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A Mossbauer spectroscopy study of the iron-based superconductor KxFe2−ySe2, with two superconducting phases of SC1 and a pressure induced SC2 was performed under pressure. This compound consists of...

A Mössbauer spectroscopy study of the iron-based superconductor KxFe2−ySe2, with two superconducting phases of SC1 and a pressure induced SC2 was performed under pressure. This compound consists of two separated phases of major magnetic (non-superconducting) and minor superconducting components. The internal magnetic field of the major magnetic component decreased at the SC2 phase and disappeared around 15 GPa, while that of the minor non-magnetic component maintained its intensity up to 14.9 GPa. Multiple internal magnetic fields were introduced for improved fits to the spectra of the magnetic component at the SC2 phase, suggesting the importance of the electron–electron correlation in the emergence of the SC2 phase.

The effects of uniaxial strain and hydrostatic pressure on Y0.98Ca0.02Ba2Cu4O8 [called Y0.98(Ca0.02)-124] are investigated via AC magnetic measurements under stress corresponding to a pressure of (at most) 20 GPa. Hydrostatic contraction results in the largest enhancement of the superconducting transition temperature (Tc), whose maximum is 99 K, which is slightly lower than the maximum Tc achieved in YBa2Cu4O8 (called Y-124). The Meissner signal disappears at a hydrostatic pressure of approximately 15 GPa. This pressure region representing the Meissner signal is reduced by the out-of-plane contraction (along the c-axis), whereas it is increased by the in-plane contraction (along the c-plane). In the case of Y-124, both uniaxial contractions result in the disappearance of the Meissner signal at approximately 10 GPa prior to reaching the overdoped region. However, by doping Ca into the Y-site, we could investigate uniaxial strain effects characteristic of the so-called 124 structure without causing the stre...

The effects of uniaxial strain and hydrostatic pressure on YBa2Cu4O8 were investigated through magnetic measurements under stresses of up to 25 GPa. The out-of-plane (along the c-axis), in-plane (along the c-plane), and hydrostatic contractions all initially bring about an increase in the superconducting transition temperature (Tc). In the case of the out-of-plane and in-plane contractions, the Meissner signal disappears at a stress corresponding to about 10 GPa. However, under the hydrostatic contraction, the maximum Tc was about 100 K at 9–12 GPa, and the Meissner effect was observed at pressures of at least 16 GPa.

We obtained amorphous-FeAs-free SmFeAsO1-xFx using a low temperature sintering with slow cooling. SmFeAsO1-xFx is sintered at 980 {\deg}C for 40 hours and cooled slowly down to 600 {\deg}C. The low temperature sintering suppresses the formation of amorphous FeAs, and the slow cooling introduces much fluorine into SmFeAsO1-xFx. The superconductivity of this sample appears at 57.8 K and the superconducting volume fraction reaches 96 %. To study the change of fluorine concentration during the cooling process, samples are quenched by water at 950 {\deg}C, 900 {\deg}C, 850 {\deg}C, 800 {\deg}C, 750 {\deg}C and 700 {\deg}C. It is found that fluorine is substituted not only at the maximum heating temperature but also during the cooling process. The low temperature sintering with slow cooling is very effective to obtain a homogeneous SmFeAsO1-xFx with high fluorine concentration., Comment: 17 pages, 7 figures

We have successfully synthesized the new BiS2-based superconductor NdOBiS2 by F doping. This compound is composed of superconducting BiS2 layers and blocking NdO layers, which indicates that the BiS2 layer is analogous to the CuO2 layer in cuprates or to the Fe–As layer in Fe-based superconductors. We can obtain NdO1-xFxBiS2 with bulk superconductivity by a solid-state reaction. Therefore, NdO1-xFxBiS2 should be a suitable material for elucidating the mechanism of superconductivity in the BiS2 layer.

We have fabricated thin films of FeTe 1- x Se x using a scotch-tape method. The superconductivities of the thin films are different from each other although these films were fabricated from the same bulk sample. The result clearly presents the inhomogeneous superconductivity in FeTe 1- x Se x . The difference might arise from inhomogeneity due to the excess Fe concentration. The resistivity of a thin film with low excess Fe shows good superconductivity with the sharp superconducting-transition width and more isotropic superconductivity.

The uniaxial strain effects on the cuprate superconductor YBa 2 Cu 4 O 8 (Y-124) were investigated by magnetic measurements and quantitatively compared with those of hydrostatic contraction up to 1...