Metal Rich Plasma at the Center Portion of the Cygnus Loop

We observed the center portion of the Cygnus Loop supernova remnant with the ASCA observatory. The X-ray spectrum of the center portion was significantly different from that obtained at the North-East (NE) limb. The emission lines from Si and S were quite strong while those of O and the continuum emission were similar to those obtained at the NE limb. Based on the spectral analysis, Si and S emission lines originated from a high-kTe and low ionization plasma whereas O and most of the continuum emission arose from a low-kTe and high ionization plasma. We suppose that Si and S emitting gas are present at the interior of the Loop while O lines and continuum emission mainly arise from the shell region. Therefore, we subtracted the spectrum of the NE limb from that of the center. Obtained abundances of Si, S, and Fe were 4 $\pm$ 1, 6 $\pm$ 2, and ${1.3}^{+0.6}_{-0.3}$ times higher than those of the cosmic abundances, respectively, and are $\sim$40 times richer than those obtained at the NE limb. These facts strongly support that some of the crude ejecta must be left at the center portion of the Cygnus Loop. The low abundance of Fe relative to Si and S suggests a type II SN with a massive progenitor star as the origin of the Cygnus Loop.Comment: Accepted for Publications of the Astronomical Society of Japan, 40 pages, 12 Postscript figures, uses PASJ95.sty, PASJadd.sty, and psbox.st

Spontaneous two photon emission from a single quantum dot

Spontaneous two photon emission from a solid-state single quantum emitter is observed. We investigated photoluminescence from the neutral biexciton in a single semiconductor quantum dot coupled with a high Q photonic crystal nanocavity. When the cavity is resonant to the half energy of the biexciton, the strong vacuum field in the cavity inspires the biexciton to simultaneously emit two photons into the mode, resulting in clear emission enhancement of the mode. Meanwhile, suppression was observed of other single photon emission from the biexciton, as the two photon emission process becomes faster than the others at the resonance.Comment: 13 pages, 4 figure

Electronic phase diagram of La1.875_{1.875}Ba0.125−x_{0.125-x}Srx_xCuO4_4

We performed systematic measurements of magnetic susceptibility on single crystals of La$_{1.875}$Ba$_{0.125-x}$Sr$_x$CuO$_4$. The dependence of the superconducting transition temperature on Sr-concentration demonstrates a step-like pattern upon doping at {\it x}$\sim$0.08 as the crystal structure changes from low-temperature tetragonal (LTT) to low-temperature orthorhombic (LTO) phase at low temperature. Upon cooling, an anomalous upturn in the susceptibility was observed at the structural phase transition between the LTT-LTO phases under the magnetic field parallel to {\it c}-axis.Comment: 6 pages, 4 figures, Proceeding paper of the Stripes2000 conference in Roma, Ital

Nanoscale Heating of an Ultrathin Oxide Film Studied by Tip-Enhanced Raman Spectroscopy

We report on the nanoscale heating mechanism of an ultrathin ZnO film using low-temperature tip-enhanced Raman spectroscopy. Under the resonance condition, intense Stokes and anti-Stokes Raman scattering can be observed for the phonon modes of a two-monolayer (ML) ZnO on an Ag(111) surface, enabling us to monitor local heating at the nanoscale. It is revealed that the local heating originates mainly from inelastic electron tunneling through the electronic resonance when the bias voltage exceeds the conduction band edge of the 2-ML ZnO. When the bias voltage is lower than the conduction band edge, the local heating arises from two different contributions, namely direct optical excitation between the interface state and the conduction band of 2-ML ZnO or injection of photoexcited electrons from an Ag tip into the conduction band. These optical heating processes are promoted by localized surface plasmon excitation. Simultaneous mapping of tip-enhanced Raman spectroscopy and scanning tunneling spectroscopy for 2-ML ZnO including an atomic-scale defect demonstrates visualizing a correlation between the heating efficiency and the local density of states, which further allows us to analyze the local electron-phonon coupling strength with ∼2  nm spatial resolution

Fulde-Ferrell-Larkin-Ovchinnikov state in a perpendicular field of quasi two-dimensional CeCoIn5

A Fulde-Ferrell-Larkin-Ovchinnkov (FFLO) state was previously reported in the quasi-2D heavy fermion CeCoIn5 when a magnetic field was applied parallel to the ab-plane. Here, we conduct 115^In NMR studies of this material in a PERPENDICULAR field, and provide strong evidence for FFLO in this case as well. Although the topology of the phase transition lines in the H-T phase diagram is identical for both configurations, there are several remarkable differences between them. Compared to H//ab, the FFLO region for H perpendicular to the ab-plane shows a sizable decrease, and the critical field separating the FFLO and non-FFLO superconducting states almost ceases to have a temperature dependence. Moreover, directing H perpendicular to the ab-plane results in a notable change in the quasiparticle excitation spectrum within the planar node associated with the FFLO transition.Comment: 5 pages, 3 figure