Taiki Yoshinaka

The University of Tokyo, Tōkyō, Japan

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Publications (4)4.06 Total impact

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    ABSTRACT: We report a reproducible synthetic method for superconducting Cu-intercalated Bi2Se3 by an improved melt growth method. Avoiding the production of Cu2Se, which has a higher melting point than that of Bi2Se3, and quenching Cu--Bi--Se mixtures at the liquid phase are keys to obtaining good superconducting samples in a reproducible manner.
    Journal of the Physical Society of Japan 06/2013; 82(6):3702-. DOI:10.7566/JPSJ.82.063702 · 1.48 Impact Factor
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    ABSTRACT: CuxBi2Se3(Tc ˜3.8 K)[1] is a promising candidate material to be a topological superconductor, and it is very important to clarify the origin of its superconductivity. However, CuxBi2Se3 synthesized by Hor et al. does not show zero resistivity below Tc [1], and some concerns still remain in the quality of samples. Recently, several groups reported the successful preparation of Cu-intercalated Bi2Se3 with zero resistivity by an electrochemical method [2] and the Bridgman method [3]. Here, we report transport properties of single crystals of CuxBi2Se3 with zero resistivity prepared by the Bridgman method. We stress that the process of the quenching from a temperature of about 1000 K into cold water is of crucial importance in the crystal growth process. The grown crystal with x=0.10 shows zero resistivity at about 3.2 K. We also report the results of the intercalations of different metal elements [4].[4pt] [1] Y. S. Hor et al., PRL 104 (2010) 057001.[0pt] [2] M. Kriener et al., PRL 106 (2011) 127004.[0pt] [3] T. Kirzhner et al., arXiv:1111.5805. T. V. Bay et al., arXiv:1112.0102.[0pt] [4] Y. Imai et al., J. Phys. Soc. Jpn. 81 (2012) 113708.
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    ABSTRACT: We investigate bulk superconductivity in a high-quality single crystal of Bi2Pd (β-Bi2Pd; space group: I4/mmm) with a superconducting transition temperature of 5.4 K, by exploring its electrical resistivity, magnetic susceptibility, and specific heat. The temperature dependence of the electrical resistivity shows convex-upward behavior at temperatures greater than 40--50 K, which can be explained using a parallel-resistor model. In addition, the temperature dependences of the upper critical magnetic field and the specific heat suggest that β-Bi2Pd is a multiple-band/multiple-gap superconductor.
    Journal of the Physical Society of Japan 11/2012; 81(11):3708-. DOI:10.1143/JPSJ.81.113708 · 1.48 Impact Factor
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    ABSTRACT: We study microwave surface impedance measurements of LiFeAs, LiFe(As,P) and FeSe1−xTex single crystals. The in-plane penetration depths of LiFeAs and LiFe(As,P) depend on temperature exponentially at low temperatures, which is a strong indication that these two materials have the nodeless superconducting gap. The temperature dependence of the superfluid density indicates that LiFeAs and LiFe(As,P) are multi-gap superconductors with at least two isotropic gaps. In FeSe1−xTex, on the other hand, the quadratic temperature dependence of the in-plane penetration depth appears, which indicates the existence of some sort of quasiparticle excitations. In addtion, the real part of the microwave conductivity exhibits a large enhancement below Tc in all three materials, which results from the increase of the quasiparticle relaxation time, τ, below Tc.
    Physica C Superconductivity 11/2011; 471(s 21–22):630–633. DOI:10.1016/j.physc.2011.05.013 · 1.11 Impact Factor