Few-electron quantum dots

TLDR

Three energy scales are distinguished: discrete single‑particle states from confinement, direct Coulomb interaction between charges on the dot, and exchange interaction between parallel‑spin electrons. The study reviews electron‑transport experiments on few‑electron vertical quantum‑dot devices and discusses interactions among 1–20 electrons using simple models. The authors employ current–voltage and gate‑voltage spectroscopy, magnetic‑field‑induced reorganization of electron occupation, and simple interaction models to probe the energy scales in few‑electron quantum dots. The simple models consistently reproduce a wide range of experiments, revealing atomic‑like shell structure, Hund’s rule, and spin singlet/triplet states, while the high experimental control allows systematic exploration of artificial elements by adding electrons via gate voltage.

Abstract

We review some electron transport experiments on few-electron, vertical quantum dot devices. The measurement of current versus source-drain voltage and gate voltage is used as a spectroscopic tool to investigate the energy characteristics of interacting electrons confined to a small region in a semiconducting material. Three energy scales are distinguished: the single-particle states, which are discrete due to the confinement involved; the direct Coulomb interaction between electron charges on the dot; and the exchange interaction between electrons with parallel spins. To disentangle these energies, a magnetic field is used to reorganize the occupation of electrons over the single-particle states and to induce changes in the spin states. We discuss the interactions between small numbers of electrons (between 1 and 20) using the simplest possible models. Nevertheless, these models consistently describe a large set of experiments. Some of the observations resemble similar phenomena in atomic physics, such as shell structure and periodic table characteristics, Hund's rule, and spin singlet and triplet states. The experimental control, however, is much larger than for atoms: with one device all the artificial elements can be studied by adding electrons to the quantum dot when changing the gate voltage.