"Ultrafast Laser-generated Coherent Waves in Advanced Materials: From the Academic Lab to the Real World and Back"
Prof. Keith A. Nelson

Nov 11, 1998



講演題目: Ultrafast Laser-generated Coherent Waves in Advanced Materials: From the Academic Lab to the Real World and Back
講 師 : Prof. Keith A. Nelson
     MIT
日 時 : 平成10年11月11日 (水) 14:00-
場 所 : 電子科学研究所講堂(事務棟 2F)

要 旨 :
Coherent waves are generated and monitored optically in bulk and thin film materials to provide fundamental insight into their structures and dynamics; to exert optical control over their behavior; and to provide information ofimmediate practical value. On picosecond and nanosecond time scales, acoustic waves are characterized to learn about structural phase transitions and relaxation dynamics in crystals, polymers, and viscous liquids. In thin films, the measured acoustic responses yield the film elastic moduli, thermal diffusivities, and thicknesses, as well as a simple check for film-substrate delamination. This has led to the successful commercialization of the measurement method which is now used in the microelectronics industry. In ferroelectric crystalline solids, high-frequency vibrational waves which move through the lattice at a significant fraction of the speed of light are generated with femtosecond pulses and pulse sequences. Their responses teach us about ferroelectric phase transitions, anharmonic potential energy surfaces and nonlinear lattice dynamics, and the prospects for optical control over collective material behavior. The results illustrate the interplay between fundamental spectroscopic research on complex materials and the practical applications that may emerge.

世話人  八木 駿郎
(toyagi@es.hokudai.ac.jp)
北海道大学・大学院理学研究科・物理学専攻

Category: 支部講演会 | Static URL: /seminar/19981111.htm | Edit
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"STM vortex core spectroscopy and non conventional pairing in high temperature superconductors"
Christophe Renner

Nov 11, 1998



講演題目: STM vortex core spectroscopy and non conventional pairing in high temperature superconductors
講 師 : Christophe Renner
     University of Geneva
日 時 : 平成10年11月20日 (金) 15:30-17:00
場 所 : 北海道大学理学部2号館4階409講義室

要 旨 :
The quasiparticle density of states is a key ingredient in the quest for the mechanism of high temperature superconductivity. One of the common features of high- and low-temperature superconductors is a gap in the quasiparticle excitation spectrum at the Fermi level related to the carrier pairing below the superconducting transition temperature ( T c). However, in high temperature superconductors (HTS), its characteristics are very unusual and depart highly from the BCS predictions. One of the striking spectroscopic signatures of HTS is the persistence of a gap in the normal state above T c. Tunneling spectroscopy shows that this normal state gap is intimately related to the superconducting gap. Recently, it was put into a new perspective as it was also found at low temperature inside the vortex cores of Bi2Sr2CaCu2O8 by scanning tunneling spectroscopy. These latest results are consistent with the existence of incoherent pairing states in the normal state above T c and inside the vortex cores below T c. They suggest that these materials are in an intermediate regime between BCS and Bose-Einstein condensation.

世話人  小田 研
(moda@sci.hokudai.ac.jp)
北海道大学・大学院理学研究科・物理学専攻

Category: 支部講演会 | Static URL: /seminar/19981120.htm | Edit
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