Abstract
Charge density wave (CDW) is a unique phenomenon mostly realized in two-dimensional (2D) metallic layered transition metal dichalcogenides (TMDCs). Here, we report on Raman spectroscopy of single crystal 1T-VSe2 and observed signature of commensurate CDW (C-CDW) and incommensurate (I-CDW) transition, in the temperature range of 50-120 K. The room temperature Raman spectra showed a sharp A1g mode ~ 206 cm-1 along with two new weak and broad Raman modes associated to Eg mode ~ 257 cm-1 and two-phonon mode (2ph) ~ 332 cm-1. The onset of I-CDW and C-CDW is estimated from resistance measurements supported by magnetic measurements. Remarkably, at the onset of I-CDW ~ 115 K, a significant enhancement in the intensity of weak Eg mode is observed along with emergence of a doubly degenerate Eg(2) mode ~ 144 cm-1. Below 70 K, a weak A1g mode ~ 170 cm-1 emerged signifying the onset of C-CDW. Anomalous phonon softening of Eg mode ~ 257 cm-1 and 2ph process mode below I-CDW has been also observed, which is signifying the involvement of electron-phonon coupling.
Highlights
The charge density wave (CDW) is a low-temperature ordered phase that arises from periodic modulation of conduction electron densities accompanied by periodic distortion of the atomic lattice [1,2,3]
The novel phenomenon of the CDW has been investigated in single crystalline 1T-VSe2 using temperaturedependent resistance measurement and Raman spectroscopy
The hump in resistance measurement below 110 K is related to the onset of the incommensurate CDW (I-CDW), while the existence of the CCDW ∼ 50 K is confirmed by dR/dT
Summary
The charge density wave (CDW) is a low-temperature ordered phase that arises from periodic modulation of conduction electron densities accompanied by periodic distortion of the atomic lattice [1,2,3]. Among the several versatile properties, the CDW is a novel phenomenon realized in 1T and 2H polytypes of many metallic layered TMDCs, such as NbSe2, TaSe2, TaS2, VTe2, and VSe2 [14,15,16,17,18,19,20] These materials have received much scientific and technological attention for many-body interactions and potential applications in memory devices, transistors, logic-gate electronics, and oscillators [14,15,16,17,18,19,20]. In this paper, we have studied the electron-phonon coupling driven CDW transitions in bulk single crystal 1T-VSe2, using temperaturedependent resistivity, magnetic susceptibility, and Raman spectroscopy measurements. The coupling between electron and phonon, at low temperatures, is demonstrated from resistivity as well as magnetic measurements, while spectroscopy is used as a tool to access the CDW in VSe2
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