Suppression of the commensurate charge density wave phase in ultrathin 1T−TaS2 evidenced by Raman hyperspectral analysis

Charge Density Wave Vortex Lattice Observed in Graphene-Passivated 1T-TaS2 by Ambient Scanning Tunneling Microscopy

“…The CDW domains observed here are consistent with previous X-ray scattering and STM ,,, data as well as the theoretical model proposed by Nakanishi and Shiba describing the NC-CDW phase of 1T-TaS 2 . Although previous studies have observed the distortion or loss of equilibrium CDW phases in critically thin 1T-TaS 2 films exfoliated onto SiO 2 , the flake presented here (approximately 14 nm thick) is above this thickness and expected to display intrinsic, bulk qualities. ,− The preservation of the intrinsic spatial ordering of the CDW structure in G/TaS 2 suggests that it is possible to study the collective excitations and complex CDW structure of this thin, air-sensitive material through the graphene layer.…”

Patterns and driving forces of dimensionality-dependent charge density waves in 2H-type transition metal dichalcogenides

“…Mechanical exfoliation 8,[17][18][19] , molecular-beam epitaxy (MBE) 7,[20][21][22] , and chemical vapour deposition 23,24 have produced a plethora of 2D materials exhibiting CDWs. Dimensionality reduction has been shown to enhance the CDW order in some of them 8,20,22,24 while suppress it in others 7,18,19,23,25 . Even for the same compound 7,8,20,21 , results from different studies are scattered.…”

Probing charge density wave phases and the Mott transition in $1T$-TaS$_2$ by inelastic light scattering

“…Nearly all of the previously reported results for optical phonons in 1T -TaS 2 are based on Raman spectroscopy on the C-CDW phase and on temperature-dependent measurements in a narrow range around the NC-CDW to C-CDW phase transition [11,13,[15][16][17]. In this article we present temperature-dependent polarization-resolved Raman measurements in the temperature range from 4 K to 370 K covering all three CDW regimes of 1T -TaS 2 .…”

“…Here, the atoms form so called "Star-of-David" clusters. Different studies report either triclinic stacking of these clusters leading to P 1 unit cell symmetry [14], or trigonal or hexagonal stacking and P3 unit cell symmetry [13,[15][16][17]. Factor group analysis predicts 57 A g Raman-active modes with identical polarization-dependence for P 1 unit cell symmetry, and alternatively 19 A g + 19 E g Raman-active modes for P3 unit cell symmetry.…”

“…There is general consensus about the formation of "star-of-David" clusters with in-plane √ 13a × √ 13a lattice reconstruction, whereby twelve Ta atoms are grouped around the 13 th Ta atom [13,14]. In spite of extensive investigations, both experimental and theoretical, it remains an open question whether the stacking of "star-of-David" clusters is triclinic, trigonal, hexagonal or a combination thereof [13][14][15][16][17]. The C-CDW phase is believed to be an insulator [1,[18][19][20] with a gap of around 100 meV [11].…”