Nature Acta Medica Okayama 2399-3650 3 1 2020 Localized-to-itinerant transition preceding antiferromagnetic quantum critical point and gapless superconductivity in CeRh0.5Ir0.5In5 148 EN Shinji Kawasaki Department of Physics, Okayama University Toshihide Oka Department of Physics, Okayama University Akira Sorime Department of Physics, Okayama University Yuji Kogame Department of Physics, Okayama University Kazuhiro Uemoto Department of Physics, Okayama University Kazuaki Matano Department of Physics, Okayama University Jing Guo Institute of Physics, Chinese Academy of Sciences, Beijing National Laboratory for Condensed Matter Physics Shu Cai Institute of Physics, Chinese Academy of Sciences, Beijing National Laboratory for Condensed Matter Physics Liling Sun Institute of Physics, Chinese Academy of Sciences, Beijing National Laboratory for Condensed Matter Physics John L. Sarrao Los Alamos National Laboratory Joe D. Thompson Los Alamos National Laboratory Guo-Qing Zheng Department of Physics, Okayama University A fundamental problem posed from the study of correlated electron compounds, of which heavy-fermion systems are prototypes, is the need to understand the physics of states near a quantum critical point (QCP). At a QCP, magnetic order is suppressed continuously to zero temperature and unconventional superconductivity often appears. Here, we report pressure T-c. (P)-dependent In-115 nuclear quadrupole resonance (NQR) measurements on heavy-fermion antiferromagnet CeRh0.5Ir0.5In5. These experiments reveal an antiferromagnetic (AF) QCP at P-c(AF) = 1.2 GPa where a dome of superconductivity reaches a maximum transition temperature Tc. Preceding P-c(AF), however, the NQR frequency nu(Q) undergoes an abrupt increase at P-c* = 0.8 GPa in the zero-temperature limit, indicating a change from localized to itinerant character of cerium's f-electron and associated small-to-large change in the Fermi surface. At P-c(AF) where T-c is optimized, there is an unusually large fraction of gapless excitations well below T-c that implicates spin-singlet, odd-frequency pairing symmetry. No potential conflict of interest relevant to this article was reported.

Springer Nature Acta Medica Okayama 2041-1723 11 2020 Direction and symmetry transition of the vector order parameter in topological superconductors CuxBi2Se3 235 EN T. Kawai Department of Physics, Okayama University C. G. Wang Institute of Physics, Chinese Academy of Sciences, and Beijing National Laboratory for Condensed Matter Physics Y. Kandori Department of Physics, Okayama University Y. Honoki Department of Physics, Okayama University K. Matano Department of Physics, Okayama University T. Kambe Department of Physics, Okayama University Guo-qing Zheng Department of Physics, Okayama University Topological superconductors have attracted wide-spreading interests for the bright application perspectives to quantum computing. Cu0.3Bi2Se3 is a rare bulk topological superconductor with an odd-parity wave function, but the details of the vector order parameter d and its pinning mechanism are still unclear. Here, we succeed in growing CuxBi2Se3 single crystals with unprecedented high doping levels. For samples with x = 0.28, 0.36 and 0.37 with similar carrier density as evidenced by the Knight shift, the in-plane upper critical field Hc2 shows a two-fold symmetry. However, the angle at which the Hc2 becomes minimal is different by 90° among them, which indicates that the d-vector direction is different for each crystal likely due to a different local environment. The carrier density for x = 0.46 and 0.54 increases substantially compared to x ≤ 0.37. Surprisingly, the in-plane Hc2 anisotropy disappears, indicating that the gap symmetry undergoes a transition from nematic to isotropic (possibly chiral) as carrier increases. No potential conflict of interest relevant to this article was reported.