Tuning biexciton binding and anti-binding in core/shell quantum dots

TL;DR

This paper employs quantum Monte Carlo simulations to accurately predict how quantum correlations influence biexciton binding in core/shell quantum dots, revealing transitions between binding and anti-binding states relevant for nanocrystal applications.

Contribution

It introduces a path integral quantum Monte Carlo method that captures all quantum correlations, providing new insights into biexciton binding behavior in various band alignment nanocrystals.

Findings

Biexcitons are binding with Type-I localization.

Biexcitons are strongly anti-binding with Type-II localization.

Perturbative methods miss the biexciton transition.

Abstract

We use a path integral quantum Monte Carlo method to simulate excitons and biexcitons in core shell nanocrystals with Type-I, II and quasi-Type II band alignments. Quantum Monte Carlo techniques allow for all quantum correlations to be included when determining the thermal ground state, thus producing accurate predictions of biexciton binding. These subtle quantum correlations are found to cause the biexciton to be binding with Type-I carrier localization and strongly anti-binding with Type-II carrier localization, in agreement with experiment for both core shell nanocrystals and dot in rod nanocrystal structures. Simple treatments based on perturbative approaches are shown to miss this important transition in the biexciton binding. Understanding these correlations offers prospects to engineer strong biexciton anti-binding which is crucial to the design of nanocrystals for single exciton lasing applications.