Electrical Properties of Quantum Dot Systems
Quantum dots, also denoted as artifical atoms or zero-dimensional electron systems, are objects where few to many electrons are confined in a small spatial enclosure of mesoscopic size (few tens to few hundreds of nanometers), allowing a single electron only certain eigenvalues for its energy (‘quantum mechanical particle in a box’).
Quantum dots weakly linked to leads (‘source’ and ‘drain’) by quantum mechanical tunneling through energy barriers can be considered as model systems to study fundamental aspects of electrical transport through single atoms or molecules. Especially the number of electrons confined on the quantum dot can be controlled electrostatically by nearby gate electrodes.
Quantum dot systems can be designed to purpose since they are usually fabricated by conventional semiconductor growth and processing technology. Drawback of their mesoscopic size is that exploring their electrical properties requires low temperature (below 0.1 Kelvin).
Coulomb blockade and single-electron charging are observed in electrical transport as a consequence of the repelling electrostatic electron-electron interaction in quantum dots. Such quantum dot systems behave as single-electron transistors.
However, the degree of freedom in occupying the quantum dot either with the electron spin orientation up or down can cause with lowering the temperature a peculiar quantum dynamics, overcoming the Coulomb blockade of the quantum dot system. The effect can be described in the framework of Kondo physics.
Astonishingly at first view, even the arrangement of two quantum dot systems – interacting purely electrostatically – can behave as a pseudo-spin Kondo system.