Plasmons in the van der Waals charge-density-wave material 2H-TaSe2

TL;DR

This study demonstrates tunable localized plasmons in the 2D charge-density-wave material 2H-TaSe2 across a broad spectral range, revealing effects of interband screening and CDW-related temperature dependence, opening new avenues for plasmonic applications.

Contribution

First experimental observation of tunable localized plasmons in 2H-TaSe2, a correlated 2D CDW material, with insights into screening effects and temperature-dependent behavior.

Findings

Plasmon resonance covers from terahertz to telecom wavelengths.

Plasmon dispersion flattens at large wave vectors due to interband screening.

Anomalous temperature dependence of plasmon resonances linked to CDW excitations.

Abstract

Plasmons in two-dimensional (2D) materials beyond graphene have recently gained much attention. However, the experimental investigation is limited due to the lack of suitable materials. Here, we experimentally demonstrate localized plasmons in a correlated 2D charge-density-wave (CDW) material: 2H-TaSe2. The plasmon resonance can cover a broad spectral range from the terahertz (40 {\mu}m) to the telecom (1.55 {\mu}m) region, which is further tunable by changing thickness and dielectric environments. The plasmon dispersion flattens at large wave vectors, resulted from the universal screening effect of interband transitions. More interestingly, anomalous temperature dependence of plasmon resonances associated with CDW excitations is observed. In the CDW phase, the plasmon peak close to the CDW excitation frequency becomes wider and asymmetric, mimicking two coupled oscillators. Our study not only reveals the universal role of the intrinsic screening on 2D plasmons, but also opens an avenue for tunable plasmons in 2D correlated materials.