A tunable nanotip optical cavity controls hybrid quantum states of a single emitter at room temperature.

Photoluminescence (PL), a photo‐excited spontaneous emission process, provides a wealth of optical and electronic properties of materials, which enable microscopic and spectroscopic imaging, biomedical sensing and diagnosis, and a range of photonic device applications. However, conventional far‐field PL measurements have limitations in sensitivity and spatial resolution, especially to investigate single nano‐materials or nano‐scale dimension of them. In contrast, tip‐enhanced photoluminescence (TEPL) nano‐spectroscopy provides an extremely high sensitivity with <10 nm spatial resolution, which allows the desired nano‐scale characterizations. With outstanding and unique optical properties, low‐dimensional quantum materials have recently attracted much attention, and TEPL characterizations, i. e., probing and imaging, and even control at the nano‐scale, have been extensively studied. In this review, we discuss the fundamental working mechanism of PL enhancement by plasmonic tip, and then highlight recent advances in TEPL studies for low‐dimensional quantum materials. Finally, we discuss several remaining challenges of TEPL nano‐spectroscopy and nano‐imaging, such as implementation in non‐ambient media and in situ environments, limitations in sample structure, and control of near‐field polarization, with perspectives of the approach and its applications.

Understanding and controlling the nanoscale transport of excitonic quasiparticles in atomically thin two-dimensional (2D) semiconductors are crucial to produce highly efficient nano-excitonic devices. Here, we present a nanogap device to selectively confine excitons or trions of 2D transition metal dichalcogenides at the nanoscale, facilitated by the drift-dominant exciton funneling into the strain-induced local spot. We investigate the spatiospectral characteristics of the funneled excitons in a WSe ₂ monolayer (ML) and converted trions in a MoS ₂ ML using hyperspectral tip-enhanced photoluminescence imaging with <15-nm spatial resolution. In addition, we dynamically control the exciton funneling and trion conversion rate by the gigapascal-scale tip pressure engineering. Through a drift-diffusion model, we confirm an exciton funneling efficiency of ∼25% with a significantly low strain threshold (∼0.1%), which sufficiently exceeds the efficiency of ∼3% in previous studies. This work provides a previously unexplored strategy to facilitate efficient exciton transport and trion conversion of 2D semiconductor devices.