1Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.Kenta Takada 1, Kohei Yoshimi 2, Satoshi Tsutsui 3,4, Koji Kimura 5, Kouichi Hayashi 5, Ikutaro Hamada 6, Susumu Yanagisawa 7, Naotaka Kasuya 8, Shun Watanabe 8, Jun Takeya 8, and Yusuke Wakabayashi 1,9,* This study provides a robust foundation for investigating organic semiconductors and understanding the lattice dynamics of highly anisotropic motifs. Short-wavelength modes are expected to be affected by the anisotropic molecular shape, and the experimental result suggests that even the phonons having a wavelength of 140 Å are well modified, showing strong mixing of local and nonlocal phonon modes. The dispersion of low-energy optical and acoustic phonon modes, including both intermolecular and intramolecular modes, is measured along the orthorhombic principal axes. However, there are few experimental reports on phonon dispersion in organic semiconductors and no reports on modern high-mobility organic semiconductors, which hampers the complete understanding of many phenomena in organic semiconductors. Therefore, phonons are essential in organic crystals. In organic crystals, weak van der Waals interaction among the molecules increases the amplitude of the lattice vibration. ( 2011) Laut et al.The phonon dispersion of the organic semiconductor, rubrene, is experimentally measured by the inelastic x-ray scattering experiments performed at room temperature. The equations of motion employed in simulations read Couëdel et al. It was not possible, however, to explain a left-right asymmetry of opposed directions which was also present in the spectra Laut et al. If MCI is triggered in one direction, a single pattern dominates. The main conclusion was that for an appropriate orientation of the anisotropy, MCI could be triggered in two directions which leads to competing synchronization patterns. Under adequate conditions, the instability can be active only in the direction of the compression of the crystal. It was shown in simulations that the asymmetry of MCI can be caused by an anisotropy of the horizontal confinement Laut et al. ( 2014) as a possible explanation for the symmetry breaking, though it was experimentally difficult to study. A lattice deformation was suggested in Ref. Similar symmetry-breaking patterns were observed in colloids on global Reichhardt and Reichhardt ( 2004) and intermediate Bohlein and Bechinger ( 2012) scales. A synchronization pattern of alternating in-phase and anti-phase oscillations accompanied the asymmetric triggering of MCI. ( 2014), however, the instability was well pronounced dominantly in only one direction. In an ideal hexagonal lattice, the MCI is equally strong in all three main directions of the crystal, reflecting its sixfold symmetry Couëdel et al. Due to the finite vertical confinement of the crystal, the monolayer is not completely flat, allowing an out-of-plane wave mode which has an optical dispersion relation in addition to the two in-plane modes with acoustic dispersion. In ground-based experiments, the particles levitate in the plasma sheath region above the lower electrode where they can form a horizontal two-dimensional (2D) monolayer under adequate experimental conditions Chu and I ( 1994) Thomas et al.

( 2008) and self-organization Menzel et al. ( 1998), transport processes Nunomura et al. Complex plasmas are ideal model systems for phase transitions Thomas and Morfill ( 1996) Schweigert et al. ( 2005) Morfill and Ivlev ( 2009), called plasma crystals. ( 1994) Hayashi and Tachibana ( 1994).ĭue to their strong interactions with the plasma and with each other, they can form strongly coupled crystals Fortov et al. In rf discharge complex plasmas, the particles are self-trapped in the plasma Chu and I ( 1994) Thomas et al. In a laboratory radio-frequency (rf) plasma, these particles are negatively charged and thus repel each other. Complex or dusty plasmas are weakly ionized gases containing micron-size particles.

Phonon dispersio dash vertical