The influence of temperature and pressure on the optical spectrum of monoclinic tetrathiafulvalene crystals

1985 ◽  
Vol 63 (8) ◽  
pp. 1088-1091
Author(s):  
Pierre Baillargeon ◽  
Larbi Roubi ◽  
Cosmo Carlone ◽  
Kim Doan Truong
Keyword(s):  
Optical Spectrum ◽  
Leading Edge ◽  
Low Energy ◽  
Phonon Interaction ◽  
Influence Of Temperature ◽  
Electron Phonon Interaction ◽  
Volume Dilatation ◽  
Total Temperature ◽  
Two Temperatures ◽  
Temperature And Pressure

The absorption spectrum of monoclinic tetrathiafulvalene has been obtained from 15 400 to 28 600 cm−1 at 0 bar for two temperatures: 84 and 298 K. The change with temperature of the low-energy leading edge (the Ag → Bu transition) is −1.0 ± 0.5 cm−1∙K−1. The spectrum was also obtained at 298 K as a function of pressure up to 6.6 × 104 bar. The change with pressure is −40 ± 5 cm−1∙103 bar−1. The total temperature dependence consists of the extrinsic contribution, which is a measure of the electron–phonon interaction and which we estimate to be −2.2 cm−1∙K−1, and the intrinsic contribution, which is a measure of the volume dilatation and which we estimate to be + 1.2 cm−1∙K−1.

Photoluminescence spectrum of tetracyanoquinodimethane crystals at 25 K: temperature and pressure dependence

1986 ◽  
Vol 64 (3) ◽  
pp. 277-281
Author(s):  
S. Desgreniers ◽  
L. Roubi ◽  
C. Carlone ◽  
H. D. Hochheimer
Keyword(s):  
Photoluminescence Spectrum ◽  
Anion Radical ◽  
Temperature Shift ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Stretching Vibration ◽  
Total Temperature ◽  
Temperature And Pressure ◽  
Low Pressures ◽  
Interaction Contribution

Using 488.0 and 514.5 nm laser radiation, we have obtained the luminescence spectrum of excited tetracyanoquinodimethane (TCNQ) crystals from 10 to 36 K at a pressure of 0 GPa. At 10 K, the luminescent peaks occur at 14 100, 15 000, 15 700 (±100), 16 300, 16 600, 16 800, and 17 200 (±50) cm−1. The temperature shift of the spectrum is −16 ± 7 cm−1∙K−1. At a constant temperature of 25 K, we followed the luminescent peaks as a function of pressure up to 8.5 GPa. The pressure shift of the luminescence, at low pressures, is −100 ± 50 cm−1∙GPa−1. We estimate that the volume-dilation contribution to the total temperature dependence is at most +2 cm−1∙K−1, in which case the electron–phonon-interaction contribution is −18 cm−1∙K−1. We have also examined the Raman spectrum at 25 K and have found the 1389 cm−1 ν4 (C=C) wing-stretching vibration of TCNQ−; its pressure behaviour is similar to that observed in TCNQ salts. The measurements were made on crystals grown very differently in two separate laboratories, and the effects induced by temperature or pressure were reversible. We attribute the luminescence to the 2B2g → 2B1μ transition of the TCNQ− anion radical, whose presence is due to impurities having a concentration of less than 0.01%.

Temperature and pressure dependence of the electronic structure of tetracyanoquinodimethane crystals and the effect of impurities

1985 ◽  
Vol 63 (12) ◽  
pp. 1513-1517 ◽  
Author(s):  
L. Roubi ◽  
C. Cyr ◽  
S. Desgreniers ◽  
C. Carlone ◽  
K. D. Truong ◽  
...  
Keyword(s):  
Pressure Dependence ◽  
Room Temperature ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
First Case ◽  
Volume Dilatation ◽  
Structural Differences ◽  
Irreversible Effects ◽  
Effect Of Impurities ◽  
Temperature And Pressure

The absorption spectrum (12 500–32 260 cm−1) of tetracyanoquinodimethane crystals has been obtained at 0 bars in the [001] and [010] direction at 84 and 300 K. The peak of the Ag → Bu transition has been identified at 21 370 cm−1 and that of the Ag → Au transition at 22 000 cm−1. The change with temperature of both transitions was −3.4 ± 0.1 cm−1∙K−1. The [001] absorption was also obtained at room temperature as a function of the pressure, up to 5.0 × 104 bar, for crystals grown in two different laboratories, giving the change with pressure as −0.037 ± 0.003 and −0.092 ± 0.010 cm−1∙bar−1, respectively. At ambient temperature the explicit contribution, which is a measure of the electron–phonon interaction, was negative and dominated the temperature dependence. The implicit contribution, which is a measure of the volume dilatation, contributed in the opposite way, i.e., positively. Working at room temperature, we observed on both samples irreversible effects at higher pressures. In the first case, a discontinuous change occurred at (12 ± 1) × 103 bar, with new peaks appearing both at higher energy (25 600 cm−1) and lower energy (12 500 cm−1). In the second case, the absorption peak shifted continuously towards lower energies, but it broadened abruptly above 1.3 × 104 bar. We believe that the differences in the pressure dependence of the optical properties are due to the presence of small amounts of impurities in the samples causing subtle structural differences and that the irreversible effects are due to pressure-induced chemical changes.

ROLE OF THE ELECTRON–PHONON INTERACTION ON THE SPECTRAL DENSITY AND PSEUDOGAP IN CUPRATES

2002 ◽  
Vol 16 (23) ◽  
pp. 3465-3471
Author(s):  
I. CHAUDHURI ◽  
S. K. GHATAK
Keyword(s):  
Critical Temperature ◽  
Spectral Density ◽  
Low Energy ◽  
Phonon Interaction ◽  
Energy Excitation ◽  
Electron Phonon Interaction ◽  
Peak Structure ◽  
Electronic Model ◽  
Jahn Teller

The pseudogap structure in low energy excitation in cuprates appears below a temperature and the spectral density exhibits strong wave-vector dependence. An electronic model that emphasized the coupling of carrier in Cu-O with phonon is examined for pseudogap. The electron–phonon interaction originates from the modulation of on-site and hopping energy and leads to spontaneous Jahn–Teller-like distortion and pseudogap below a critical temperature. At low temperature the spectral density has two-peak structure about the Fermi level for all k along Γ-M whereas such structure exists along Γ-X for small k only. The magnitude of pseudogap shows strong k-dependence — maximum along Γ-M and vanishes along Γ-X. These features emphasize the role of electron–phonon interaction in formation of pseudogap.

The simulation of the electron-phonon interaction in silicon

2018 ◽  
Vol 30 (12) ◽  
pp. 3-16
Author(s):  
A. Berezin ◽  
◽  
Yu. Volkov ◽  
M. Markov ◽  
I. Tarakanov ◽  
...  
Keyword(s):  
Phonon Interaction ◽  
Electron Phonon Interaction
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