[en] We have investigated the temperature variation of optical spectra for single crystals of Nd_2-xCe_xCuO₄ (0.05≤x≤0.15). While little temperature variation has been observed in the optical spectrum of the x=0.15 crystal, we have found a notable pseudogap as large as 0.2-0.4 eV at low temperature for the underdoped crystals (x<0.15). Drude-like response also evolves concomitantly with the pseudogap formation. The onset temperature (T*) of the pseudogap decreases with electron doping. The origin of the pseudogap has been ascribed to the antiferromagnetic correlation

[en] The authors have investigated the temperature variation of optical spectra comparatively for an oxygenated nonsuperconducting and a reduced superconducting crystal of Nd_1.85Ce_0.15CuO_4+y. Anomalous gap-like structure as large as 0.3 eV has been observed in the optical conductivity spectrum of the oxygenated crystal with lowering temperature from 340 K, while little temperature-variation has been observed for the reduced crystal. Furthermore, anomalies in lattice dynamics have been observed only for the oxygenated crystal in far-infrared spectra. These spectral signatures have shown parallel temperature-dependence, signaling a possible charge ordering in the oxygenated nonsuperconducting crystal

[en] The title material is known as an electron-doped high-T_C superconductor, while the as-grown sample is a semiconductor. The ⁶³Cu NMR studies for the as-grown and reduced Nd_1.85Ce_0.15CuO_4+δ single crystals were performed. The NMR spectra of both the samples show small and continuous distribution of ν_Q, which has nothing to do with the appearance/disappearance of superconductivity but may be structural in origin. Both crystals exhibit single-peaked central lines with different line width showing the single phase nature and no contamination of the other phase. The NMR signal of the as-grown sample disappears around 150 K due to the magnetic ordering. On the other hand, the line width of the reduced sample is narrower than that of the as-grown sample and shows weak temperature dependence. These behaviors indicate that the antiferromagnetic short range order is depressed when the sample is reduced

[en] We report a high-resolution angle-resolved photoemission spectroscopic study of the electron-doped (n -type) cuprate superconductor Nd_1.85 Ce_0.15 CuO₄ . We observe regions along the Fermi surface where the near-E_F intensity is suppressed and the spectral features are broad in a manner reminiscent of the high-energy ''pseudogap'' in the underdoped p -type (hole doped) cuprates. However, instead of occurring near the (π,0) region, as in the p -type materials, this pseudogap falls near the intersection of the underlying Fermi surface with the antiferromagnetic Brillouin zone boundary

No abstract available

[en] A YAG laser Thosmon scattering system for JT-60U has been developed to measure the pseudo-continuous time evolution of electron temperature and density profiles with 20 spatial channels. The target parameter ranges are 20 eV-20 keV for electron temperature and 5 x 10¹⁸ m^-3-2 x 10²⁰ m^-3 for electron density. The system consists of a Nd-YAG laser (1064 nm, 2 J, 10 Hz) and 20 polychromators with six spectral channels equipped with thermostabilized silicon avalanche photodiode detectors. The design, results and future plans are presented. (orig.)

[en] In CeCoIn₅, the thermal conductivity κ_xx and Hall conductivity κ_xy below T_c display large anomalies below T_c. The strong suppression of the anomalies in weak fields implies the existence of long-lived quasiparticles. We also discuss briefly the Wiedemann-Franz ratio and the existence of a strongly field-dependent spin-fluctuation heat current

[en] A Y-type hexaferrite Ba₂Mg₂Fe₁₂O₂₂ undergoes a transition to a proper-screw type helimagnetic structure with a propagation vector k₀ || [001] at 195 K, below which the system shows field-induced successive transitions under magnetic fields up to 1 T. Magnetization measurements also indicate the presence of the conical spin structure at low magnetic fields (∼ 10 mT) below about 50 K. We report on the magnetic control of the electric polarization in Ba₂Mg₂Fe₁₂O₂₂ with using the linearly oscillating fields up to ± 1 T at 5 K. The polarization vector can be cyclically reversed by weak magnetic fields of ± 30 mT. In addition, the polarization vector is repeatedly reversed without significant decay even by applying fields of ± 1 T, which suggests that the sense of the spin helix is somehow conserved in the process of the field-induced phase transitions. We propose that the conical spin structure carries the polarization vector upon the reversal of magnetic field.

[en] We have performed soft x-ray angle-resolved photoemission spectroscopy (ARPES) for the electron-doped high-temperature superconducting cuprates (HTSCs) Nd_2-xCe_xCuO₄ (x=0.075 and 0.15) in order to disclose their genuine bulk electronic structures. Our soft x-ray ARPES has revealed that the bulk-derived nodal 'kink' (the abrupt change of the electron velocity in quasiparticle dispersions), being absent in the low-energy ARPES, is clearly observable for the electron-doped superconducting Nd_1.85Ce_0.15CuO₄. This result confirms that the antiferromagnetic spin correlation is suppressed and the electron-phonon interactions are prevailing in the bulk of the electron-doped superconducting Nd_2-xCe_xCuO₄ at the optimal doping level. The nodal 'kink' behavior is equivalent to that observed in the hole-doped HTSCs. The anisotropic strong electron-phonon interactions seem to be inherent in the HTSCs irrespective of the type of doped carriers

[en] Full text: We report on the Fermi surface (FS) and the electronic structures of the n-type high-T_C cuprate Nd_1.85Ce₂CuO₄ (NCCO) probed for the first time by high-energy angle-resolved photoemission (ARPES) for hv = 416-700eV. Since the high-energy photoemission has an advantage in probing bulk states, the high-energy ARPES is powerful to reveal the bulk electronic structures and FSs of strongly correlated electron systems. The high-energy ARPES study was performed at BL25SU of SPring-8, where the energy resolution was set to 100meV. It is found that there is a hole-like Fermi surface centered at (π,π) in NCCO, which is qualitatively similar to the results of the so far reported low-energy (hv> 50eV) ARPES (angle-resolved photoemission). However, the spectral weight of the quasi-particle (QP) peak in the vicinity of the Fermi level along the nodal direction is much stronger at hv=500 and 700eV than that in the low-energy ARPES spectra. Surprisingly, this QP spectral weight is reduced at hv = 416 and 600eV. Our results suggest that the bulk electronic states of the quasi-two-dimensional superconductor NCCO are periodically changed with hv and thus changed as a function of momentum perpendicular to the conducting layer. Therefore, we conclude that a self-energy which has a lathreelr-dimensionality is responsible for the behavior of the bulk APRES spectra. We have also measured several core-levels and Ce 3d-4f resonance photoemission spectra including their polar-angle dependence to check the bulk-sensitivity. Clear differences in the spectral shapes are shown as a function of the polar-angle, indicating the noticeable different electronic states between the bulk and the surface