DEVELOPMENT OF TRANSIENT THERMOELECTRIC EFFECT IN HIGH MAGNETIC AND ELECTRIC FIELDS AND ITS APPLICATION TO THE STUDY OF CHARGE DENSITY WAVE MATERIALS

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Our newly developed technique is a "dynamical" one, called the pulsed-laser induced 'Transient Thermoelectric Effect (TTE)" method, in which after a pulsed laser is irradiated upon one end of a sample, one measures an induced voltage across both ends of the sample and analyzes its decay profile, from which we can obtain valuable information about thermal diffusions of photo-generated carriers (and phonons) drifting along the concentration and temperature gradient in the sample. This technique is particularly useful for a multicarrier system consisting of both conduction electrons and holes, -we refer to as "conduction-carrier Spectroscopy". For a more general application of this technique, we are undertaking the TTE experiments under an applied magnetic field and under a steady flow of a dc electric current to get further information about transport properties of various materials, such as quasi-two-dimensional molybdenum oxides that show a metal-semiconductor transition due to charge-density-wave instabilities. We have improved the hitherto-made TTE apparatus with the fixed laser wavelength of 1064 nm with a Nd : YAG to a variable range of 690-1320 nm using a combined laser source of Ti : Sapphire/Foresterite with the Nd : YAG source, a detectable time range from 50 ns clown to as fast as 1 ns with a digital oscilloscope, and laser intensity reduced by one tenths of the previous one as well, With this improved apparatus combined with conventional de transport techniques, we have obtained valuable information about electronic properties of CDW materials of n-Mo_4O_1_1, molecular conductors (DMe-DCCNQI)_2Cu and its duetetated salts, layered material TaS_2, as well as ultrapure compensated metal of tungsten, synthetic diamond films, and Perovskite manganites. In addition, high magnetic field transport and linear and nonlinear response to a pulsed electric field were also studied.