scholarly journals Phonon Spectra of Small Colloidal II-VI Semiconductor Nanocrystals

2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
Volodymyr Dzhagan ◽  
Mykhailo Valakh ◽  
Nikolai Mel'nik ◽  
Olexandra Rayevska ◽  
Irina Lokteva ◽  
...  
Keyword(s):  
Semiconductor Nanocrystals ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Phonon Coupling ◽  
Phonon Modes ◽  
Phonon Spectra ◽  
Electron Phonon Coupling ◽  
Unified View ◽  
Resonant Raman ◽  
Broad Feature

Resonant Raman spectroscopy has been employed to explore the first- and higher-order phonon spectra of several kinds of II-VI nanocrystals (NCs), with the aim of better understanding of the nature of phonon modes and forming a unified view onto the vibrational spectrum of semiconductor NCs. Particularly, besides the previously discussed TO, SO, LO, and 2LO modes, the combinational modes of TO+LO and SO+LO can be assumed to account for the lineshape of the spectrum below 2LO band. No trace of 2TO or 2SO band was detected, what can be the result of the dominance of Fröhlich mechanism in electron-phonon coupling in II-VI compounds. The resonant phonon Raman spectrum of NCs smaller than 2 nm is shown to be dominated by a broad feature similar to the SO mode of larger NCs or phonon density of states of a bulk crystal.

scholarly journals Resonance and antiresonance in Raman scattering in GaSe and InSe crystals

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. Osiekowicz ◽  
D. Staszczuk ◽  
K. Olkowska-Pucko ◽  
Ł. Kipczak ◽  
M. Grzeszczyk ◽  
...  
Keyword(s):  
Raman Scattering ◽  
Temperature Effect ◽  
Band Gap ◽  
Raman Spectra ◽  
Quantum Interference ◽  
Optical Band Gap ◽  
Phonon Coupling ◽  
Phonon Modes ◽  
Electron Phonon Coupling ◽  
Resonant Raman

AbstractThe temperature effect on the Raman scattering efficiency is investigated in $$\varepsilon$$ ε -GaSe and $$\gamma$$ γ -InSe crystals. We found that varying the temperature over a broad range from 5 to 350 K permits to achieve both the resonant conditions and the antiresonance behaviour in Raman scattering of the studied materials. The resonant conditions of Raman scattering are observed at about 270 K under the 1.96 eV excitation for GaSe due to the energy proximity of the optical band gap. In the case of InSe, the resonant Raman spectra are apparent at about 50 and 270 K under correspondingly the 2.41 eV and 2.54 eV excitations as a result of the energy proximity of the so-called B transition. Interestingly, the observed resonances for both materials are followed by an antiresonance behaviour noticeable at higher temperatures than the detected resonances. The significant variations of phonon-modes intensities can be explained in terms of electron-phonon coupling and quantum interference of contributions from different points of the Brillouin zone.

THERMODYNAMIC CHARACTERISTICS OF Y–Ba–Cu–O TYPE COMPOUNDS IN THE MODEL OF STRONG ELECTRON–PHONON COUPLING

1988 ◽  
Vol 02 (05) ◽  
pp. 837-845 ◽  
Author(s):  
A. A. Golubov
Keyword(s):  
Numerical Solutions ◽  
Low Frequency ◽  
Thermodynamic Characteristics ◽  
Coupling Model ◽  
Phonon Coupling ◽  
Eliashberg Equations ◽  
Phonon Modes ◽  
Strong Electron ◽  
Phonon Spectra ◽  
Electron Phonon Coupling

Based on recently measured phonon density of states of Y–Ba–Cu–O an investigation of the strong electron-phonon coupling model is carried out. The numerical solutions of the real axis Eliashberg equations are obtained for a number of phonon spectra parameters. Isotope shifts of T c , spectral behavior of the pairing energy Δ(ω) and the ratio 2Δ g / T c (where Δ g is the gap edge) are calculated. The model gives a very small oxygen isotope shift for rather moderate values of the electron-phonon coupling constant λ ~ 3. The results strongly suggest the weak coupling with high frequency phonon modes and strong coupling with low frequency modes.

Anharmonic phonon–electron effects on phonon density of states in La2−xSrxCuO4

2015 ◽  
Vol 29 (29) ◽  
pp. 1550177 ◽  
Author(s):  
Vinod Ashokan ◽  
B. D. Indu
Keyword(s):  
Density Of States ◽  
Inelastic Neutron Scattering ◽  
Inelastic Neutron ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Phonon Coupling ◽  
Perturbative Approach ◽  
Electron Phonon Coupling ◽  
Double Time ◽  
Electron Effects

In the present work, the phonon density of states (PDOS) for [Formula: see text] crystal is investigated by using the double time thermodynamic Green’s function method via a non-perturbative approach. A newly formulated Hamiltonian is considered for the lattice dynamics of phonon, which includes the effects of electron–phonon interactions, lattice anharmonicities and the interacting isotopic impurities. The automated emergence of pairons and [Formula: see text] wave pairing mechanism appears as a salient features of the theory. The PDOS is found to be dependent on temperature, impurity concentration, electron–phonon coupling coefficient and renormalized frequencies, and the numerical investigations on PDOS exhibits fairly good agreements with the inelastic neutron scattering experimental observations.

scholarly journals Evidence for superconductivity in Li-decorated monolayer graphene

2015 ◽  
Vol 112 (38) ◽  
pp. 11795-11799 ◽  
Author(s):  
B. M. Ludbrook ◽  
G. Levy ◽  
P. Nigge ◽  
M. Zonno ◽  
M. Schneider ◽  
...  
Keyword(s):  
Low Temperature ◽  
Photoemission Spectroscopy ◽  
Monolayer Graphene ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Phonon Coupling ◽  
Temperature Dependent ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Electron Phonon Coupling ◽  
First Time

