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Substitution of Y for Ca in the Bi2Sr2CaCu2O8+δ (Bi-2212) system is known to effectively change the hole carrier density. In this paper, we report the growth and characterization of Y-substituted Bi-2212 whisker crystals. The evaluated Y content in the whiskers increased as we increased the nominal Y-ratio in the Bi–Sr–Ca–Y–Cu–Te precursor. The X-ray diffraction patterns of whiskers aligned on a glass plate only showed (00l) Bragg peaks of the Bi-2212 phase, indicating that the grown whiskers are single crystalline. The c-axis lattice parameter showed a monotonic decrease with Y-substitution. The resistivity of Y-substituted whiskers showed a systematic decrease in superconducting transition temperature and an increase in normal resistivity, suggesting that the hole carrier density was controlled via Y-substitution. Based on these results, we propose that Bi-2212 with various carrier concentrations can be easily obtained by growing Y-substituted whiskers. Furthermore, such whiskers with controlled T c might be useful for microelectronic applications such as terahertz oscillators.

Cuprate superconductor Bi2Sr2CaCu2O8+δ (BSCCO) has been a promising candidate of a coherent, continuous, and compact THz light source owing to its intrinsic Josephson junction (IJJ) inside the crystal structure. In this paper, we utilized BSCCO cross-whisker (CW) junctions to produce THz emitter device using the whisker crystals which can be easily obtained compared with single crystals. As a result, we have successfully observed the emission from the CW IJJ at the frequency of ∼0.7 THz, which is the first observation of a THz emission from whiskers to our knowledge. Our findings would enlarge the applicability of BSCCO superconductors for compact THz emission sources.

A diamond anvil cell (DAC) has become an effective tool for investigating physical phenomena that occur at extremely high pressure, such as high-transition temperature superconductivity. Electrical transport measurements, which are used to characterize one of the most important properties of superconducting materials, are difficult to perform using conventional DACs. The available sample space in conventional DACs is very small and there is an added risk of electrode deformation under extreme operating conditions. To overcome these limitations, we herein report the fabrication of a boron-doped diamond microelectrode and undoped diamond insulation on a beveled culet surface of a diamond anvil. Using the newly developed DAC, we have performed in-situ electrical transport measurements on sulfur hydride H2S, which is a well-known precursor of the pressure-induced, high-transition temperature superconducting sulfur hydride, H3S. These measurements conducted under high pressures up to 192 GPa, indicated the presence of a multi-step superconducting transition, which we have attributed to elemental sulfur and possibly HS2.

CsBi4-x Pb x Te6 is synthesized and the superconductivity associated with the structural transition from Pb substitution is studied. Photoemission spectroscopy measurements are performed in order to elucidate the relationship between the electronic structure and the occurrence of the superconductivity. When Bi is substituted with Pb, an electron doping-like change in the electronic structure is directly observed which is contrary to the naive expectation of hole doping. This observation is consistent with band structure calculations and appears to be a unique characteristic of CsBi4-x Pb x Te6 because of the dissociation of Bi dimers upon Pb substitution. These results indicate that it may be possible to control the electron and hole doping via manipulating the Bi dimers through Pb substitution.

Isovalent substitution of S by Se in LaOBiS2-x Se x has a substantial effect on its electronic structure and thermoelectric properties. To investigate the possible role of BiS2 structural instability, we have studied the local structure of LaOBiS2-x Se x ([Formula: see text]) using temperature dependent Bi L3-edge extended x-ray absorption fine structure measurements. The results reveal that the local structure of the two compounds is significantly different. The BiS2 sub-lattice is largely distorted in LaOBiS2 (x = 0.0), with two in-plane Bi-S1 distances separated by ∼0.4 A instead LaOBiSSe (x = 1.0) showing much smaller local disorder with two in-plane Bi-Se distances in the plane being separated by ∼0.2 A. Temperature dependent study shows that the two Bi-S1 distances are characterized by different bond strength in LaOBiS2 (x = 0.0) while it is similar for the Bi-Se distances in LaOBiSSe (x = 1.0). The out of plane Bi-S2 bond is harder in LaOBiSSe indicating that the structural instability of BiS2 layer has large effect on the out-of-plane atomic correlations. The results suggest that the local structure of LaOBiS2-x Se x is an important factor to describe differing electronic and thermal transport of the two compounds.

Synchrotron-based angle-resolved photoemission spectroscopy is used to determine the electronic structure of layered SnSe, which was recently turned out to be a potential thermoelectric material. We observe that the top of the valence band consists of two nearly independent hole bands, whose tops differ by ~20 meV in energy, indicating the necessity of a multivalley model to describe the thermoelectric properties. The estimated effective masses are anisotropic, with in-plane values of 0.16-0.39 m$_0$ and an out-of-plane value of 0.71 m$_0$, where m$_0$ is the rest electron mass. Information of the electronic structure is essential to further enhance the thermoelectric performance of hole-doped SnSe., Comment: 14 pages including 2 figures + 2 pages of supplementary data

BiS2-based layered superconductors are new superconductors, having been paid special attention due to the layered crystal structure and the characteristic electronic structure that can lead to exotic mechanism of superconductivity as well as cooperation of superconductivity and ordered phases. In this article, we report valence band dispersions and Fermi surface topology of LaO1-xFxBiS2 (x = 0.23, Tc < 2 K) studied by angle-resolved photoemission spectroscopy, and compared them with those of LaO1-xFxBiS2 (x = 0.46, Tc = 3.1 K). We discuss experimental x dependent electronic structures and its relation to Tc. We also point to anomalous spectroscopic features in LaO1-xFxBiS2 (x = 0.46) that can be explained by band structure calculations considering distorted lattice, suggesting role of dynamical or static lattice distortion to the physical properties.

Bulk electronic structure of novel layered superconductor Nd(O,F)BiS2 was studied by using soft x-ray angle-resolved photoelectron spectroscopy (ARPES). Electron-like Fermi surface centered at the X(R) point was observed, consistent with earlier ARPES reports on surface-sensitive VUV light source. Based on the comparison of the electronic structure between Nd(O,F)BiS2 and La(O,F)BiS2, we discuss possible important factors for the superconductivity in this series of material.

We have measured the temperature-dependent X-ray diffraction pattern of a single-crystalline EuO (100) thin film to investigate the change of the lattice constant due to the ferromagnetic phase transition. No structural transition was observed and the contracting rate of the lattice constant was dramatically increases below the ferromagnetic phase transition temperature. It indicates that the hybridization intensity between the Eu 4f state and the other O 2p and Eu 5d states increases in the ferromagnetic phase.