Raman Optical Activity of 1T-TaS₂

Abstract

Measurements of optical activity can be readily performed in transparent matter by means of a rotation of transmitted light polarization. In the case of opaque bulk materials, such measurements cannot be performed, making it difficult to assess possible chiral properties. In this work, we present full angular polarization dependencies of the Raman modes of bulk 1T-TaS 2 , which has recently been suggested to have chiral properties after pulsed laser excitation. We found that a mechanical rotation of the sample does not alter polarization-resolved Raman spectra, which can only be explained by introducing an antisymmetric Raman tensor, frequently used to describe Raman optical activity (ROA). Raman spectra obtained under circularly polarized excitation demonstrate that 1T-TaS 2 indeed shows ROA, providing strong evidence that 1T-TaS 2 is chiral under the used conditions of laser excitation. Our results suggest that ROA may be used as a universal tool to study chiral properties of quantum materials.

Spectroscopic visualization and phase manipulation of chiral charge density waves in 1T-TaS2

“…The out-of-plane A 1g Raman modes for the σ+σ+ and σ−σ− configurations are almost the same, whereas the intensities of in-plane E g modes differ remarkably for the σ+σ− and σ−σ+ configurations, indicating that the chiral Raman response may correspond to an in-plane chiral structure. Similar experimental results of chiral Raman response in 1T-TaS 2 have been reported recently, which were well explained by Raman tensor analysis, either by introducing an antisymmetric Raman tensor or including complex Raman tensor elements 28 , 29 .…”

Bridging Structure, Magnetism, and Disorder in Iron-Intercalated Niobium Diselenide, FexNbSe2, below x = 0.25

“…Two linear polarizers were set parallel to each otherone in the incoming laser excitation path and the other in the spectrometer detection pathand a half-wave plate was mounted directly in front of the latter polarizer. Rotating the half-wave plate by θ/2 allowed for the detection of Raman scattered light that was effectively rotated by θ with respect to the polarization vector of the incident laser light . For the space group P 6 3 / mmc and specific Wyckoff positions occupied in the Fe 0.23 NbSe 2 crystal structure, the symmetry-adapted phonon modes (SAMs) expected at the zone-center Γ SL point are: Γ acoustic = A 2u + E 1u and Γ optical = 4A 1g + A 1u + 2A 2g + 5A 2u + 5B 1g + 2B 1u + B 2g + 5B 2u + 5E 1g + 7E 1u + 7E 2g + 6E 2u . − Based on the optical phonons present, the expected Raman-active modes are 4A 1g + 5E 1g + 7E 2g . − As in the unpolarized Raman experiment, the backscattering measurement geometry along the ZZ direction precludes the detection of the E 1g modes for materials with this space group symmetry …”

Quantum Composites with Charge‐Density‐Wave Fillers

“…In bulk 1T-TaS 2 , (purple spectrum), the intense peaks in the range of 70 to 130 cm −1 , as well as the low-intensity peaks in the range of 225 to 400 cm −1 range, are attributed to the zone-folded acoustic and optical phonons. [50][51][52][53] These phonon branches appear because of Brillouin zone reconstruction in the C-CDW phase and disappear during the C-CDW-NC-CDW phase transition. [51] At 93 K, the bulk crystal and the fillers are all in the C-CDW phase.…”

“…Raman spectroscopy is a standard technique for monitoring CDW phase transition owing to its sensitivity to the crystal lattice distortions, reconstruction and phonon folding due to CDW periodicity, and the loss of translation symmetry in the IC-CDW phase. [49][50][51][52][53] The Raman spectra were accumulated in the conventional backscattering configuration at T ≈ 93 K. The Raman laser spot size was ≈1 µm. Experiments were conducted with the minimum laser power to avoid any laser-induced heating effects.…”