Marc A. Kastner

My early research was on the electronic and optical properties of amorphous semiconductors, especially chalcogenide glasses. Although the atoms in these materials are not arrayed on a crystal lattice, they are still useful for electronic and optical memories. Together with David Adler and Hellmut Fritzshe, I invented a model that relates the electronic properties of these materials to their chemical bonding. For a number of years I studied the physics of high temperature superconductors, in collaboration with Robert Birgeneau, particularly the relationship of their unusual magnetic properties to their electron transport. In 1990 my group fabricated the first semiconductor single-electron transistor, a transistor that turns on and off again every time one electron is added to it. My group used these nano-electronic devices as tools to study the quantum mechanical behavior of electrons confined to nanometer dimensions. In particular, in 1998 we discovered the Kondo effect, a state in which electrons inside and outside the transistor are quantum mechanically entangled with each other. We were able to study the Kondo effect out of equilibrium, which was not possible in other Kondo systems. Most recently we have been studying one of the most unusual of the quantum Hall states, that for which the filling fraction is 5/2. Using tunneling in nano-structures we have been able to measure the fractional charge and coupling constant for the quasiparticles in this state.