Singlet-triplet oscillations and far-infrared spectrum of four-minima quantum-dot molecule

TL;DR

This study investigates the ground states and far-infrared spectra of two electrons in a four-minima quantum-dot molecule under magnetic fields, revealing how symmetry, electron interactions, and magnetic effects influence spectral features.

Contribution

It provides a detailed analysis of how low-symmetry confinement and electron interactions affect the FIR spectra and ground state transitions in a four-minima quantum-dot molecule.

Findings

Ground states alternate between singlet and triplet with magnetic field.

Discontinuities in FIR spectra occur at ground state crossings.

Non-circular symmetry causes anticrossings and additional spectral modes.

Abstract

We study ground states and far-infrared spectra (FIR) of two electrons in four-minima quantum-dot molecule in magnetic field by exact diagonalization. Ground states consist of altering singlet and triplet states, whose frequency, as a function of magnetic field, increases with increasing dot-dot separation. When the Zeeman energy is included, only the two first singlet states remain as ground states. In the FIR spectra, we observe discontinuities due to crossing ground states. Non-circular symmetry induces anticrossings, and also an additional mode above $\omega_+$ in the spin-triplet spectrum. In particular, we conclude that electron-electron interactions cause only minor changes to the FIR spectra and deviations from the Kohn modes result from the low-symmetry confinement potential.