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Free keywords:
double quantum dot; single electron tunneling; delocalization; molecular states
Abstract:
Semiconductor quantum dots, so-called artificial atoms, have attracted
considerable interest as mesoscopic model systems and prospective
building blocks of the "quantum computer". Electrons are trapped
locally in quantum dots, forming controllable and coherent mesoscopic
atom- and moleculelike systems. Electrostatic definition of quantum
dots by use of top gates on a GaAs/AlGaAs heterostructure allows wide
variation of the potential in the underlying two-dimensional electron
gas. By distorting the trapping potential of a single quantum dot, a
strongly tunnel-coupled double quantum dot can be defined. Transport
spectroscopy measurements on such a system charged with N = 0, 1, 2....
electrons are presented. In particular, the tunnel splitting of the
double well potential for up to one trapped electron is unambiguously
identified. It becomes visible as a pronounced level anticrossing at
finite source drain voltage. A magnetic field perpendicular to the
two-dimensional electron gas also modulates the orbital excitation
energies in each individual dot. By tuning the asymmetry of the double
well potential at finite magnetic field the chemical potentials of an
excited state of one of the quantum dots and the ground state of the
other quantum dot can be aligned, resulting in a second level
anticrossing with a larger tunnel splitting. In addition, data on the
two-electron transport spectrum are presented. (c) 2006 Elsevier B.V.
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