scholarly journals Coherence lifetime broadened optical transitions in a 2 atom diameter HgTe nanowire: a temperature dependent resonance Raman study

RSC Advances ◽  
2016 ◽  
Vol 6 (98) ◽  
pp. 95387-95395 ◽  
Author(s):  
Joseph H. Spencer ◽  
David C. Smith ◽  
Liam P. McDonnell ◽  
Jeremy Sloan ◽  
Reza J. Kashtiban
Keyword(s):  
Raman Scattering ◽  
Temperature Dependence ◽  
Resonance Raman ◽  
Strong Temperature Dependence ◽  
Optical Transitions ◽  
Temperature Dependent ◽  
Raman Study ◽  
Electronic Coherence ◽  
Excitonic Effects

The paper sets out the role of electronic coherence in the strong temperature dependence of the intensity of Raman scattering from two atom diameter HgTe nanowires. It argues the behavior is likely common in extreme nanowires, and possibly due to excitonic effects.

scholarly journals Disentangling Dynamical Quantum Coherences in the Fenna-Matthews-Olson Complex

2021 ◽  
Author(s):  
Hong-Guang Duan ◽  
Ajay Jha ◽  
Lipeng Chen ◽  
Vandana Tiwari ◽  
Richard Cogdell ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Reaction Center ◽  
Low Temperatures ◽  
Quantum Coherence ◽  
Energy Transport ◽  
Light Harvesting ◽  
Quantum Decoherence ◽  
Strong Temperature Dependence ◽  
Temperature Dependent ◽  
Electronic Coherence

Abstract In the primary step of natural light-harvesting, the energy of a solar photon is captured in antenna chlorophyll as a photoexcited electron-hole pair, or an exciton. Its efficient conversion to stored chemical potential occurs in the special pair reaction center, which has to be reached by down-hill ultrafast excited state energy transport. Key to this process is the degree of interaction between the chlorophyll chromophores that can lead to spatial delocalization and quantum coherence effects. The importance of quantum contributions to energy transport depends on the relative coupling between the chlorophylls in relation to the intensity of the fluctuations and reorganization dynamics of the surrounding protein matrix, or bath. The latter induce uncorrelated modulations of the site energies, resulting in quantum decoherence, and localization of the spatial extent of the exciton. The current consensus is that under physiological conditions quantum decoherence occurs on the 10 fs time scale, and quantum coherence plays little role for the observed picosecond energy transfer dynamics. In this work, we reaffirm this from a different point of view by finding that the true onset of important electronic quantum coherence only occurs at extremely low temperatures of ~20 K. We have directly determined the exciton coherence times using two-dimensional (2D) electronic spectroscopy of the Fenna-Matthew-Olson (FMO) complex over an extensive temperature range. At 20 K, we show that electronic coherences persist out to 200 fs (close to the antenna) and marginally up to 500 fs at the reaction-center side. The electronic coherence is found to decay markedly faster with modest increases in temperature to become irrelevant above 150 K. This temperature dependence also allows disentangling the previously reported long-lived beatings thought to be evidence for electronic quantum coherence contributions. We show that they result from mixing vibrational coherences in the electronic ground state. We also uncover the relevant electronic coherence between excited electronic states and examine the temperature-dependent non-Markovianity of the transfer dynamics to show that the bath involves uncorrelated motions even to low temperatures. The observed temperature dependence allows a clear separation of the fragile electronic coherence from the robust vibrational coherence. The specific details of the critical bath interaction are treated through a theoretical model based on measured bath parameters that reproduces the temperature dependent dynamics. By this, we provide a complete picture of the bath interaction which places these systems in the regime of strong bath coupling. We believe this main conclusion to be generically valid for light harvesting systems. This principle makes the systems robust against otherwise fragile quantum effects as evidenced by the strong temperature dependence. We conclude that nature explicitly exploits decoherence or dissipation in engineering site energies to yield downhill energy gradients to unerringly direct energy, even on the fastest time scales of biological processes.

