"Stable localized structures in one and two spatial dimensions: a review and a perspective"
Prof. Helmut R. Brand

Aug 19, 2013

講演題目：　 Stable localized structures in one and two spatial dimensions: a review and a perspective
講　師　：　Prof. Helmut R. Brand
　　　　　Technische Universitat Braunschweig, Institute for Condensed Matter Physics, 38106 Braunschweig, Germany
日　時　：　平成25年8月19日 (木) 13:00-14:00
場　所　：　北海道大学理学部２号館211室（2-2-11）

要　旨　：
We give an overview over stable localized solutions in nonlinear driven non-equilibrium systems, often denoted as dissipative solitons [1]. We cover different mechanisms to generate stable localized structures in various types of prototype equations, namely, envelope equations, order parameter equations and phase equations.For envelope equations nonvariational effects are a key ingredient as emphasized first by Thual and Fauve [2]. This mechanism turns out to be very robust and allows for many different stable particle- and hole-like solutions in one and two spatial dimensions. The interaction of localized solutions can give rise to many different types of outcomes including propagating holes as a result of a collision of propagating particles of fixed shape [3]. For order parameter equations a trapping mechanism can generate localized solutions of arbitrary lengths [4]. A third type of localized solutions involves nonlinear phase dynamics giving rise to stable localized patterns in the wavelength for a nonlinear phase equation [5] or in coupled envelope and phase equations [6]. We also cover briefly recent work on the effects of noise on localized solutions in envelope equations [7,8] and close with an overview of possible applications to systems as diverse as surface reactions under UHV conditions [9], binary fluid convection [10] or holes observed in corn and potato starch suspensions [11].

[1] N. Akhmediev and A. Ankiewicz, Eds., Dissipative Solitons, Springer, Heidelberg (2005).
[2] O. Thual and S. Fauve, J.Phys. France 49, 1829 (1988).
[3] O. Descalzi, J. Cisternas, and H.R. Brand, Phys. Rev. E 74, 065201 (2006).
[4] H. Sakaguchi and H.R. Brand, Physica D 97, 274 (1996).
[5] H.R. Brand and R.J. Deissler, Phys. Rev. Lett. 63, 508 (1989).
[6] H. Sakaguchi, Prog. Theor. Phys. 87, 1049 (1992).
[7] O. Descalzi, J. Cisternas, D. Escaff, and H.R. Brand, Phys. Rev. Lett. 102, 188302 (2009).
[8] C. Cartes, J. Cisternas, O. Descalzi, and H.R. Brand, Phys. Rev. Lett. 109, 178303 (2012).
[9] H.H. Rotermund, S. Jakubith, A. von Oertzen, and G. Ertl, Phys. Rev. Lett. 66, 3083 (1991).
[10] P. Kolodner, Phys. Rev. A 44, 6448 (1991); Phys. Rev. A 44, 6466 (1991).
[11] H. Ebata and M. Sano, Phys. Rev. Lett. 107, 088301 (2011).

世話人　 北　孝文
(kita@phys.sci.hokudai.ac.jp)
北海道大学大学院理学研究院物理学部門

"Real-time observations of the quasi-particle relaxation dynamics in various complex systems by means of femtosecond laser spectroscopy "
Ljupka Stojcevska

Jul 22, 2013

講演題目：　 Real-time observations of the quasi-particle relaxation dynamics in various complex systems by means of femtosecond laser spectroscopy
講　師　：　Ljupka Stojcevska
　　　　　Complex Matter Department, Jozef Stefan Institute, Slovenia
日　時　：　平成25年7月22日 16:30-
場　所　：　北海道大学 工学部大会議室(A1-17)

要　旨　：
We have performed systematic study of the quasiparticle relaxation dynamics in various complex systems such as cuprates, iron-based pnictides superconductors and charge-density wave systems. In undoped iron-based pnictides, exhibiting a spin-density wave (SDW) ordering, we observe a bottleneck associated with a partial charge-gap opening. Similarly as in the previous reported studies, a single relaxation process is observed, showing a remarkable critical slowing down of the quasiparticle (QP) relaxation dynamics at the SDW transition temperature. On the other hand, in the optimally doped crystals, a multiple relaxation processes are present with distinct SC-state quasiparticle recombination dynamics exhibiting a BCS-like T-dependent superconducting gap, and a pseudogap (PG)-like feature at higher temperatures. In all optimally doped cuprates and iron-based pnictides, we observe a saturation of the superconducting relaxation component. By taking into account the optical constants such as penetration depth and reflectivity we can accurately calculate energy needed for destruction of the superconducting state. If we compare the magnitudes of the destruction and cond ensation energies we notice a significant discrepancy in cuprates and iron-based pnictides, which can be explained with a phonon-mediated QP bottleneck mechanism. In contrast, in the charge-density wave systems, the destruction is faster and electronic; therefore it can not be explained in the frame of the proposed QP bottleneck mechanism. The second moment of the Eliashberg function, obtained from the relaxation rate in the metallic state at higher temperatures, has similar values in different iron-based pnictides, which indicates a moderate electron phonon coupling. More recently we have observed a switching between an equilibrium state to a metastable in 1T-TaS2 charge-density wave system by means of ultrafast laser quench through a symmetry breaking transition. The switching is repeatable and accompanied with a change in reflectivity and DC resistance, opening a new possibility for ultrafast non-volatile memory devices.

