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

层状钴氧化物的超导电性出现在T-v_q(或晶格参数c)的相图中，其中v_q是钴的核电子四极共振频率。在这个相图中，非超导(Sc)相似乎将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依赖关系。结果一致地被非Sc相理解为不处于磁有序状态，而是处于电荷不成比例状态。虽然通过改变层状钴氧化物的a&lt；1g&gt；-带和e_g‘-带之间的相对能级来解释多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，核磁共振奈特移，以及通过中子散射测量的磁激发的q依赖。由于非磁性杂质不会抑制超导电性，而核磁共振奈特位移支持自旋-单重态配对的形成，因此认为Sc配对主要是由电子-声子相互作用形成的，并认为向非Sc相的转变通过费米能级的态密度降低而抑制了超导电性。Fe系和Co氧化物的非磁性杂质对T_c的影响都很弱，表明Fe系提供了与层状钴氧化物进行比较研究的机会。

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.