StatusThe thesis was presented on the 5 December, 2005
Approved by NCAA on the 26 January, 2006
Abstract– 0.28 Mb / in romanian
This thesis highlights the investigation of quantum oscillation effects in bicrystals of Bi and Bi-Sb alloys with different angles of disorientation of crystallites. The majority of researches have been performed at helium temperatures and in magnetic fields up to 45T.
It has been determined that in Bi bicrystals with small angles of disorientation the quantum interference nature of interaction between charge carriers and the crystallite interface (CI) becomes considerable. With the Increase of a crystallite disorientation angle, the CI structure as well as the amplitude and harmonics of oscillation tend to change.
The crystallite interface of a twisted type in bicrystals of Bi and Bi-Sb alloys consists of central part (width of layer Lc = 70÷90 nm) and two conjugated layers (common width of these layers LL = 170÷250 nm).
In Bi bicrystals with large angles of crystallite disorientation and the CI of a twisted type, two superconducting phases have been revealed, one of them equaling Tc1 ~ 8.4K and the other being Tc2 ~ 4.3K. The phase with the critical temperature Tc1 ~ 8.4K is localized in the central part of the crystallite interface, whereas the one with Tc2 ~ 4.3K in the adjoining layers. It has been discovered that bicrystals magnetic properties are considerably different from those of Bi monocrystals. There is magnetic susceptibility in weak fields.
The field dependences of the magnetic moment M(H) are characterized by marked diamagnetism in weak fields, a paramagnetic maximum (in the area of magnetic fields, 0.5-2.0 kOe), weak dependence on temperature and linear variation at H > 2 kOe.
In the bicrystals of Bi-Sb alloys, is revealed a new type of quantum oscillations which are explained by the rotation of the electronic part of Fermi surface.
Under consideration  :