京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22876号 / 理博第4642号 / 新制||理||1667(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 寺西 利治, 教授 島川 祐一, 教授 長谷川 健 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Toxic singlet oxygen can be populated by the quenching of triplet states of chlorophyll (Chl). In photosynthetic light-harvesting complexes (LHCs), the gen- eration of singlet oxygen is prevented by a photoprotective mechanism based on an energy transfer from Chl triplets to carotenoids, which occurs via a Dexter mechanism (DET). The temperature dependence of the DET was studied in three selected LHCs by means of transient absorption spectroscopy. The emphasis was on a chlorophyll a-chlorophyll c2-peridinin-protein complex (acpPC) of Dinoflagel- late Amphidinium carterae. The results obtained from acpPC were compared with those for LHC-II from pea and chlorosomes of Chloroflexus aurantiacus. All three antennas exhibit high efficiency and fast rate of chlorophyll triplet quenching by carotenoids at room temperature, which prevents the accumulation of Chl triplets. The fast rate of quenching persists at low temperatures (≥77 K) in the case of LHC-II. However, the efficiency of the Chl triplets quenching is lower as proved by a detection of long-lived Chl triplets with a millisecond lifetime. These triplets were assigned to peripheral Chls that are not neighbouring with carotenoids active at 77 K. A similar population of long-lived Chl triplets was detected in the acpPC complex. In acpPC, the rate of the...

Chlorophyll molecules in their triplet excited state can react with the ground state oxygen, producing oxygen in a singlet excited state, which is very reactive and thus very harmful to the light-harvesting complex. Photosynthetic organisms employ carotenoids to prevent the damage by quenching both excited (singlet) states of oxygen and excited triplet states of chlorophyll. In this work, we use ns transient absorption spectroscopy and global analysis to study the dynamics of carotenoid and chlorophyll triplet states in two light-harvesting complexes of Amphidinium carterae, the Peridinin-Chlorophyll a-Protein complex (PCP) and the main light-harvesting complex (LHCP). It appears that at room temperature all triplets are transferred from chlorophylls to carotenoids within ~ 5 ns, providing a very efficient protection against formation of singlet oxygen. One carotenoid triplet with a lifetime of ~ 10.2 µs participating in the chlorophyll triplet quenching was observed in the PCP sample, while results from LHCP suggest that two carotenoid triplets with a similar lifetime of ~ 2.5 µs contribute to quenching of chlorophyll triplet states. The two carotenoid triplets are attributed to peridinin placed in a polar environment and peridinin placed in a non-polar environment in the LHCP complex.

Les systèmes hybrides supraconducteur-ferromagnétique présentent souvent de nouveaux phénomènes physiques, et pourraient également être utiles pour concevoir de nouvelles mémoires non-volatiles et haute densité pour les circuits supraconducteurs. Cette thèse étudie deux types différents d'hybrides SF, chacun suivant une approche possible de dispositif mémoire, en se focalisant sur les aspects fondamentaux. L'un porte sur l'effet de proximité dans des hétérostructures d'oxydes. Dans celles-ci, des corrélations triplet apparaissent, qui sont à la fois supraconductrices et polarisées en spin. Elles permettraient d'utiliser des effets de la spintronique comme la GMR, mais sont également très sensibles aux propriétés d'interface. Nous les avons étudiées dans des tricouches SFS d'oxydes, par des mesures de conductance. Celles-ci montrent des oscillations, en partie liées à ces états triplets. Nous observons également que les effets d'interface affectent les propriétés électroniques du ferromagnetique, en particulier lorsque cette couche est mince. Un autre genre d'interaction se produit par les champs de fuite provenant des structures de domaines. Des propositions théoriques récentes ont suggéré que de petites structures en tourbillon appelées skyrmion peuvent interagir avec la supraconductivité par ce mécanisme. Nous avons étudié ce couplage dans des bicouches, dans lesquelles les propriétés de transport sont dominées par la dynamique des vortex supraconducteurs. Nous avons vu une augmentation du courant critique en présence de skyrmions comme de domaines. Celles-ci créent également un effet Hall inhabituel dans l'état supraconducteur. La plupart de ces propriétés peuvent être expliquées qualitativement par la dynamique et le mouvement guidé des vortex. / Superconductor-ferromagnet hybrid systems often bring about new physics and may as well be useful to design new non-volatile, high-density memory devices for superconducting electronics.In this thesis, we study two different types of SF hybrids, each following a possible approach to memory devices, but focusing on fundamental aspects. One is about the proximity effect in oxide heterostructures. In these, triplet correlations appear, that are both superconducting and spin-polarized. These enable using effects from spintronics like GMR, but are also very dependent on interface properties. We investigated these in SFS oxide trilayers by conductance measurements. These showed oscillations which may, in part, be related to these triplet states. We also observed that interface effects affect the electronic properties of the ferromagnet, especially when that layer is thin. Another type of interaction occurs through stray magnetic fields from the domain structures. Recent theoretical proposals suggested that small swirling spin textures called skyrmions could similarly interact with superconductivity through this mechanism. We investigated such coupling in bilayers, in which the superconducting vortex dynamics dominate the transport properties. We found that the presence of skyrmions and domains alike enhances the critical current. It also leads to an unusual Hall effect in the superconducting state. Most of these properties can be explained qualitatively in terms of vortex pinning and guided motion.