Lattice Vibrations in the Charge‐Density‐Wave States of Layered Transition Metal Dichalcogenides

Abstract

Contents Zntroduction2. Renormalization of the phonon energy due to the electron-phonon interaction 3. Raman scattering process in materials with CDW phase transitions 3.1 Raman scattering process in metals 3.2 Raman scattering process due to the CDW modes 3.3 Two-phonon Ranian process from the Kohn anomaly modes 4.1 1T-TiSe,, lT-Til -zV2Sez, and 1T-TiS,

Femtosecond snapshots of gap-forming charge-density-wave correlations in quasi-two-dimensional dichalcogenides1T−TaS2and2HDemšar1, Forró2, Berger3 et al. 2002Phys. Rev. B1359991View full textAdd to dashboardCite

“…The T -dependence of ω A and Γ A determined from the fit are plotted in Fig. 2a) showing excellent agreement with the established Raman data [14]. Γ A strongly increases near T c−nc .…”

“…In contrast, for 2H-TaSe 2 the T -dependence of ω A and Γ A (Fig. 2b)) is much more mean-field like, becoming overdamped (ω A ≃ Γ A ) around T = 110 K. (For comparison, Raman data for ω A and Γ A is also shown [14]. )…”

“…superconductors) and CDW materials [3,12,13]: the photoexcited (PE) carriers first rapidly thermalize by e-e scattering (within τ e−e ≈ 10 fs) and then transfer their energy to the lattice with a characteristic electron-phonon relaxation time given by τ e−ph = k B T e / (λ ω 2 ) [12,13], where λ is the electron-phonon coupling constant, and ω 2 is the mean square phonon energy. Using ω ≈ 200 cm −1 [14] and λ ≈ 0.3 [15] we obtain (for the excitation intensities used here) τ e−ph ≈ 100 fs which is the time required for the PE carriers to relax to energies close to E F . If a gap in the DOS is present near E F , the resulting relaxation bottleneck causes carriers to accumulate in states above the gap.…”

Femtosecond Time‐ and Angle‐Resolved Photoemission as a Real‐time Probe of Cooperative Effects in Correlated Electron Materials

“…From Figure 20.5c, it is seen that this binding energy variation contains two closely spaced frequencies, which present a beating behavior with a node at 10 ps. The lower frequency of 2:45 THz has been observed by timeresolved linear reflectivity studies before [16] and is attributed to the breathing mode in the bulk of the material [17]. Due to the combined surface and bulk sensitivity of low energy photoemission, we attribute the higher frequency to a stiffer mode at the surface.…”

Evolution of coherent collective modes through consecutive charge-density-wave transitions in the(PO2)4(WO3)12

“…The appearance of new collective vibrational excitations in Raman 1-3 and coherent transient reflectivity [4][5][6] response upon charge density wave (CDW) formation is well documented [1][2][3][4][5][6][7] and theoretically quite well understood. 7 In systems with more than one CDW transition new collective modes are expected to appear below each transition temperature, as observed experimentally in the Raman response 2,3 . In the transient reflectivity response 6,8 , however, the additional coherent oscillation modes below the subsequent CDW transition temperatures have not been readily observed.…”