ABSTRACT
Semiconductor nanostructures and mesoscopic electronic devices based on a two-dimensional electron gas (2DEG) have been a focus of attention for the semiconductor community during the past few decades. is is due to the new fundamental physics that these structures exhibit, and also due to possible applications in future electronic devices and devices for quantum information processing. A quantum point contact (QPC) represents the cornerstone of the mesoscopic physics. is is not only because the QPC is the simplest mesoscopic device, but also because most of the mesoscopic devices contain the QPC as their integral part. is has apparently motivated a strong interest in the various aspects of the electronic and transport properties of the QPC. In fact, one of the most important discoveries that gave a strong momentum to the whole eld of mesoscopic physics was the discovery of the conductance quantization of the QPC in 1988 (van Wees et al., 1988; Wharam et al., 1988). Studies of the conductance quantization in the QPC provided valuable information not only on the fundamentals of the phase-coherent electron motion in low-dimensional structures, but also outlined important material aspects (such as the e ect of impurities, potential con nement, etc.). e QPC has also proven to be the key system for studying the various aspects of the quantum Hall physics. is applies both to the pioneering studies in the beginning of the “mesoscopic era” in the early 1990s focusing on the basic aspects of the subband depopulation as well as to more recent studies of the fractional Hall regime revealing the exotic
features of interacting electrons in a high magnetic eld such as fractional statistics and charge. It is also important to mention that apart from strong fundamental interest, a QPC found its important practical application as a noninvasive voltage probe and a single-electron charge detector. By now, many features of the electronic and transport properties of the QPC are well understood. However, even 20 years a er the discovery of the conductance quantization, some of the important aspects of the QPC conductance still represent topics at the forefront of research and lively debates, where the emphasis is shi ed to aspects of the electron interaction, spin, and nonequilibrium e ects.
