anharmonic coupling
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2022 ◽  
Vol 119 (3) ◽  
pp. e2113967119
Author(s):  
Laurent P. René de Cotret ◽  
Martin R. Otto ◽  
Jan-Hendrik Pöhls ◽  
Zhongzhen Luo ◽  
Mercouri G. Kanatzidis ◽  
...  

SnSe is a layered material that currently holds the record for bulk thermoelectric efficiency. The primary determinant of this high efficiency is thought to be the anomalously low thermal conductivity resulting from strong anharmonic coupling within the phonon system. Here we show that the nature of the carrier system in SnSe is also determined by strong coupling to phonons by directly visualizing polaron formation in the material. We employ ultrafast electron diffraction and diffuse scattering to track the response of phonons in both momentum and time to the photodoping of free carriers across the bandgap, observing the bimodal and anisotropic lattice distortions that drive carrier localization. Relatively large (18.7 Å), quasi-one-dimensional (1D) polarons are formed on the 300-fs timescale with smaller (4.2 Å) 3D polarons taking an order of magnitude longer (4 ps) to form. This difference appears to be a consequence of the profoundly anisotropic electron–phonon coupling in SnSe, with strong Fröhlich coupling only to zone-center polar optical phonons. These results demonstrate a high density of polarons in SnSe at optimal doping levels. Strong electron-phonon coupling is critical to the thermoelectric performance of this benchmark material and, potentially, high performance thermoelectrics more generally.


2021 ◽  
Vol 22 (21) ◽  
pp. 11926
Author(s):  
Kooknam Jeon ◽  
Myungsam Jen ◽  
Sebok Lee ◽  
Taehyung Jang ◽  
Yoonsoo Pang

The intramolecular charge transfer (ICT) of 1-aminoanthraquinone (AAQ) in the excited state strongly depends on its solvent properties, and the twisted geometry of its amino group has been recommended for the twisted ICT (TICT) state by recent theoretical works. We report the transient Raman spectra of AAQ in a dimethylsulfoxide (DMSO) solution by femtosecond stimulated Raman spectroscopy to provide clear experimental evidence for the TICT state of AAQ. The ultrafast (~110 fs) TICT dynamics of AAQ were observed from the major vibrational modes of AAQ including the νC-N + δCH and νC=O modes. The coherent oscillations in the vibrational bands of AAQ strongly coupled to the nuclear coordinate for the TICT process have been observed, which showed its anharmonic coupling to the low frequency out of the plane deformation modes. The vibrational mode of solvent DMSO, νS=O showed a decrease in intensity, especially in the hydrogen-bonded species of DMSO, which clearly shows that the solvation dynamics of DMSO, including hydrogen bonding, are crucial to understanding the reaction dynamics of AAQ with the ultrafast structural changes accompanying the TICT.


2021 ◽  
Vol 118 (25) ◽  
pp. e2104425118
Author(s):  
Li Na Quan ◽  
Yoonjae Park ◽  
Peijun Guo ◽  
Mengyu Gao ◽  
Jianbo Jin ◽  
...  

Organic–inorganic layered perovskites, or Ruddlesden–Popper perovskites, are two-dimensional quantum wells with layers of lead-halide octahedra stacked between organic ligand barriers. The combination of their dielectric confinement and ionic sublattice results in excitonic excitations with substantial binding energies that are strongly coupled to the surrounding soft, polar lattice. However, the ligand environment in layered perovskites can significantly alter their optical properties due to the complex dynamic disorder of the soft perovskite lattice. Here, we infer dynamic disorder through phonon dephasing lifetimes initiated by resonant impulsive stimulated Raman photoexcitation followed by transient absorption probing for a variety of ligand substitutions. We demonstrate that vibrational relaxation in layered perovskite formed from flexible alkyl-amines as organic barriers is fast and relatively independent of the lattice temperature. Relaxation in layered perovskites spaced by aromatic amines is slower, although still fast relative to bulk inorganic lead bromide lattices, with a rate that is temperature dependent. Using molecular dynamics simulations, we explain the fast rates of relaxation by quantifying the large anharmonic coupling of the optical modes with the ligand layers and rationalize the temperature independence due to their amorphous packing. This work provides a molecular and time-domain depiction of the relaxation of nascent optical excitations and opens opportunities to understand how they couple to the complex layered perovskite lattice, elucidating design principles for optoelectronic devices.


2021 ◽  
Author(s):  
Neil Cole-Filipiak ◽  
Robert Knepper ◽  
Mitchell A. Wood ◽  
Krupa Ramasesha

Herein, we report on the sub-picosecond to sub-nanosecond vibrational energy transfer (VET) dynamics of the solid energetic material 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) using broadband, ultrafast infrared transient absorption spectroscopy. Experiments reveal VET occurring on three distinct timescales: sub-picosecond, 5 ps, and 200 ps. The ultrafast appearance of signal at all probed modes in the mid-infrared suggests strong anharmonic coupling of all vibrations in the solid whereas the long-lived evolution demonstrates that VET is incomplete, and thus thermal equilibrium is not attained, even on the hundred picosecond timescale. Mode-selectivity of the longest dynamics suggests coupling of the N–N and axial NO<sub>2</sub> stretching modes with the long-lived, excited phonon bath.


2021 ◽  
Author(s):  
Neil Cole-Filipiak ◽  
Robert Knepper ◽  
Mitchell A. Wood ◽  
Krupa Ramasesha

Herein, we report on the sub-picosecond to sub-nanosecond vibrational energy transfer (VET) dynamics of the solid energetic material 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) using broadband, ultrafast infrared transient absorption spectroscopy. Experiments reveal VET occurring on three distinct timescales: sub-picosecond, 5 ps, and 200 ps. The ultrafast appearance of signal at all probed modes in the mid-infrared suggests strong anharmonic coupling of all vibrations in the solid whereas the long-lived evolution demonstrates that VET is incomplete, and thus thermal equilibrium is not attained, even on the hundred picosecond timescale. Mode-selectivity of the longest dynamics suggests coupling of the N–N and axial NO<sub>2</sub> stretching modes with the long-lived, excited phonon bath.


2021 ◽  
Vol 125 (9) ◽  
pp. 1910-1918
Author(s):  
Chih-Kai Lin ◽  
Qian-Rui Huang ◽  
Ying-Cheng Li ◽  
Ha-Quyen Nguyen ◽  
Jer-Lai Kuo ◽  
...  

Author(s):  
Megan F. Nielson ◽  
Brittany E. Knighton ◽  
Lauren Rawlings ◽  
Aldair Alejandro ◽  
R. Tanner Hardy ◽  
...  

2020 ◽  
Vol 1461 ◽  
pp. 012165
Author(s):  
Maxime Markov ◽  
Jelena Sjakste ◽  
Nathalie Vast ◽  
Bernard Perrin ◽  
Lorenzo Paulatto

2020 ◽  
Vol 22 (41) ◽  
pp. 24059-24069
Author(s):  
Chih-Kai Lin ◽  
Qian-Rui Huang ◽  
Jer-Lai Kuo

Fascinating Fermi resonance bands emerge from anharmonic couplings between NH stretching fundamentals and bending overtones in ammonium-centered clusters.


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