Dynamics of Complex Systems probed through Tunneling Phenomena.

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The aim of this research was to investigate various "complex" systems which could be studied through any possible tunneling phenomena, either rotational or positional. The systems that we originally thought were limited strictly to (1) the ones in which the molecular interactions are non-linear, (2) those being in non-equilibrium, and (3) those involving an order-disorder nature. The idea was that the heat capacity isvery sensitive to obtain the general scheme and, in principle, the incoherent neutron inelastic scattering can determine the detail of the energy scheme.A new calorimeter system has been constructed by installing it in a ^3He-^4He dilution refrigerator. A new measurement system with an a.c. resistance bridge was also introduced. They both together allowed us to measure the heat capacity down to 0.2 K with a reasonable accuracy. To investigate the dynamical aspects of the systems, neutron scattering experiments were performed at Institut Laue Langevin at Gronoble in France and at Ratherford Appleton Laboratory in Britain.The systems studied include (1) deuteration-induced phase transitions, (2) tunneling of protons/deuterons in hydrogen bonded crystals, (3) low-energy excitations in some pressure-densified silica glass, (4) low-energy excitations in some quasi-crystals, and so on. Other complex systems, which may not involve any tunneling phenomenon, were also investigated in the last year for this project. The adsorbed monolayers at gas-solid and solid-liquid interfaces have extensively been studied.In conclusion, our next move for further research would probably be to investigate the system from the molecular level in addition to the view point of recognizing the system as a condensed phase. Those two approaches must be complementary to achieve our final goal, i.e. understanding of the overall nature of those complex systems.