Electronic phase competition and valence states in quasi-one-dimensional halogen-bridged metal complexes

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Quasi-one-dimensional halogen-bridged metal complexes (MX chains) have been studied extensively because the MX chains have various electronic phases such as spin density wave (SDW), charge density wave (CDW) etc. Moreover, nonlinear excitations such as polaron are created in the MX chains, as in conducting polymers. We have demonstrated that electron spin resonance (ESR) is a useful method to detect magnetic ions (M^<3+>) in the MX chains ; however the above measurements have been limited for static studies so far. The aim of the present research is to construct time-resolved photoexcited ESR system, and then to apply the ESR system for detecting the excitations in the MX chains and studying the photo control of the competing two electronic phases.First, we have constructed the time-resolved photoexcited ESR system and performed the studies of the excitations in the MX chains having CDW ground state. In Pd_2(chxn)Br_3 we have successfully observed LESR signals due to photogenerated spi … More ns at low temperatures ; time of the transient response of LESR is of the order of several to several ten minutes depending on temperature. We have also studied the dependence of LESR on the excitation-light intensity and excitation spectrum of LESR, and then found that soliton excitation is dominant for the photoexcited spins by analyzing the above results. In [Pt(en)_2][Pt(en)_2X_2](ClO_4)_4(X=Cl and I), we have successfully observed the excitation spectra of LESR ; these photogenerated spins are found to be solitons for X=Cl and polarons for X=I, consistent with the results of photoinduced absorption etc. Second, we have clarified the competing electronic phase of SDW and CDW, and substituent effect of halogen-ions to electronic phases by using mixed-metal MX chains Ni_<1-x>Pd_x(chxn)_2X_3 and Ni_<1-x>Co_x(chxn)_2X_3(XCl and Br). Moreover, we have studied carrier properties of the above chains by measuring resistivity and thermoelectric power using single crystals under pressure. Furthermore, more developed form of the MX chains, MMX chains have been measured by ESR. We have firstly detected an averaged valence and CDW phases, and soliton excitation in an alternate charge polarization phase in the MMX chains. Less