Coexistence of the Charge-Density-Wave Phase in the Photo-Induced Metallic Phase in 1T-TaS2

We investigate the nonequilibrium electronic structure of 1T-TaS2 by time- and angle-resolved photoemission spectroscopy. We observe that strong photo excitation induces collapse of the Mott gap, leading to the photo-induced metallic phase. It is also found that the oscillation of photoemission intensity occurs as a result of the excitations of coherent phonons corresponding to the amplitude mode of the charge density wave (CDW). To study the dynamical change of the band dispersions modulated by the CDW amplitude mode, we perform analyses by using frequency-domain angle-resolved photoemission spectroscopy. We find that two different peak structures exhibit anti-phase oscillation with respect to each other. They are attributed to the minimum and maximum band positions in energy, where the single band is oscillating between them synchronizing with the CDW amplitude mode. We further find that the flat band constructed as a result of CDW band folding survive with the collapse of Mott gap. Our results strongly suggest the CDW phase is more robust than the Mott insulating phase, and the lattice modulation corresponding to the CDW amplitude mode dynamically modulate the Mott gap.Comment: 6 pages, 5 figure

Quantum Phase Extraction in Isospectral Electronic Nanostructures

Quantum phase is not a direct observable and is usually determined by interferometric methods. We present a method to map complete electron wave functions, including internal quantum phase information, from measured single-state probability densities. We harness the mathematical discovery of drum-like manifolds bearing different shapes but identical resonances, and construct quantum isospectral nanostructures possessing matching electronic structure but divergent physical structure. Quantum measurement (scanning tunneling microscopy) of these "quantum drums" [degenerate two-dimensional electron states on the Cu(111) surface confined by individually positioned CO molecules] reveals that isospectrality provides an extra topological degree of freedom enabling robust quantum state transplantation and phase extraction.Comment: Published 8 February 2008 in Science; 13 page manuscript (including 4 figures) + 13 page supplement (including 6 figures); supplementary movies available at http://mota.stanford.ed

A biominősítés hatása a fogyasztók érzékelésére és attitűdjére csokoládék esetén

The time–energy information of ultrashort X-ray free-electron laser pulses generated by the Linac Coherent Light Source is measured with attosecond resolution via angular streaking of neon 1s photoelectrons. The X-ray pulses promote electrons from the neon core level into an ionization continuum, where they are dressed with the electric field of a circularly polarized infrared laser. This induces characteristic modulations of the resulting photoelectron energy and angular distribution. From these modu- lations we recover the single-shot attosecond intensity structure and chirp of arbitrary X-ray pulses based on self-amplified spontaneous emission, which have eluded direct measurement so far. We characterize individual attosecond pulses, including their instantaneous frequency, and identify double pulses with well-defined delays and spectral properties, thus paving the way for X-ray pump/X-ray probe attosecond free-electron laser science

Properties of novel silicon nitride-based materials

Our research on the mechanical and thermal properties of magnesium silicon nitride (MgSiN2)-silicon nitride (Si3N4) composite specimens has been reviewed in this paper. The specimen was fabricated by hot-pressing the compressed powder at a temperature between 1550°C and 1700°C for 90 min under a pressure of 75 MPa in a nitrogen atmosphere, using 1 mol% ytterbium oxide (Yb2O3) addition as a sintering aid. Mechanical and thermal properties of MgSiN2 specimen without Si3N4 addition were as follows: Vickers hardness, 18.3 GPa; flexural strength, 371 MPa; fracture toughness, 2.2 MPa m1/2; and thermal conductivity, 22.7 W m-1 K-1. In order to improve these properties, MgSiN2 composite was fabricated with the addition of 0-89 mol% Si3N4. The fracture toughness of MgSiN2 specimen could be enhanced by the addition of Si3N4, e.g., 6.6 MPa m1/2 (4 mol% Si3N4 addition) and 8.7 MPa m1/2 (49 mol% Si3N4 addition). An increase in fracture toughness of MgSiN2-Si3N4 specimen was attributed to the elongation of Si3N4 grains. Moreover, the thermal conductivity of MgSiN2-Si3N4 specimen increased to 32.7 W m-1 K-1 for 29 mol% Si3N4 addition

Research on ceramics in Japan

Er wordt een overzicht gegeven van het huidige onderzoek aan keramiek in Japan, waarbij aandacht wordt besteed aan Japanse onderzoeksinstellingen, onderzoekstrends en financiering. Nationale onderzoeksinstellingen doen pionierend onderzoek met het oog op industrialisatie door samenwerking tussen overheid, universiteiten en industrie. Naast het verzorgen van onderwijs, voeren universiteiten onderzoek uit gericht op vrije ideeën van individuele wetenschappers. De grote bedrijven richten zich op toegepast onderzoek en ontwikkelingswerk.Verder wordt in dit artikel een indruk gegeven van de bijdrage van academische verenigingen aan informatieuitwisseling, en ingegaan op de financiering van wetenschappelijk onderzoek door de Japanse overheid