The lifetime of a Lambda particle embedded in a nucleus (hypernucleus) decreases from that of free Lambda decay due to the opening of the Lambda N to NN weak decay channel. However, it is generally believed that the lifetime of a hypernucleus attains
a constant value (saturation) for medium to heavy hypernuclear masses, yet this hypothesis has been difficult to verify. The present paper reports a direct measurement of the lifetime of medium-heavy hypernuclei produced with a photon-beam from Fe, Cu, Ag, and Bi targets. The recoiling hypernuclei were detected by a fission fragment detector using low-pressure multi-wire proportional chambers. The experiment agrees remarkably well with the only previously-measured single-species heavy-hypernucleus lifetime, that of Fe56_Lambda at KEK, and has significantly higher precision. The experiment disagrees with the measured lifetime of an unknown combination of heavy hypernuclei with 180<A<225 and, with a small statistical and systematic uncertainty, strongly favors the expected saturation of the lifetime decrease.
The thermal conductivity of optimally doped NaFe$_{0.972}$Co$_{0.028}$As ($T_c sim$ 20 K) and overdoped NaFe$_{0.925}$Co$_{0.075}$As ($T_c sim$ 11 K) single crystals were measured down to 50 mK. No residual linear term $kappa_0/T$ is found in zero ma
gnetic field for both compounds, which is an evidence for nodeless superconducting gap. Applying field up to $H$ = 9 T ($approx H_{c2}/4$) does not noticeably increase $kappa_0/T$ in NaFe$_{1.972}$Co$_{0.028}$As, which is consistent with multiple isotropic gaps with similar magnitudes. The $kappa_0/T$ of overdoped NaFe$_{1.925}$Co$_{0.075}$As shows a relatively faster field dependence, indicating the increase of the ratio between the magnitudes of different gaps, or the enhancement of gap anisotropy upon increasing doping.
The interplay between magnetism and superconductivity has been a central issue in unconventional superconductors. While the dynamic magnetism could be the source of electron pairing, the static magnetism is generally believed to compete with supercon
ductivity. In this sense, the observation of Q phase, the coupled spin-density wave order and superconductivity, in the heavy-fermion superconductor CeCoIn5 is very puzzling. Whether this Q phase origins from the novel Fulde-Ferrel-Larkin-Ovchinnikov state is under hot debate. Here we report the resistivity and thermal conductivity study of a newly discovered heavy-fermion superconductor Ce2PdIn8 down to 50 mK. We find an unusual field-induced quantum critical point at the upper critical field Hc2 and unconventional nodal superconductivity in Ce2PdIn8. The jump of thermal conductivity k(H)/T near Hc2 suggests a first-order-like phase transition at low temperatures. These results mimic the features of the Q phase in CeCoIn5, implying that Ce2PdIn8 is another promising compound to investigate the exotic Q phase and FFLO state. The comparison between CeCoIn5 and Ce2PdIn8 may help to clarify the origin of the Q phase.
