arXiv subjects

M. Noda

Publications and source records attributed to M. Noda.

6 recordsLinked to original sources

arXiv2007

The Infrared Astronomical Mission AKARI

AKARI, the first Japanese satellite dedicated to infrared astronomy, was launched on 2006 February 21, and started observations in May of the same year. AKARI has a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey the sky in six wavelength bands from the mid- to far-infrared. The instruments also have the capability for imaging and spectroscopy in the wavelength range 2 - 180 micron in the pointed observation mode, occasionally inserted into the continuous survey operation. The in-orbit cryogen lifetime is expected to be one and a half years. The All-Sky Survey will cover more than 90 percent of the whole sky with higher spatial resolution and wider wavelength coverage than that of the previous IRAS all-sky survey. Point source catalogues of the All-Sky Survey will be released to the astronomical community. The pointed observations will be used for deep surveys of selected sky areas and systematic observations of important astronomical targets. These will become an additional future heritage of this mission.

astro-ph↗

arXiv2006

Charge transfer gap for T'-RE2CuO4 and T-La2CuO4 as estimated from Madelung potential calculations

T'-RE2CuO4 (RE: rare-earth element), after appropriate "reduction", has fairly high conductivity and also exhibits clear Fermi edge in photoemission spectroscopy. To clarify the origin of conductivity in the T' mother compounds, we evaluated the unscreened charge-transfer gap for T'-RE2CuO4 and T-La2CuO4. The value of charge-transfer gap for T'-compounds almost linearly decreases with increasing the ionic radius of RE from 12.24 eV for T'-Tm2CuO4 to 9.90 eV for T'-La2CuO4. The results qualitatively explain metallic conductivity in T'-RE2CuO4 for large RE.

cond-mat.supr-con↗

arXiv2005

IRTS observation of the near-infrared extragalactic background light

We searched for near-infrared extragalactic background light (EBL) in the data from the Near-InfraRed Spectrometer (NIRS) on the Infrared Telescope in Space (IRTS). After subtracting the contribution of faint stars and the zodiacal component based on modeling, a significant isotropic emission is obtained in the wavelength bands from 1.4 micron to 4.0 micron. The in-band flux amounts to ~ 35 nW m-2 sr-1 which is too bright to be explained by the integrated light from faint galaxies. Significant fluctuations in sky brightness were also detected which can not be explained by fluctuations due to faint stars, zodiacal components and normal galaxies. The excess fluctuation amounts to ~ 1/4 of the excess emission over the integrated light of galaxies. A two-point correlation analysis shows that IRTS/NIRS data has an angular scale of fluctuations of a few degrees. Recent WMAP results of CMB polarization indicate that the reionization of the Universe occurred at z ~ 17 or earlier. The observed near infrared background light could be redshifted UV light from the first generation of massive stars (Pop.III stars) which caused the reionization of the Universe. The spectral jump around 1 micron over the optical EBL suggests that massive star formation terminated at z~9. The observed fluctuations, however, are considerably larger than the theoretical predictions and require a new scenario for the Pop.III era.

astro-ph↗

arXiv2005

Role of impurity oxygen in superconductivity of "non-doped" T'-(La,RE)2CuO4

We have systematically investigated the effect of oxygen nonstoichiometry in a nominally undoped superconductor T'-(La,Y)2CuO4+y. In the experiments, the reduction condition was changed after the sample growth by MBE. The superconductivity is very sensitive to the reduction condition. With systematically increasingly reduced atmospheres, resistivity shows a continuous drop and no discontinuity is observed even until the appearance of superconductivity. The absence of the highly insulating state expected for Mott insulators around y ~ 0 suggests that T'-(La,Y)2CuO4 has intrinsic carriers. The role of residual apical oxygen, which is detrimental to superconductivity, is also discussed based on the resistivity-temperature characteristics in insufficiently reduced samples.

cond-mat.supr-con↗

arXiv2005

Origin of superconducting carriers in "non-doped" T'- (La,RE)2CuO4 (RE = Sm, Eu, Gd, Tb, Lu, and Y) prepared by molecular beam epitaxy

We have performed a systematic investigation of the variations of the lattice constants with substituent rare-earth element concentration x in the nominally undoped superconductors T'-(La3+)2-x(RE3+)xCuO4 (RE = Sm, Eu, Gd, Tb, Lu, and Y), which we have recently discovered using MBE. The results show both the in-plane and out-of-plane lattice constants (a0 and c0) linearly decrease with x, whose extrapolation to x = 2 agrees well with the reported a0 and c0 values for each T'-RE2CuO4. This behavior is what one would expect simply from the ionic size difference between La3+ and RE3+. The absence of the Cu-O bond stretching due to electron-doping, which is commonly observed in electron-doped T' and infinite-layer superconductors, implies that electron doping via oxygen deficiencies is, at least, not a main source of charge carriers.

cond-mat.supr-con↗

arXiv2005

New class of T-prime-structure cuprate superconductors

High-temperature superconductivity has been discovered in La2-xBaxCuO4 [1], a compound that derives from the undoped La2CuO4 crystallizing in the perovskite T-structure. In this structure oxygen octahedra surround the copper ions. It is common knowledge that charge carriers induced by doping in such an undoped antiferromagnetic Mott-insulator lead to high-temperature superconductivity [2- 4]. The undoped material La2CuO4 is also the basis of the electron-doped cuprate superconductors [5] of the form La2-xCexCuO4+y [6,7] which however crystallize in the so called T-prime-structure, i.e. without apical oxygen above or below the copper ions of the CuO2-plane. It is well known that for La2-xCexCuO4+y the undoped T-prime-structure parent compound cannot be prepared due to the structural phase transition back into the T-structure occuring around x ~ 0.05. Here, we report that if La is substituted by RE = Y, Lu, Sm, Eu, Gd, or Tb, which have smaller ionic radii but have the same valence as La, nominally undoped La2-xRExCuO4 can be synthesized by molecular beam epitaxy in the T-prime-structure. The second important result is that all these new T-prime-compounds are superconductors with fairly high critical temperatures up to 21 K. For this new class of cuprates La2-xRExCuO4, which forms the T-prime-parent compounds of the La-based electron doped cuprates, we have not been able to obtain the Mott-insulating ground state for small x before the structural phase transition into the T-structure takes place.

cond-mat.supr-con↗