世話人　 戸田 泰則
(toda@eng.hokudai.ac.jp)
北海道大学大学院工学研究院応用物理学部門

"Sliding charge-density-wave in two-dimensional rare-earth tellurides"
Prof. Pierre Monceau

Mar 21, 2013

応用物理学部門学術講演会、杉野目記念会海外学識者講演会、第188回エ ンレイソウの会共催
講演題目：　Sliding charge-density-wave in two-dimensional rare-earth tellurides
講　師　：　Prof. Pierre Monceau
　　　　　Institut Neel, CNRS and University Joseph Fourier, France
日　時　：　平成25年3月21日（木） 15:00-16:30
場　所　：　北海道大学 工学部大会議室(A1-17)

要　旨　：
Amplitude charge density wave (CDW) excitations in rare earth tritellurides (RTe3) were probed by Raman scattering and femtosecond pump-probe spectroscopy. However, collective charge phase excitations could not be observed in far-infrared measurements due to screening by the residual metallic component at the Fermi surface. But the phase collective mode is accessible through nonlinear transport properties. We report such nonlinear transport properties in the layered DyTe3 at temperatures below the CDW phase transition, TP = 302K. Conductivity is increasing sharply above a threshold field. Under application of a rf field Shapiro steps are clearly observed. These features demonstrate for the first time CDW sliding in two-dimensional compounds. In collaboration with A. A. Sinchenko (Kotel’nikov Institut, Moscow) and P. Lejay (Institut Neel, Grenoble).

世話人　 丹田　聡
(tanda@eng.hokudai.ac.jp)
北海道大学大学院工学研究院応用物理学部門

"Electronic ferroelectricity in carbon-based systems: from reality of organic conductors to promises of polymers"
Prof. Dr. Natasha Kirova

Jan 21, 2013

日本物理学会北海道支部講演会 共催: 第185回エンレイソウの会共催
講演題目：　Local and non-equilibrium processes in charge density waves
講　師　：　Prof. Dr. Natasha Kirova
　　　　　CNRS, University Paris-Sud, France
日　時　：　平成25年1月21日（月） 13:30-16:30
場　所　：　北海道大学 工学部大会議室(A1-17)

要　旨　：
Ferroelectricity is a demanded effect in fundamental and applied solid state physics. Till now, the ferroelectrics were available mostly in electronically and optically inert, usually inorganic, materials. The electronic ferroelectricity was discovered in conducting organic stacks of (TMTTF)2X at their Mott insulator phase, and now it is studied in layered BEDT-compounds with the charge ordering, and in complexes with neutral-ionic transitions; this research is very active in Japan. In this talk we discuss the existing and the expected ferroelectricity in electronically and optically active carbon-based materials: organic crystals, conducting polymers and even graphene ribbons. We indicate the type of conducting polymers ? the substituted polyacetylene - where the ferroelectricity should be present. The theory predicted an existence of solitons with non-integer variable charges, both with and without spin, which are the walls separating domains with opposite electric polarisation. Their physics will serve to relate transient ferroelectric processes and the visible range optics. We shall interpret the experimental data for (TMTTF)2X allowing to separate the critical relaxation within ferroelectric domains and the repolarization via sweeping of domain walls. We determine the critical slowing-down near the transition temperature, and the low frequency absorption coming from the creep of domain walls.

世話人　 市村　晃一
(ichimura@eng.hokudai.ac.jp)
北海道大学大学院工学研究院応用物理学部門

"Local and non-equilibrium processes in charge density waves"
Prof. Dr. Serguei Brazovskii

Jan 21, 2013

日本物理学会北海道支部講演会 共催: 第184回エンレイソウの会共催
講演題目：　Local and non-equilibrium processes in charge density waves
講　師　：　Prof. Dr. Serguei Brazovskii
　　　　　CNRS, University Paris-Sud, France
日　時　：　平成25年1月21日（月） 13:30-16:30
場　所　：　北海道大学 工学部大会議室(A1-17)

要　旨　：
This seminar will review resent experimental observations and their theoretical modeling in charge density waves (CDW). The results may be relevant to a broad class of low dimensional electronic systems with symmetry broken states ? the nearest extension is the ferroelectric charge ordering in organic conductors. The selected observations will be related to strong, topologically nontrivial perturbations of the order parameter under an external impact. The pattern may be static, induced by electric field or dynamic, under the optical pumping ? these are the two new trends in solid state physics [1]. Recent optical study of a far-from-equilibrium CDW recovered coherent aperiodic undulations of the order parameter, critical slowing down of the collective mode, and evolution of the particle-hole gap. Numerical modeling allowed interpreting the observations, particularly the spatio-temporal distortions arising from “earthquakes” - annihilation events of topological defects in depth of the sample. Strong perturbations were also found at the microscopic scale accessed by the STM; there are the amplitude solitons expected to play a role of neutral spin carriers - spinons. Experiments on nano-junctions in CDWs indicate on the intrinsic reconstruction by creating stationary and transient electronic vortices ? dislocations. The modeling shows that vortices are formed stepwise in the junction when the voltage across, or the current through, exceed a threshold. The vortex core concentrates the total voltage drop, working as a self-tuned microscopic tunnelling junction.
[1] http://lptms.u-psud.fr/impact2012/

世話人　 丹田　聡
(tanda@eng.hokudai.ac.jp)
北海道大学大学院工学研究院応用物理学部門