Evolution of excitons via biexcitons to an electron-hole plasma without level crossing between band edge and exciton in a quantum wire

TL;DR

This study observes the evolution of excitons to an electron-hole plasma in a quantum wire without the expected level crossing, challenging existing theories about exciton and plasma interactions.

Contribution

It provides experimental evidence that the plasma PL line edge never crosses the exciton peak, contradicting prevailing theoretical models.

Findings

Biexcitons observed at specific pair densities

PL line broadens into plasma without energy shift

No crossing of plasma line edge with exciton peak

Abstract

A recent single quantum wire is of sufficient quality to reveal new details of the photoluminescence (PL) evolution with increasing electron--hole (e--h) pair density. At a pair density of 3.6 $\times$ 10$^{3}$ cm$^{-1}$, the PL is characteristic of biexcitons shifted below the exciton peak by the 2.8-meV biexciton binding. At the pair density of 1.2 $\times$ 10$^{5}$ cm$^{-1}$, the biexciton peak broadens without energy shift to an e--h plasma. At all pair densities up to 30 K, neither the exciton peak nor the one-dimensional (1D) continuum edge shows any shift. In contrast to prevailing theories, the low-energy edge of the plasma PL line never crosses the exciton peak and never makes contact with the 1D e--h continuum.