, with negative in-plane and positive out-of-plane permittivity. Temperature-dependent ellipsometry combined with anisotropic Bruggeman effective medium analysis shows that the metallic domains responsible for percolation evolve from disc-like to needle-like shapes, and that, upon heating, an additional intermediate phase emerges. These results identify the transition in $1T$-TaS${}_2$ as a three-dimensional, interlayer-driven percolation process and establish this material as a natural, tunable hyperbolic medium.

15 pages, 11 figures

References in corpus (12)

• Two Dimensional Atomic Crystals
• Van der Waals heterostructures
• Orbital textures and charge density waves in transition metal dichalcogenides
• Dielectric properties of ultrathin metal films around the percolation threshold
• Band insulator to Mott insulator transition in 1T-TaS${}_2$
• Disrupted orbital order and the pseudo-gap in layered 1T-TaS${}_2$
• Phonon anomaly at the charge ordering transition in 1T-TaS2
• Microscopic nature of the asymmetric hysteresis in the insulator-metal transition of VO${}_2$ revealed by spectroscopic ellipsometry
• Charge density wave surface reconstruction in a van der Waals layered material
• Origin of Distinct Insulating Domains in the Layered Charge Density Wave Material 1T-TaS2
• Interlayer Hopping between Surface Mott Insulator and Bulk Band Insulator in layered 1T-TaS_{2}
• Interplay of broken symmetry and delocalized excitations in the insulating state of 1$T$-TaS${}_2$