Butsuri
Online ISSN : 2423-8872
Print ISSN : 0029-0181
ISSN-L : 0029-0181
Volume 73 , Issue 8
Showing 1-22 articles out of 22 articles from the selected issue
Preface
Contents
Trends
Reviews
Researches
  • Shinji Kawasaki, Guo-qing Zheng
    Type: Researches
    2018 Volume 73 Issue 8 Pages 558-563
    Published: August 05, 2018
    Released: March 12, 2019
    JOURNALS FREE ACCESS

    High temperature superconductivity appears in the cuprates when a spin order is destroyed, while the role of charge is less known. In this review, we describe our recent 63Cu-nuclear magnetic resonance study that discovered a long-range charge density wave (CDW) order in Bi2Sr2-x Lax CuO6+δ , setting in above the superconducting dome, under an in-plane field H||>10 T. The doping dependence of the onset temperature TCDW scales with the pseudogap temperature T *, which suggests that the T * is a high-temperature fingerprint of the CDW. The TCDW smoothly takes over the spin order temperature TN beyond a critical doping level at which superconductivity starts to emerge. These results provide new insights into the relationship between spin order, CDW and the pseudogap, and their connections to high-temperature superconductivity.

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  • Masashi Otani, Yasuhiro Kondo, Tsutomu Mibe
    Type: Researches
    2018 Volume 73 Issue 8 Pages 564-568
    Published: August 05, 2018
    Released: March 12, 2019
    JOURNALS FREE ACCESS

    A new experiment to measure anomalous magnetic moment and electric dipole moment of muon is proposed by introducing a new muon beam with low emittance. The experiment will examine the possible deviation from the standard model of particle physics that was indicated in the previous measurement. The low-emittance muon beam is realized by re-accelerating nearly-stopped muons. An experiment to accelerate negative muonium ions to 90 keV was carried out with a radio frequency quadrupole cavity. This is a first ever demonstration of muon acceleration with RF field.

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  • Ippei Danshita, Masaki Tezuka, Masanori Hanada
    Type: Researches
    2018 Volume 73 Issue 8 Pages 569-574
    Published: August 05, 2018
    Released: March 12, 2019
    JOURNALS FREE ACCESS

    We introduce the Sachdev–Ye–Kitaev (SYK) model, which was introduced in a condensed matter theoretical context but has quickly drawn attention as one of the candidate theories for the non-gravity side of the holography principle, also known as the gauge/gravity duality. The model is known to satisfy the chaos bound of the Lyapunov exponent as in the case of certain black holes. We then review the holography principle and the SYK model and introduce the out-of-time order correlator (OTOC), which reveals the Lyapunov exponent of a quantum chaotic system. Finally, we explain our proposal for the experimental realization of the SYK model using cold atoms and molecules in an optical lattice in a way that OTOC is measurable. Experimental realization of theories that define quantum gravity would pave the way to the experimental study of quantum gravity, where condensed matter theorists and cold atom experimentalists can contribute.

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  • Takaaki Takenaka, Takasada Shibauchi, Yoshifumi Tokiwa, Yuji Matsuda
    Type: Researches
    2018 Volume 73 Issue 8 Pages 575-580
    Published: August 05, 2018
    Released: March 12, 2019
    JOURNALS FREE ACCESS

    In exotic superconductors including high-Tc cuprates, the interactions mediating electron pairs are widely considered to have a magnetic rather than the conventional electron-phonon origin. Interest in such exotic pairing was initiated by the 1979 discovery of heavy-fermion superconductivity in CeCu2Si2 . A hallmark of unconventional pairing is that the superconducting energy gap changes sign as a function of electron momentum, often leading to gap nodes. Here we report low-temperature specific heat, thermal conductivity, and magnetic penetration depth measurements in CeCu2Si2 , demonstrating the absence of gap nodes at any point on the Fermi surface. Moreover, electron-irradiation experiments reveal that the full-gap superconductivity is extremely robust against impurities, implying that there is no sign change in the gap function. Our findings reveal that, contrary to the long-standing belief, heavy electrons with extremely strong Coulomb repulsion can condense into non sign-changing and fully gapped s-wave superconducting state, which has an on-site attractive pairing interaction.

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