Nouvelles possibilités d'étude d'un milieu très réfléchissant dans l'infrarouge lointain : application aux nouveaux supraconducteurs à haute température critique

Abstract : This work started four years after the discovery of High Tc superconductors, when it has been possible to get single crystals plates thin enough and stable enough to permit transmissions studies in the 10 - 40 cm[ exponent -1] spectral range of the far infrared. They were thin layers 200 A to 500 A thick deposited on MgO single crystals. lt has been necessary first to characterize MgO as accurately as possible. Then we had to find methods to get transmission, reflectivity, and absorption for high absorbing stratified samples. The last and best results have been obtained with a grid spectrometer and a cryostat especially made for submillimeter waves and a new interferometric method. We have been able to get the free-carriers plasma frequency from 4 K to 300 K and also the collision frequency of quasiparticles. It has been shown that the number of quasiparticles is given by a ([thêta]/{thêta index c]) [exponent 1.5] law rather than a more conventional ([thêta]/[thêta index c])[exponent 4], [thêta] being the temperature of the sample. Lasses in the microwaves at low temperatures are due mainly to the small number of residual quasiparticles, whereas in the far infrared they are mostly ascribed to the low frequency wing of the infrared oscillators that we have to introduce into the mode!. More accurate results are expected in the near future.
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Masato Tazawa. Nouvelles possibilités d'étude d'un milieu très réfléchissant dans l'infrarouge lointain : application aux nouveaux supraconducteurs à haute température critique. Autre [cond-mat.other]. Université Henri Poincaré - Nancy 1, 1995. Français. ⟨NNT : 1995NAN10401⟩. ⟨tel-01748620⟩

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