Ground state and optical conductivity of interacting polarons in a quantum dot

TL;DR

This paper investigates the ground state energies and optical properties of interacting polarons in quantum dots, revealing spin state transitions influenced by electron density and coupling strength, with implications for experimental optical spectra.

Contribution

It introduces a path integral approach for fermionic polarons in quantum dots and analyzes spin transitions and energy states as functions of system parameters.

Findings

Identification of three possible spin states for polarons in quantum dots.

Observation of spin transition from Hund's rule to spin polarization with decreasing density.

Prediction of observable optical spectrum changes due to spin state transitions.

Abstract

The ground-state energy, the addition energies and the optical absorption spectra are derived for interacting polarons in parabolic quantum dots in three and two dimensions. A path integral formalism for identical particles is used in order to take into account the fermion statistics. The approach is applied to both closed-shell and open-shell systems of interacting polarons. Using a generalization of the Jensen-Feynman variational principle, the ground-state energy of a confined N-polaron system is analyzed as a function of N and of the electron-phonon coupling constant. As distinct from the few-electron systems without the electron-phonon interaction, three types of spin polarization are possible for the ground state of the few-polaron systems: (i) a spin-polarized state, (ii) a state where the spin is determined by Hund's rule, (iii) a state with the minimal possible spin. A transition from a state fulfilling Hund's rule, to a spin-polarized state occurs when decreasing the electron density. In the strong-coupling limit, the system of interacting polarons turns into a state with the minimal possible spin. These transitions should be experimentally observable in the optical absorption spectra of quantum dots.