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Ultrasmall systems called quantum dots (QDs) and single-electron transistors, where Coulomb interaction (Coulomb blockade) plays an important role, are very interesting and promising devices, which allow for control and manipulation of a single spin. With quantum dots, due to the control of a single electron charge, the possibility for manipulation of a single spin is opened up, which can be important for spintronics and quantum computing. On the level of a few spins, the new physics related to exchange interaction, spin blockade, Larmor precession, electron spin resonance (ESR), the Kondo effect, and hyperfine interactions with nuclear spins is raised. Also combining ferromagnetic materials with QDs opens up a new possibility of control and manipulation of a QD single spin by direct exchange interactions and construction of ferromagnetic single-electron transistors (F-SET).

This chapter discusses the phenomenon of Coulomb blockade, which takes place in small junctions. It first explains conditions of observing Coulomb blockade in single- or multiple junction systems and then details the orthodox theory of single-electron tunnelling, which consists of calculating the tunnelling rates and using them in a master equation for the charge states. This theory allows understanding of the properties of a single-electron transistor. The higher-order cotunneling is explained briefly. The phenomenon of dynamical Coulomb blockade arising in single junctions placed in high-resistance environments is discussed in detail. The chapter closes by describing main single-electron devices besides the conventional single-electron transistor: Coulomb blockade thermometer, radio frequency single-electron transistor, and a single electron pump.

After brief review of important electrical transport measurements, optical and Raman methods, techniques of angle-resolved photoemission spectroscopy (ARPES) and scanning tunnelling microscopy, spectroscopy (STM/STS) and scanning tunneling potentiometry are introduced. It is pointed out that ARPES, like conventional transport measurements, average over a large area, while STM and scanning single electron transistor (SSET) measurements are local, on an atomic scale in some cases. Capacitance spectroscopy is described and the scanning single electron transistor is described as a method of mapping surface potential and determining a density-of-states quantity called the inverse compressibility. The use of the latter SSET method in finding fractional quantum Hall effects is described.