Anomalous Nanoscale Optoacoustic Phonon Mixing in Nematic Mesogens

Dima Bolmatov, Dmytro Soloviov, Dmitry Zav'Yalov, Lewis Sharpnack, Deña M. Agra-Kooijman, Satyendra Kumar, Jiawei Zhang, Mengkun Liu, John Katsaras

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

Abstract

Recent inelastic X-ray scattering (IXS) experiments on mesogens have revealed entirely new capabilities with regards to their nanoscale phonon-assisted heat management. Mesogens such as nematic liquid crystals (LCs) are appealing systems for study because their structure and morphology can easily be tuned. We report on Q-resolved ultra-high-resolution IXS, X-ray diffraction, and THz time-domain spectroscopy experiments combined with large-scale all-atom molecular dynamics simulations on the dynamic properties of 5CB LCs. For the first time, we observe a strong mixing of phonon excitations originating from independent in-phase and out-of-phase van-der-Waals-mediated displacement patterns. The coexistence of transverse acoustic and optical modes of 5CB LCs at near room temperature is revealed through the emergent transverse phonon gap and THz light-phonon coupling taking place within the same energy range. Furthermore, our experimental observations are supported by analysis showing correlations of spontaneous fluctuations of LCs on picosecond time scales. These findings are significant for the design of a new generation of soft molecular vibration-sensitive nanoacoustic and optomechanical applications.

Original languageEnglish
Pages (from-to)2546-2553
Number of pages8
JournalJournal of Physical Chemistry Letters
Volume9
Issue number10
DOIs
StatePublished - May 17 2018

Funding

We thank Larry Carr, Alexey Suvorov, Yong Q. Cai, Mikhail Zhernenkov, Takeshi Egami, and Dmitry Bedrov for fruitful discussions. We acknowledge Xinzhong Chen for his assistance carrying out THz TDS measurements. The work at the National Synchrotron Light Source-II, Brookhaven National Laboratory, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under contract no. DE-SC0012704. We thank Alexey Suvorov, Yong Q. Cai, and Mikhail Zhernenkov for their assistance to carry out IXS measurements at 10-ID beamline, NSLS II. J.K. is supported through the Scientific User Facilities Division of the U.S. Department of Energy (DOE), Office of Basic Energy Sciences (BES), managed by UT-Battelle under contract no. DE-AC05 00OR2275.

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