Selective Electron–Phonon Coupling in Dimerized 1T-TaS<sub>2</sub> Revealed by Resonance Raman Spectroscopy
Sérgio L. L. M. Ramos, Bruno R. Carvalho, Raphael Longuinhos, Jenaina Ribeiro‐Soares, Cristiano Fantini, Henrique B. Ribeiro, Laurent Molino, Ryan Plumadore, Tony F. Heinz, Adina Luican‐Mayer, M. A. Pimenta
Abstract
The layered transition-metal dichalcogenide material 1T-TaS 2 possesses successive phase transitions upon cooling, resulting in strong electron–electron correlation effects and the formation of charge density waves (CDWs). Recently, a dimerized double-layer stacking configuration was shown to form a Peierls-like instability in the electronic structure. To date, no direct evidence for this double-layer stacking configuration using optical techniques has been reported, in particular through Raman spectroscopy. Here, we employ a multiple excitation and polarized Raman spectroscopy to resolve the behavior of phonons and electron–phonon interactions in the commensurate CDW lattice phase of dimerized 1T-TaS 2 . We observe a distinct behavior from what is predicted for a single layer and probe a richer number of phonon modes that are compatible with the formation of double-layer units (layer dimerization). The multiple-excitation results show a selective coupling of each Raman-active phonon with specific electronic transitions hidden in the optical spectra of 1T-TaS 2, suggesting that selectivity in the electron–phonon coupling must also play a role in the CDW order of 1T-TaS 2 .