"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
