We have studied the anisotropy in the in-plane resistivity and the electronic structure of isovalent Ru-substituted BaFe 2 As 2 in the antiferromagnetic-orthorhombic phase using well-annealed crystals. The anisotropy in the residual resistivity component increases in proportional to the Ru dopant concentration, as in the case of Co-doped compounds. On the other hand, both the residual resistivity and the resistivity anisotropy induced by isovalent Ru substitution is found to be one order of magnitude smaller than those induced by heterovalent Co substitution. Combined with angle-resolved photoemission spectroscopy results, which show almost the same anisotropic band structure both for the parent and Ru-substituted compounds, we confirm the scenario that the anisotropy in the residual resistivity arises from anisotropic impurity scattering in the magnetostructurally ordered phase rather than directly from the anisotropic band structure of that phase.

We systematically investigated the anisotropic in-plane resistivity of the iron telluride including three kinds of impurity atoms: excess Fe, Se substituted for Te, and Cu substituted for Fe. Sizable resistivity anisotropy was found in the magneto-structurally ordered phase whereas the sign is opposite (ρ a > ρ b , where the b-axis parameter is shorter than the a-axis one) to that observed in the transition-metal doped iron arsenides (ρ a < ρ b ). On the other hand, our results demonstrate that the magnitude of the resistivity anisotropy in the iron tellurides is correlated with the amount of impurities, implying that the resistivity anisotropy originates from an exotic impurity effect like that in the iron arsenides. This suggests that the anisotropic carrier scattering by impurities is a universal phenomenon in the magneto-structurally ordered phase of the iron-based materials.

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The saturation of SiPMs is a potential issue for scintillator calorimeters with SiPM readout. When a large number of particles hit a scintillator, the SiPM output can be saturated due to the limited number of pixels. In order to convert the SiPM output into the number of incident photons correctly, it is necessary to understand the behavior of the SiPM saturation.The saturation curve is usually measured by directly injecting a fast laser pulse (∼400 nm) to a SiPM. However, the effect of the time constant of the scintillation light emission, which is not negligible compared to the recovery time of the SiPM pixel, is not included in this method. We propose a new method to measure the SiPM saturation with scintillation light excited by an UV laser. The measured saturation curve can directly be used for the saturation correction of the calorimeter response, since the effect of the cell recovery during the scintillation emission is included.A fast fs UV pulse laser with a wavelength of 190 nm is used. The 190 nm laser causes scintillation excitation, whereas it is invisible to the SiPM. The laser is injected to a plastic scintillator coupled to a SiPM. For comparison, the same test is carried out also by injecting a fast laser pulse with a wavelength of 470 nm. The saturation curve is obtained for a wide range of N pe , and a large over-saturation is observed for the 190 nm injection, which is significantly larger than the 470 nm injection. This difference is the effect of the time constant of the scintillation emission, and can have a big impact on the saturation correction. K: Photon detectors for UV, visible and IR photons (solid-state); Calorimeters; Scintillators, scintillation and light emission processes (solid, gas and liquid scintillators) 1Corresponding author.

We have investigated the superconducting gap of optimally doped Ba(Fe0.65Ru0.35)2As2 by angle-resolved photoemission spectroscopy (APRES) using bulk-sensitive 7 eV laser and synchrotron radiation. It was found that the gap is isotropic in the kx-ky plane both on the electron and hole Fermi surfaces (FSs). The gap magnitudes of two resolved hole FSs show similar kz dependences and decrease as kz approaches ~2c (i.e., around the Z point) unlike the other Fe-based superconductors reported so far, where the superconducting gap of only one hole FS shows a strong kz dependence. This unique gap structure can be understood in the scenario that the 2 orbital character is mixed into both hole FSs due to the finite spin-orbit coupling between almost degenerate FSs and is reproduced by calculations within the random phase approximation including the spin-orbit coupling.The momentum dependence of the superconducting (SC) order parameter in the Fe-based superconductors (FeSCs) has been intensively investigated by angleresolved photoemission spectroscopy (ARPES) due to their close relationship with paring mechanisms. A variety of superconducting gap symmetries in FeSCs, such as s±-wave, nodeless s++ and nodal s-wave, have been discussed from the theoretical point of view [1,2]. Up to now, even for the most intensively studied 122 systems, the situation is still complicated. As for the isovalently substituted BaFe2(As1-xPx)2 compound, it was revealed by the penetration depth and thermal conductivity measurements that there exist line nodes in the SC gap (for x = 0.33) [3]. It has been pointed out based on the random phase approximation (RPA) calculation that, three-dimensional (3D) horizontal line nodes may appear around the Z point [k = (0, 0, 2/c)] on the outermost strongly warped hole Fermi surface (FS) which has dominantly 2 orbital character [4]. However, ARPES experiments have not come to agreement on the existence of the horizontal line nodes on the 3D hole FS of BaFe2(As0.7P0.3)2 [5, 6].Ba(Fe1-xRux)2As2, another isovalently substituted system, in which doping is done at the pivotal Fe site [7,8], also exhibits a highly warped hole FS along the kz direction [9, 10]. Recent thermal conductivity measurements suggest that Ba(Fe1-xRux)2As2 has also SC gap line nodes for a wide doping range [11]. In order to clarify the SC gap structure and the location of the suggested line nodes in momentum space, we performed an ARPES study of optimally doped Ba(Fe0.65Ru0.35)2As2.In this study, two kinds of APRES apparatus were employed: one is bulk-sensitive ARPES using a vacuum ultraviolet laser; the other is based on synchrotron radiation, which allows us to trace the kz dependence of the SC gap by tuning the incident photon energy. We show that the SC gaps both on the hole FSs and electron FSs are isotropic in the kx-ky plane, while the SC gaps on the hole FSs are strongly kz dependent. Interestingly, both of the two resolved hole FSs exhibit SC gaps with almost the same kz dependence and magnitudes. We attribute this unique observat...