Dynamics of Charge-Density-Wave puddles in 2$H$-NbSe$_2$

TL;DR

This study investigates the dynamic behavior of charge-density-wave puddles in 2H-NbSe2 using Raman and time-resolved reflectivity, revealing a Fano-coupled phonon-CDW hybrid mode that influences CDW stability.

Contribution

It uncovers a new Fano-coupled phonon-CDW hybrid mode and elucidates puddle dynamics in 2H-NbSe2, advancing understanding of CDW behavior in layered quantum materials.

Findings

Identification of a Fano-coupled phonon-CDW hybrid mode.

Observation of a low-frequency overdamped oscillation at ~17 K.

Insights into lattice pinning and electronic correlation effects on CDW order.

Abstract

Electronic phases in quantum materials are often governed by nanoscale inhomogeneity, where local order develops within spatially confined regions or puddles. A prominent example is an incommensurate charge-density-wave (I-CDW) that comprises locally commensurate domains. In 2$H$-NbSe$_2$, such an I-CDW state persists alongside lattice anharmonicity and superconductivity, raising fundamental questions about the dynamical stabilization of CDW order in puddles. Here, we probe the puddle-dynamics in 2$H$-NbSe$_2$. Raman scattering reveals a strong Fano-coupling between the interlayer shear vibration and the CDW amplitude mode. Time-resolved reflectivity measurement shows a low-frequency ~0.15 THz coherent overdamped oscillation onsetting within the CDW regime at ~17 K, pointing towards a so far unexplored transition. This we identify as a Fano-coupled phonon-CDW hybrid emerging from the collective dynamics of CDW puddles. These dynamics highlight how lattice pinning and electronic correlations in layered materials affect the CDW order, which is crucial for the design of novel Van der Waals devices.