arXiv subjects

Ryota Sogabe

Publications and source records attributed to Ryota Sogabe.

5 recordsLinked to original sources

arXiv2019

High-pressure synthesis and superconducting properties of NaCl-type In1-xPbxTe (x = 0-0.8)

We have investigated the Pb-substitution effect on the superconductivity of NaCl-type In1-xPbxTe samples obtained using high-pressure synthesis. Polycrystalline samples with x = 0-0.8 were obtained, and the lattice parameter systematically increased by Pb substitution. The superconducting transition temperature (Tc ~3 K for x = 0) increased to 5.3 K (for x = 0.4) by Pb substitutions. According to the comparison of the electronic states between NaCl-type InTe and PbTe, we consider that the Pb substitution increases electron carriers. Possible mechanisms of the enhancement of Tc in this system have been discussed on the basis of conventional pairing mechanism and the possibility of the relation to the valence-skipping state of In.

cond-mat.supr-con↗

arXiv2019

Improvement of superconducting properties by high mixing entropy at blocking layers in BiS2-based superconductor REO0.5F0.5BiS2

To investigate the interlayer interaction in the recently synthesized high-entropy-alloy-type (HEA-type) REO0.5F0.5BiS2 superconductors (RE: rare earth), we have systematically synthesized samples with close lattice parameters and different mixing entropy (DSmix) for the RE site. The crystal structure was investigated using synchrotron X-ray diffraction and Rietveld refinement. For the examined samples with different DSmix, the increase in DSmix does not largely affect the bond lengths and the bond angle of the BiS2 conducting layer but clearly suppresses the in-plane disorder at the in-plane S1 site, which is the parameter essential for the emergence of bulk superconductivity in the REO0.5F0.5BiS2 system. Bulk nature of superconductivity is enhanced by the increase in DSmix for the present samples. The results of this work clearly show that the increase in mixing entropy at the blocking layer can positively affect the emergence of bulk superconductivity in the conducting layer, which is the evidence of the interaction between the high entropy states of the blocking layers and the physical properties of the conducting layers.

cond-mat.supr-con↗

arXiv2018

Superconductivity in La1-xCexOBiSSe: carrier doping by mixed valence of Ce ions

We report the effects of Ce substitution on structural, electronic, and magnetic properties of layered bismuth-chalcogenide La1-xCexOBiSSe (x = 0-0.9), which are newly obtained in this study. Metallic conductivity was observed for x > 0.1 because of electron carriers induced by mixed valence of Ce ions, as revealed by bond valence sum calculation and magnetization measurements. Zero resistivity and clear diamagnetic susceptibility were obtained for x = 0.2-0.6, indicating the emergence of bulk superconductivity in these compounds. Dome-shaped superconductivity phase diagram with the highest transition temperature (Tc) of 3.1 K, which is slightly lower than that of F-doped LaOBiSSe (Tc = 3.7 K), was established. The present study clearly shows that the mixed valence of Ce ions can be utilized as an alternative approach for electron-doping in layered bismuth-chalcogenides to induce superconductivity.

cond-mat.supr-con↗

arXiv2018

Superconductivity in REO0.5F0.5BiS2 with high-entropy-alloy-type blocking layers

We synthesized new REO0.5F0.5BiS2 (RE: rare earth) superconductors with the high-entropy-alloy-type (HEA-type) REO blocking layers. According to the RE concentration and the RE ionic radius, the lattice constant of a systematically changed in the HEA-type samples. A sharp superconducting transition was observed in the resistivity measurements for all the HEA-type samples, and the transition temperature of the HEA-type samples was higher than that of typical REO0.5F0.5BiS2. The sharp superconducting transition and the enhanced superconducting properties of the HEA-type samples may indicate the effectiveness of the HEA states of the REO blocking layers in the REO0.5F0.5BiS2 system.

cond-mat.supr-con↗

arXiv2017

Bulk Superconductivity Induced by Se Substitution in BiCh2-Based Layered Compounds Eu0.5Ce0.5FBiS2-xSex

We report the effect of Se substitution on the crystal structure and superconductivity of BiCh2-based (Ch: S, Se) layered compounds Eu0.5Ce0.5FBiS2-xSex (x = 0-1). Crystal structure analysis showed that both lattice constants, a and c, increased with increasing x, which is different from the related La-doped system, such as Eu0.5La0.5FBiS2-xSex. This is due to Se substitution for both in-plane and out-of-plane Ch sites in the present Ce-doped system. Zero resistivity was observed for x = 0.2-1 above 2 K. Superconducting properties of Eu0.5Ce0.5FBiS2-xSex was investigated by magnetic susceptibility, and the highest superconducting transition temperature of 3.5 K was obtained for x = 0.6 with a large shielding volume fraction. The emergence of bulk superconductivity and metallic conductivity can be qualitatively described in terms of increased in-plane chemical pressure effect. A magnetic anomaly below 8 K, probably because of ferromagnetic order of magnetic moment of Ce3+ ions, coexists with bulk superconductivity in BiCh2 layer. Since the effect of Se substitution on the magnetic transition temperature is ignorable, we suggest that the coupling between the magnetic order at the (Eu,Ce)F layer and superconductivity at the Bi(S,Se)2 layer is weak.

cond-mat.supr-con↗