Abstract
To realize the probability of nanodevices application using quantum phase information, dephasing processes are one of the most crucial essential issues regarding semiconducting mesoscopic systems. This thesis presents a series of experiments that study the phase coherence and dephasing mechanisms by using Aharonov–Bohm (AB) and spin-type Mach–Zehnder interferometers (SMZIs) fabricated in GaAs/AlGaAs heterostructured crystals. In chapter 1, we introduce the motivation and context for the experimental works described in the following chapters. In chapter 2, we investigate the dependence of the dephasing rate in a ballistic AB ring on the temperature, bias current, and probe configuration. First, we would like to study how the probe configuration influences the conductance and the dephasing rate. In fact, averaging of the transmission phase, in which current is carried by thermally excited or current-induced electrons, results in dephasing. We find that the appropriate energy window for dephasing is set by the drift velocity of the interfering electrons and the asymmetry of the ring path. In chapter 3, we investigate the dephasing rates in ballistic AB rings with local and nonlocal probe configurations by tuning the transmission through one arm of the ring. The dephasing rates are independent of the probe configuration, whereas the transmission through the ring paths is equal. In contrast, because AB interferometers are tuned to be strongly asymmetric, the dephasing rate of the local configuration becomes larger than that of the nonlocal configuration. We find that our observations can be explained qualitatively by voltage fluctuations from the measurement circuit, as proposed by G. Seelig, S. Pilgram, A. N. Jordan, and M. Büttiker [56]. In chapter 4, we first introduce a novel SMZI by using spin-resolved edge states in the integer quantum Hall regime. Furthermore, to investigate the phase coherence length in this interferometer, we determined the finite temperature coherence length of the spin-resolved edge states by designing interferometers of various sizes and attempted to explain the dephasing mechanism in this novel system. The phase coherence length in the present experiment, surprisingly, is noticeable larger than the charge coherence length found in an electronic MZI[75, 83]. Finally, in chapter 5, we summarize our finding from the experimental works and discuss future work based on our presented results.