Manifestation of unconventional biexciton states in quantum dots

Abstract

Although semiconductor excitons consist of a fermionic subsystem (electron and hole), they carry an integer net spin similar to Cooper-electron-pairs. While the latter cause superconductivity by forming a Bose-Einstein-condensate, excitonic condensation is impeded by, for example, a fast radiative decay of the electron-hole pairs. Here, we investigate the behaviour of two electron-hole pairs in a quantum dot with wurtzite crystal structure evoking a charge carrier separation on the basis of large spontaneous and piezoelectric polarizations, thus reducing carrier overlap and consequently decay probabilities. As a direct consequence, we find a hybrid-biexciton complex with a water molecule-like charge distribution enabling anomalous spin configurations. In contrast to the conventional-biexciton complex with a net spin of s ¼ 0, the hybrid-biexciton exhibits s ¼ ± 3, leading to completely different photoluminescence signatures in addition to drastically enhanced charge carrier-binding energies. Consequently, the biexcitonic cascade via the dark exciton can be enhanced on the rise of temperature as approved by photon cross-correlation measurements.

Double-Well Ultracold-Fermions Computational Microscopy: Wave-Function Anatomy of Attractive-Pairing and Wigner-Molecule Entanglement and Natural Orbitals

“…More recently WMs have been found in other 2D QDs 26 , clean carbon nanotubes 27 , and for biexciton states in 3D QDs 28 .…”

Identifying multi-excitons in quantum dots: the subtle connection between electric dipole moments and emission linewidths

“…A mesa‐structured sample of wurtzite GaN/AlN QDs was investigated with a μ‐PL setup enabling single‐QD spectroscopy. A detailed description of the entire setup can be found elsewhere .…”

“…Here, the intensity scaling behaviour of particular complexes like the X and XX can e.g. be affected by non‐radiative processes or the overlay of different luminescence contributions causing n values that deviate from the ideal values of one and two. In order to determine this decisive value for the particular case of X and XX emission one has to simultaneously fit the data from Fig.…”

“…(right). The determination of rather ideal scaling values of around 1 and 2 for the X and XX clearly supports the given emission line identification, even though the absolute values can be affected by non‐radiative decay processes . Nevertheless, only the full set of identification methods for single QD emission lines can solidify the emission line assignment.…”

Accessing the dark exciton spin in deterministic quantum-dot microlenses

“…21 The optical access to the DE is enabled via excited biexcitonic states containing two charge carriers with parallel spins. 22,23 In this work, we employ deterministically fabricated microlenses above pre-selected QDs grown by metal-organic chemical vapor deposition (MOCVD) to optically prepare and read out the DE spin qubit and observe its coherent precession. The use of a geometric microlens approach, rather than a narrow-band microcavity, is highly beneficial in our experiment, as the lens provides efficient photon extraction over a wide spectral range.…”