Origin of non-superconducting phase by which the superconducting phase were divided.

层状钴氧化物的超导性表现在T-v_Q（或-晶格参数c）相图中，其中v_Q为Co核电子四极共振频率。在此相图中，非超导相（SC）似乎将SC相分为两个区域。为了研究非sc相的性质，我们测量了各种物理性质的t依赖性。结果一致地被非sc相理解为不处于磁性有序状态，而是处于电荷不成比例状态。虽然可以通过层状氧化钴的a_<1g>-带和e_g -带之间的相对能级变化来解释多sc相和非sc相的存在，但我们发现这些结果排除了这种可能性，例如电子比热系数的v_Q（或c）依赖性，核磁共振骑士位移，以及中子散射测量的磁激发的q依赖性。由于非磁性杂质不抑制超导性，且NMR Knight位移支持自旋-单重态对的形成，因此认为SC对主要是由电子-声子相互作用形成的，认为向非SC相的转变是通过费米能级态密度的降低抑制了超导性。接下来，我们研究了层状钴氧化物的铁基超导体，其T_c是其十倍。发现Fe体系和co -氧化物对T_c的非磁性杂质影响非常弱，表明Fe体系为与层状钴氧化物进行比较研究提供了机会。

The superconductivity of the layered cobalt oxides appears in the phase diagram of T-v_Q (or -the lattice parameter c), where the v_Q is Co nuclear electronic quadrupole resonance frequency. In this phase diagram, the non-superconducting (SC) phase appears to divide the SC phase into two regions. To investigate the nature of the non-SC phase, we have measured the T-dependences of various physical properties. The results are consistently understood by the non-SC phase to be not in the magnetic ordered state but in the charge disproportionate state. Although the existences of multi-SC phases and non-SC phase were explained by changing of the relative energy level between a_<1g>-band and e_g'-band of this layered cobalt oxide, we found that the possibility was excluded by those results, for example, the v_Q (or c) dependence of the electronic specific heat coefficient, NMR Knight shift, and the q-dependence of magnetic excitation by neutron scattering measurements. As the non-magnetic impurity does not suppressed the superconductivity, and NMR Knight shift supports the spin-singlet pairing formation, the SC pairing is considered to be formed mainly by electron-phonon interaction, and it is considered that the transition to non-SC phase suppresses the superconductivity though the decreases of the density of states at Fermi level.Next, we have studied the Fe-based superconductors with ten times as large as T_c for the layered cobalt oxides. Non-magnetic impurity effect on T_c for Fe system was found to be very weak as well as the Co-oxides, indicating that the Fe system is found to give an opportunity to perform comparative studies with the layered cobalt oxides.