Four-electron shell structures and an interacting two-electron system in carbon nanotube quantum dots

TL;DR

This study investigates four-electron shell filling and spin interactions in carbon nanotube quantum dots through low-temperature transport measurements, revealing Zeeman splitting, spin flips, and Hund's rule effects.

Contribution

It provides the first detailed observation of four-electron shell filling, spin polarization, and exchange interactions in carbon nanotube quantum dots, highlighting their analogy to artificial helium atoms.

Findings

Observed four-electron shell filling in nanotube quantum dots.

Detected Zeeman splitting and spin flip phenomena.

Demonstrated singlet and triplet states with exchange splitting.

Abstract

Low-temperature transport measurements have been carried out on single-wall carbon nanotube quantum dots in a weakly coupled regime in magnetic fields up to 8 Tesla. Four-electron shell filling was observed, and the magnetic field evolution of each Coulomb peak was investigated, in which magnetic field induced spin flip and resulting spin polarization were observed. Excitation spectroscopy measurements have revealed Zeeman splitting of single particle states for one electron in the shell, and demonstrated singlet and triplet states with direct observation of the exchange splitting at zero-magnetic field for two electrons in the shell, the simplest example of the Hund's rule. The latter indicates the direct analogy to an artificial He atom.