Mechanism and novel functions of pressure-induced superconductor-insulator transition in chalcogenide spinels

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In this study, he mechanism of the pressure-induced superconductor insulator transition in chalcogenide spinel CuRh_2S_4 has been understood as the dual effects of a band degeneracy quenching bind in Yb-metal and a novel charge ordering found in CuIr_2S_4. The change in transport property around room temperature from metallic to semimetallic one is due to the band degeneracy Quenching. The tranpcat ptherty . change below T* is due to the charge ordering. Using a novel function of the pressure-induced superconductor insulator transition, we can construct a new active device. We are now preparing to apply a patentAs for a development of new materials, we have succeeded in synthesizing poly crystals of CuCrZrS_4, CuCr_2Te_4, CeMg2(Cu_<l-x>,Ni_x)_9.We have found that CuCrZrS_4 undergoes a ferromagnetic transition at 58K. However, there in no specific heat anomaly around 58K, surprisingly. This phenomenon can be due to a successive spin freezing. We have determined the crystal structure of CuCr_2Te_4, which has a cubic spinel structure with a = 11.134A. We also found for the first time that this compound undergoes a ferromagnetic transition at Tc = 324K. From the Curie-Weiss type temperature dependence of magnetic susceptibility between 380 and 650K, we obtained the effective magnetic moment of 4.14μ〓/Cr-ion and the Weiss temperature of +357K The low temperature magnetization shows Bloch's T^<3/2> and T^<5/2> law, which suggests a spin excitation. As for CeMg2(Cu_<1-x>Ni_x)_9, both compounds with x = 0 and 0.2 show remarkable specific heat anomalies at 2.5K and 1.7K, respectively. The origin for the specific heat anomalies is an antiferromagnetic transition. We also determined the crystal field spritting level scheme of 4f electron in these compound from the Schottky-type anomalies in the specific heat. As a new landscape of our study, we measured the solid state properties of a caged atom.