AbstractsPhysics

At low temperatures submicron-size structures may exhibit certain distinctive quantum features. These include, e.g., quantum interference effects, many-body correlation effects and different collective phenomena. At the borderline of the microscopic and macroscopic world resides a regime which is called mesoscopic. Mesoscopic systems are small enough to exhibit quantum coherent behavior, yet they contain a sufficiently large number of particles to allow a statistical description. Mesoscopic conductors may be considered as a realistic platform for information processing and future nanoelectronics since they allow for scalability and integration to larger circuits. The charge transfers through disordered mesoscopic conductors exhibit different kinds of variations referred as mesoscopic fluctuations, e.g., noise, universal conductance fluctuations, and higher-order fluctuations. Containing information on the physics of the transport phenomenon not contained in conductance, these phenomena provide a delicate way to probe quantum coherence in disordered structures. Moreover, mesoscopic fluctuations can be used as a test bench for conventional condensed matter theories. In this Thesis, mesoscopic fluctuations are studied in order to extend the existing theories for the fluctuation point of view, for example, for the superconducting proximity effect, reflectionless tunneling, and weak localization. When a normal metal is in contact with a superconductor, the superconducting proximity effect induces coherent correlations of electrons and holes in the former. Studying shot noise indicates that, in addition, the proximity effect induces anticorrelations between different electron-hole pairs in a normal metal. In this Thesis, for example, noise correlations in phase coherent normal-superconducting structures are investigated. In normal metals, weak localization behavior is considered. For example, a novel scaling relation for cumulants characterizing conductance fluctuations is found. The quantum coherent phenomena considered in this Thesis have been studied by using three different kinds of theoretical approaches: the quasiclassical Keldysh Green's function formalism, the random matrix theory, and a numerical scattering approach. Matalissa lämpötiloissa riittävän pienten rakenteiden kvanttimekaaniset koherentit ominaisuudet nousevat esiin. Tällaisia ovat esimerkiksi kvantti-interferenssi-, monihiukkas- ja erilaiset kollektiiviset ilmiöt. Mikroskooppisen ja makroskooppisen maailman välissä sijaitsee mesoskooppiseksi kutsuttu alue. Mesoskooppiset systeemit ovat tarpeeksi pieniä, jotta kvanttikoherentteja ilmiötä voi esiintyä. Toisaalta ne sisältävät riittävästi hiukkasia tilastollisen kuvauksen kannalta. Mesoskooppisten johteiden voidaan odottaa soveltuvan tulevaisuuden nanoelektroniikan käyttöön, sillä niistä koostuvia komponentteja on mahdollista liittää yhteen suuremmiksi virtapiireiksi. Epäjärjestyneissä mesoskooppisissa johteissa kuljetusilmiöitä kuvaavat suureet vaihtelevat aika- ja ensemble-keskiarvojensa…