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Emergent Optical Phononic Modes upon Nanoscale Mesogenic Phase Transitions
Dima Bolmatov1, Mikhail Zhernenkov1, Lewis Sharpnack2
1National Synchrotron Light Source II, Brookhaven National Laboratory , Upton, New York 11973, United States.
Nano Letters
|May 27, 2017
Summary
Inelastic X-ray scattering reveals terahertz phononic excitations in liquid crystals across different phases. These collective excitations can be tuned, offering new ways to control soft metamaterial properties for energy applications.
Area of Science:
- Soft matter physics
- Condensed matter physics
- Materials science
Background:
- Investigating molecular-scale phononic excitations in soft matter is experimentally challenging due to limitations in resolving low-energy modes.
- Advances in inelastic X-ray scattering (IXS) now allow high-resolution studies of these low-energy collective motions.
- Understanding phononic behavior in mesogenic systems is crucial for developing energy management strategies through structural control.
Purpose of the Study:
- To investigate the persistence and behavior of terahertz phononic excitations in different phases of a liquid crystal (D7AOB) using high-contrast IXS.
- To explore the potential for manipulating collective excitations at the nanoscale for optomechanical applications.
Main Methods:
- High-contrast inelastic X-ray scattering (IXS) measurements were performed on a liquid crystal sample (D7AOB).
- Analysis focused on the Q-dependence of collective mode behavior and the identification of longitudinal and transverse phononic modes.
Main Results:
- Terahertz phononic excitations were observed to persist across the crystal, smectic A, and isotropic phases of D7AOB.
- The smectic A phase uniquely supports a van der Waals-mediated nonhydrodynamic mode with optical-like phononic characteristics.
- These collective excitations demonstrate tunability at nanometer-terahertz scales by altering the mesogenic phase.
Conclusions:
- The study demonstrates the presence and tunability of terahertz phononic excitations in liquid crystals, offering new insights into soft matter dynamics.
- The findings highlight the potential for manipulating optomechanical properties of soft metamaterials by controlling mesogenic phase and collective excitations.
- This research paves the way for energy-inspired innovations leveraging controlled soft matter structures.
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