Role of spin-orbit interaction and Berry's phase in Aharonov-Bohm oscillations.

摘要

In this thesis we report the results of study on the role of spin-orbit (SO) interaction in Aharonov-Bohm (A-B) oscillations measured in (311)A GaAs two-dimensional (2D) holes, and the observed novel structures in the Fourier transform (FT) spectra of the A-B oscillations, which we interpret as manifestation of Berry's phase and interference of spin states.; In the FT spectra of A-B oscillations measured in GaAs 2D holes, we observed novel structures, which are more complex than what is observed in the A-B measurements done in other materials (e.g., normal-metals and GaAs 2D electrons). To interpret the experimental data, we develop a simple model which considers A-B effect in a system with strong SO interaction. Using parameters such as spin-splitting energy (ΔE), splitting of the Fermi wavevector (Δk), and the effective magnetic field ( B_eff), which characterize spin-related properties in GaAs 2D holes, we are able to obtain a qualitatively good agreement between simulations based on this model and experimental results. In addition, through further analysis of experimental data and careful comparison with simulated results, we demonstrate that observation of these novel features in GaAs 2D hole rings is indeed evidence for Berry's phase. Furthermore, it suggests that GaAs 2D hole is an excellent candidate for studying phenomena caused by spins.; Moreover, the simple model mentioned above suggests a periodic evolution of A-B oscillations with Δk, which can be tuned by changing the front gate voltage V_FG. In the magnetoresistance of the ring, as V_FG is tuned, we observe changes in the FT spectra. These changes can be systematically tracked in terms of simplicity and complexity in the FT structures as a function of V _FG.; Finally, to study the phase coherence of hole transport in our mesoscopic ring, we measured the temperature dependence of the A-B oscillations. We found that the average oscillation amplitude exhibits a temperature dependence of exp[-L/L_&phis;(T)], which represents the dephasing related to the phase coherence length L _&phis; with L_&phis;(T) ∼ 1.5 T−1 μm.