Pressure induced collapse of the charge density wave and Higgs mode visibility in 2H-TaS$_2$

TL;DR

This study investigates how pressure affects charge density waves and Higgs mode visibility in 2H-TaS2, revealing a collapse of the CDW at 8.5 GPa and the first Raman observation of a Higgs mode in this material.

Contribution

It reports the first observation of a Raman-active Higgs mode in 2H-TaS2 and details the pressure-induced collapse of the charge density wave.

Findings

Charge density wave collapses at 8.5 GPa.

Higgs mode coexists with superconductivity.

In-gap superconducting mode observed via Raman spectroscopy.

Abstract

The pressure evolution of the Raman active electronic excitations of the transition metal dichalcogenides 2H-TaS$_2$ is followed through the pressure phase diagram embedding incommensurate charge-density-wave and superconducting states. At high pressure, the charge-density-wave is found to collapse at 8.5~GPa. In the coexisting charge-density-wave and superconducting orders, we unravel a strong in-gap superconducting mode, attributed to a Higgs mode, coexisting with the expected incoherent Cooper-pair breaking signature. The latter remains in the pure superconducting state reached above 8.5~GPa. Our report constitutes the first observation of such Raman active Higgs mode since the longstanding unique case 2H-NbSe$_2$.