Monolayer graphene exhibits many spectacular electronic properties, with superconductivity being arguably the most notable exception. It was theoretically proposed that superconductivity might be induced by enhancing the electron–phonon coupling through the decoration of graphene with an alkali adatom superlattice [Profeta G, Calandra M, Mauri F (2012) Nat Phys 8(2):131–134]. Although experiments have shown an adatom-induced enhancement of the electron–phonon coupling, superconductivity has never been observed. Using angle-resolved photoemission spectroscopy (ARPES), we show that lithium deposited on graphene at low temperature strongly modifies the phonon density of states, leading to an enhancement of the electron–phonon coupling of up to λ≃0.58. On part of the graphene-derived π∗-band Fermi surface, we then observe the opening of a Δ≃0.9-meV temperature-dependent pairing gap. This result suggests for the first time, to our knowledge, that Li-decorated monolayer graphene is indeed superconducting, with Tc≃5.9 K.

scholarly journals Acoustic phonon lifetimes limit thermal transport in methylammonium lead iodide

2018 ◽  
Vol 115 (47) ◽  
pp. 11905-11910 ◽  
Author(s):  
Aryeh Gold-Parker ◽  
Peter M. Gehring ◽  
Jonathan M. Skelton ◽  
Ian C. Smith ◽  
Dan Parshall ◽  
...  
Keyword(s):  
Lattice Dynamics ◽  
Acoustic Phonon ◽  
Optoelectronic Devices ◽  
High Energy ◽  
High Energy Resolution ◽  
Phonon Coupling ◽  
Lead Iodide ◽  
Phonon Modes ◽  
Electron Phonon Coupling ◽  
Methylammonium Lead Iodide

Hybrid organic–inorganic perovskites (HOIPs) have become an important class of semiconductors for solar cells and other optoelectronic applications. Electron–phonon coupling plays a critical role in all optoelectronic devices, and although the lattice dynamics and phonon frequencies of HOIPs have been well studied, little attention has been given to phonon lifetimes. We report high-precision momentum-resolved measurements of acoustic phonon lifetimes in the hybrid perovskite methylammonium lead iodide (MAPI), using inelastic neutron spectroscopy to provide high-energy resolution and fully deuterated single crystals to reduce incoherent scattering from hydrogen. Our measurements reveal extremely short lifetimes on the order of picoseconds, corresponding to nanometer mean free paths and demonstrating that acoustic phonons are unable to dissipate heat efficiently. Lattice-dynamics calculations using ab initio third-order perturbation theory indicate that the short lifetimes stem from strong three-phonon interactions and a high density of low-energy optical phonon modes related to the degrees of freedom of the organic cation. Such short lifetimes have significant implications for electron–phonon coupling in MAPI and other HOIPs, with direct impacts on optoelectronic devices both in the cooling of hot carriers and in the transport and recombination of band edge carriers. These findings illustrate a fundamental difference between HOIPs and conventional photovoltaic semiconductors and demonstrate the importance of understanding lattice dynamics in the effort to develop metal halide perovskite optoelectronic devices.

scholarly journals Ultrafast electron calorimetry uncovers a new long-lived metastable state in 1T-TaSe2 mediated by mode-selective electron-phonon coupling

2019 ◽  
Vol 5 (3) ◽  
pp. eaav4449 ◽  
Author(s):  
Xun Shi ◽  
Wenjing You ◽  
Yingchao Zhang ◽  
Zhensheng Tao ◽  
Peter M. Oppeneer ◽  
...  
Keyword(s):  
Heat Capacity ◽  
Metastable State ◽  
Density Wave ◽  
Charge Order ◽  
Phonon Coupling ◽  
Phonon Modes ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Quantum Matter ◽  
Electron Phonon Coupling ◽  
Equilibrium Phases

Quantum materials represent one of the most promising frontiers in the quest for faster, lightweight, energy-efficient technologies. However, their inherent complexity and rich phase landscape make them challenging to understand or manipulate. Here, we present a new ultrafast electron calorimetry technique that can systematically uncover new phases of quantum matter. Using time- and angle-resolved photoemission spectroscopy, we measure the dynamic electron temperature, band structure, and heat capacity. This approach allows us to uncover a new long-lived metastable state in the charge density wave material 1T-TaSe2, which is distinct from all the known equilibrium phases: It is characterized by a substantially reduced effective total heat capacity that is only 30% of the normal value, because of selective electron-phonon coupling to a subset of phonon modes. As a result, less energy is required to melt the charge order and transform the state of the material than under thermal equilibrium conditions.

Resonant Raman technique-a powerful tool for exploring electron-phonon coupling in Se nanoclusters

2006 ◽  
Author(s):  
Irene Ling Li ◽  
Jian Pang Zhai ◽  
Zi Kang Tang ◽  
Shuang Chen Ruan ◽  
Min Zhang
Keyword(s):  
Phonon Coupling ◽  
Electron Phonon Coupling ◽  
Resonant Raman

One-Phonon Spectra and Effective Phonon Density-of-States in CaGa2S4

2000 ◽  
Vol 39 (S1) ◽  
pp. 307 ◽  
Author(s):  
Nazim Mamedov ◽  
Seishi Iida ◽  
Tamao Aoki-Matsumoto ◽  
Ariyuki Kato ◽  
Makoto Yamazaki ◽  
...  
Keyword(s):  
Density Of States ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Phonon Spectra
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