A density functional theory and resonance Raman study of a benzotriazole dye used in surface enhanced resonance Raman scattering

2006 ◽  
Vol 789 (1-3) ◽  
pp. 59-70 ◽  
Author(s):  
Prokopis C. Andrikopoulos ◽  
Karen M. McCarney ◽  
David R. Armstrong ◽  
Rachael E. Littleford ◽  
Duncan Graham ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Raman Scattering ◽  
Density Functional ◽  
Resonance Raman ◽  
Resonance Raman Scattering ◽  
Functional Theory ◽  
Surface Enhanced ◽  
Raman Study

STUDY OF MOLECULAR MOTIONS IN TWO LIQUID CRYSTAL FORMING COMPOUNDS EMPLOYING PLS

2006 ◽  
Vol 20 (14) ◽  
pp. 2019-2034 ◽  
Author(s):  
K. CHANDRAMANI SINGH ◽  
M. SHARMA ◽  
P. C. JAIN
Keyword(s):  
Liquid Crystal ◽  
Temperature Dependence ◽  
Liquid Crystalline ◽  
Positron Lifetime ◽  
Strong Temperature Dependence ◽  
Molecular Motions ◽  
Temperature Dependent ◽  
Slow Cooling ◽  
Positron Lifetime Spectroscopy ◽  
Motion Studies

Results of molecular motion studies carried out in two liquid crystal forming compounds n-p-cyano-p-hexyloxybiphenyl (M18) and n-p-ethoxybenzylidene-p-butylaniline (EBBA) using positron lifetime spectroscopy (PLS) are presented. Temperature dependent positron lifetime measurements have been performed in each compound during the heating cycle of samples prepared by either quenching or slow cooling from the respective liquid crystalline phase of the compounds. In both the compounds, behaviors of the quenched and slow cooled samples are found to be different. The material in the quenched sample, unlike the slow-cooled sample, exhibits strong temperature dependence before it undergoes a glass transition. In each case, the temperature dependence of o-Ps pick-off lifetime in the quenched sample shows broad peaks at various characteristic temperatures. These peaks have been attributed to various intra- and inter-molecular motions associated with these compounds. The characteristic frequencies of some of the modes observed in the present work agree well with the literature reported values obtained from FIR and Raman studies. The present study demonstrates the usefulness of PLS in the study of molecular motions.

A resonance Raman study of the temperature dependence of ligand photolysis and recombination in hemoglobins

1984 ◽  
Vol 112 (4) ◽  
pp. 351-355 ◽  
Author(s):  
M.R. Ondrias ◽  
T.W. Scott ◽  
J.M. Friedman ◽  
V.W. Macdonald
Keyword(s):  
Temperature Dependence ◽  
Resonance Raman ◽  
Raman Study

scholarly journals Temperature-Dependent Evolution of Raman Spectra of Methylammonium Lead Halide Perovskites, CH3NH3PbX3 (X = I, Br)

Molecules ◽  
2019 ◽  
Vol 24 (3) ◽  
pp. 626 ◽  
Author(s):  
Kousuke Nakada ◽  
Yuki Matsumoto ◽  
Yukihiro Shimoi ◽  
Koji Yamada ◽  
Yukio Furukawa
Keyword(s):  
Phase Transitions ◽  
Temperature Dependence ◽  
Temperature Dependent ◽  
High Power Conversion Efficiency ◽  
Perovskite Materials ◽  
Hybrid Perovskite ◽  
Temperature Ranges ◽  
Raman Study ◽  
Halide Perovskites ◽  
Motional Narrowing

We present a Raman study on the phase transitions of organic/inorganic hybrid perovskite materials, CH3NH3PbX3 (X = I, Br), which are used as solar cells with high power conversion efficiency. The temperature dependence of the Raman bands of CH3NH3PbX3 (X = I, Br) was measured in the temperature ranges of 290 to 100 K for CH3NH3PbBr3 and 340 to 110 K for CH3NH3PbI3. Broad ν1 bands at ~326 cm−1 for MAPbBr3 and at ~240 cm−1 for MAPbI3 were assigned to the MA–PbX3 cage vibrations. These bands exhibited anomalous temperature dependence, which was attributable to motional narrowing originating from fast changes between the orientational states of CH3NH3+ in the cage. Phase transitions were characterized by changes in the bandwidths and peak positions of the MA–cage vibration and some bands associated with the NH3+ group.

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