Selective Electron-Phonon Coupling in Dimerized 1T-TaS2 Revealed by Resonance Raman Spectroscopy

The layered transition-metal dichalcogenide material1T-TaS 2 possesses successive phase transitionsuponcooling, resulting in strong electron-electron correlationeffects and the formation of charge density waves (CDWs). Recently,a dimerized double-layer stacking configuration was shown to forma Peierls-like instability in the electronic structure. To date, nodirect evidence for this double-layer stacking configuration usingoptical techniques has been reported, in particular through Ramanspectroscopy. Here, we employ a multiple excitation and polarizedRaman spectroscopy to resolve the behavior of phonons and electron-phononinteractions in the commensurate CDW lattice phase of dimerized 1T-TaS 2 . We observe a distinct behavior from what ispredicted for a single layer and probe a richer number of phonon modesthat are compatible with the formation of double-layer units (layerdimerization). The multiple-excitation results show a selective couplingof each Raman-active phonon with specific electronic transitions hiddenin the optical spectra of 1T-TaS 2 , suggestingthat selectivity in the electron-phonon coupling must alsoplay a role in the CDW order of 1T-TaS2.