Electronic States in Silicon Quantum Dots: Multivalley Artificial Atoms

TL;DR

This theoretical study explores how multivalley structures in silicon quantum dots influence electronic states, revealing effects on spin configurations, valley occupation, and the impact of size and intervalley scattering.

Contribution

It provides new insights into the electronic and spin states of silicon quantum dots considering multivalley effects, which were not thoroughly analyzed before.

Findings

Electrons in different valleys occupy lowest levels without Hund's coupling in small dots.

High-spin states can be achieved with small magnetic fields.

Intervalley scattering splits degenerate levels, affecting spin states.

Abstract

Electronic states in silicon quantum dots are examined theoretically, taking into account a multivalley structure of the conduction band. We find that (i) exchange interaction hardly works between electrons in different valleys. In consequence electrons occupy the lowest level in different valleys in the absence of Hund's coupling when the dot size is less than 10 nm. High-spin states are easily realized by applying a small magnetic field. (ii) When the dot size is much larger, the electron-electron interaction becomes relevant in determining the electronic states. Electrons are accommodated in a valley, making the highest spin, to gain the exchange energy. (iii) In the presence of intervalley scattering, degenerate levels in different valleys are split. This could result in low-spin states. These spin states in multivalley artificial atoms can be observed by looking at the magnetic-field dependence of peak positions in the Coulomb oscillation.