# Circularly Polarized Luminescence Without External Magnetic Fields from Individual CsPbBr3 Perovskite Quantum Dots

## TL;DR

Researchers found that individual CsPbBr3 quantum dots can emit circularly polarized light without needing a magnetic field, offering new insights into their optical properties.

## Contribution

The study reveals that individual CsPbBr3 quantum dots can exhibit circular polarization in exciton states without external magnetic fields.

## Key findings

- Individual CsPbBr3 quantum dots show up to 38% circular polarization in their exciton fine-structure states.
- A transition from left- to right-hand circular polarization was observed within the fine-structure triplet manifold.
- Conventional polarimetric techniques failed to detect the circular polarization observed in this study.

## Abstract

Lead halide perovskite
quantum dots (QDs), the latest generation
of the colloidal QD family, exhibit outstanding optical properties,
which are now exploited as both classical and quantum light sources.
Most of their rather exceptional properties are related to the peculiar
exciton fine-structure of band-edge states, which can support unique
bright triplet excitons. The degeneracy of the bright triplet excitons
is lifted with energetic splitting in the order of millielectronvolts,
which can be resolved by the photoluminescence (PL) measurements of
single QDs at cryogenic temperatures. Each bright exciton fine-structure-state
(FSS) exhibits a dominantly linear polarization, in line with several
theoretical models based on the sole crystal field, exchange interaction,
and shape anisotropy. Here, we show that in addition to a high degree
of linear polarization, the individual exciton FSS can exhibit a non-negligible
degree of circular polarization even without external magnetic fields
by investigating the four Stokes parameters of the exciton fine-structure
in individual CsPbBr3 QDs through Stokes polarimetric measurements.
We observe a degree of circular polarization up to ∼38%, which
could not be detected by using the conventional polarimetric technique.
In addition, we found a consistent transition from left- to right-hand
circular polarization within the fine-structure triplet manifold,
which was observed in magnetic-field-dependent experiments. Our optical
investigation provides deeper insights into the nature of the exciton
fine structures and thereby drives the yet-incomplete understanding
of the unique photophysical properties of this class of QDs for the
benefit of future applications in chiral quantum optics.