| Research Abstract |
Evolution of the gigantic effects was attempted by the control of quantum fluctuations both in dielectrics and paramagnetics. Finally, gigantic quantum effect was found, for the first time, in quantum paraelectric SrTiO_3, KTaO_3, and CaTiO_3. Also metal-insulator transition due to spin crossover was successfully found in cobalt perovskite. These two results are quite important in the solid state physics and many researchers are following our experiments.
The key points are summarized as follows.
1. Oxygen isotope exchange induces a transition from quantum paraelectric to quantum ferroelectric. Quite large voltage dependence appears in the vicinity of critical composition of 33 % exchange. Ferroelectric soft mode was found for the first time by the hyper-Raman scattering. Small bias and irradiation of UV light for the Quantum paraelectrics, SrTiO_3, KTaO_3, and CaTiO_3, induces a new quantum state, which gives a gigantic dielectric constant.
2. Spin crossover in cobalt ions was successfully controlled by the charge and orbital ordering in perovskite-type oxides. The phase transition due to the spin crossover was found to be first order-type, accompanying a large volume change, a metal-insulator transition, and a paraelectric-nonmagnetic transition. This is the first example of the spin crossover in perovskites.
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