Nanoscale confinement and control of excitonic complexes in a monolayer WSe2

TL;DR

This paper introduces a cryogenic capacitive confocal optical microscope (C3OM) that enables nanoscale control and observation of excitonic complexes in monolayer WSe2, advancing understanding and manipulation of quasiparticles in 2D semiconductors.

Contribution

The study presents a novel nanoscale optical microscopy technique using a conductive AFM tip as a gate to modulate excitonic states at cryogenic temperatures.

Findings

Nanoscale confinement of exciton and trion peaks achieved.

Observation of a distinct photoluminescence line with nonlinear response.

Demonstration of nanoscale spectroscopy of excitonic complexes.

Abstract

Nanoscale control and observation of photophysical processes in semiconductors is critical for basic understanding and applications from optoelectronics to quantum information processing. In particular, there are open questions and opportunities in controlling excitonic complexes in two-dimensional materials such as excitons, trions or biexcitons. However, neither conventional diffraction-limited optical spectroscopy nor lithography-limited electric control provides a proper tool to investigate these quasiparticles at the nanometer-scale at cryogenic temperature. Here, we introduce a cryogenic capacitive confocal optical microscope (C3OM) as a tool to study quasiparticle dynamics at the nanometer scale. Using a conductive atomic force microscope (AFM) tip as a gate electrode, we can modulate the electronic doping at the nanometer scale in WSe2 at 4K. This tool allows us to modulate with nanometer-scale confinement the exciton and trion peaks, as well a distinct photoluminescence line associated with a larger excitonic complex that exhibits distinctive nonlinear optical response. Our results demonstrate nanoscale confinement and spectroscopy of exciton complexes at arbitrary positions, which should prove an important tool for quantitative understanding of complex optoelectronic properties in semiconductors as well as for applications ranging from quantum spin liquids to superresolution measurements to control of quantum emitters.