Complex System In The Phase Transition Phenomenon

Chapter 1: Through our study on Cicada Cryptotympana atrata, we observed that the acoustic synchrony evolves with the colony population. This finding is not clarified in the literature. We build a model based on Winfree's theory and reproduced the dynamics. With increasing the number of oscillators, the coherence emerges beyond a threshold in population. In comparison, we notice that coherence in chemical oscillators and many clapping hands rely on coupling strength and clapping frequency dispersion as their control parameter, respectively. Our work offers a chance to get better understanding of the spontaneous ordering phenomenon and phase transitions in complex systems.Chapter 2: Two dimensional electronic systems NaCoO2 provide us a new approach that we should study the relationship between superconductivity and low-dimensional ion-conduction channel. LiTi2-xVxO4, both as a superconductor and an ion-conductor become our object of study. We succeeded in making the best quality sample ever and performed systematic transport measurement. The result reveals large interplay of superconductivity and heavy-fermions-like magnetism, which broke former assumptions to some extent. Further works suggest the importance of ion-transport inside a superconductor like NaCoO2 .Chapter 3: The transition metal chalcogenides have long been material systems of scientific focus, for example both NbSe2 and MoS2 in 1970's and TiS2 and TiSe2 in 1980's brought us significant problem to think. This chapter aims to study a kind of chalcogenides, NiS2-xSex systems with multiple-phase and multiple-freedom of electrons. By transport and photoemission measurement, we found a crucial phenomenon, called quantum critical phenomena. Further comparison of doping and temperature dependent date, we obtain the electron behaviors near the quantum critical point and the quantum ground state.