Optical study of the charge-density-wave mechanism in 2$H$-TaS$_2$ and Na$_x$TaS$_2$

TL;DR

This study uses optical measurements to analyze the charge-density-wave (CDW) mechanism in 2H-TaS2 and Na-intercalated Na_xTaS2, revealing partial Fermi surface gapping and the interplay between CDW and superconductivity.

Contribution

It provides new optical evidence for the partial gapping of the Fermi surface in 2H-TaS2 and explores the competition between CDW and superconductivity in Na_xTaS2.

Findings

Partial Fermi surface gapping in 2H-TaS2 observed.

Spectral evolution confirms CDW origin of the gap.

Competition between CDW and superconductivity discussed.

Abstract

We report an optical study of transition metal dichalcogenide 2$H$-TaS$_2$ and Na intercalated superconductor Na$_x$TaS$_2$ over a broad frequency range at various temperatures. A clear gap feature was observed for 2$H$-TaS$_2$ when it undergoes a CDW transition. The existence of a Drude component in $\sigma$$_1$($\omega$) below T$_{CDW}$ indicates that the Fermi surface of 2$H$-TaS$_2$ is only partially gapped in CDW state. The spectral evolution of two different Na$_x$TaS$_2$ crystals further confirms that the partial gap structure observed in 2$H$-TaS$_2$ has a CDW origin. The CDW mechanism for 2$H$-TaS$_2$, the competition between CDW and superconductivity in Na$_x$TaS$_2$ system are discussed.