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Assessing the coupling between a plasmonic nanocavity and a single quantum emitter is challenging due to the lack of spatial control at the atomic scale. Here Zhanget al. achieve control with sub-nanometre precision and demonstrate the Fano resonance and Lamb shift at the single-molecule level.

Optical assembly of nanoparticle structures could open new avenues for manufacturing nanomaterials and devices. Herrmann et al.show the plasmon-induced laser threading of gold nanoparticle strings, enabling them to fabricate precisely assembled 12-nm wide conducting chains.

A theoretical framework that interprets Raman scattering as an optomechanical process can be used to understand, and guide, experiments in surface-enhanced Raman spectroscopy.

Stanford University researchers have demonstrated the potential of single SiC whiskers to function as narrowband infrared emitters that have controllable emission characteristics.

Low frequency vibrations of molecules are collective motions of many atoms, and thus very sensitive to their surroundings. Here, authors use light ultra-confined to the nanoscale, to measure single molecule vibrations below 1 THz. These show tapping and shearing motions, like waves on a string.

Scanning tunneling microscopy (STM) gives access to the atomic-scale properties of matter. Here, the authors showcase the fluorescent functionalization of an STM tip using a single molecule in direct metal contact, permitting the local electrostatic and -dynamic environment to be probed.

Optical anapoles in nanoresonators result in strong suppression of the electromagnetic radiation, which is challenging to detect in ideal settings. Here, the authors show that fast electrons are a powerful tool to circumvent this challenge due to their ability to access dark modes.

Vibrational strong coupling (VSC) promises ultrasensitive IR spectroscopy and modification of material properties. Here, nanoscale mapping of VSC between organic molecules and individual IR nanoresonators is achieved by remote near-field spectroscopy.

Extreme confinement of light in plasmonic nanocavities strongly enhances the optomechanical coupling of light with molecular vibrations. Here, the authors use a giant optical spring effect to reversibly weaken molecular bonds.

Strong coupling of quantum emitters to plasmonic cavities allows exploring rich phenomenologies of light-matter interaction. Here, the authors report experiments on single colloidal quantum dots coupled to plasmonic metal nanostructures, revealing complex interactions between bright and dark states.

Two gold nanostructures with controllable subnanometre separation are used to follow the evolution of plasmonic modes; the distance at which quantum tunnelling sets in is determined, and a quantum limit for plasmonic field confinement is estimated.

As lengthscales in plasmonic structures enter the sub-nanometre regime, quantum effects become increasingly important. Here, a quantum-corrected model is presented that addresses quantum effects in realistic-sized plasmonic structures, a situation not feasible for full-quantum-mechanical simulations.

Localized surface plasmon resonances induce strong modifications of surface-enhanced Raman spectra. Here the authors propose a robust method to retrieve the fingerprint of intrinsic chemical information by using the photoluminescence of the metallic structures to correct the spectra.

Strong coupling between light and matter can be engineered to influence their properties and behaviour. Here, the authors demonstrate the evolution from weak to ultrastrong coupling of microcavity modes and optical phonons with hexagonal boron nitride layers in a Fabry-Perot resonator.

Dynamic restructuring of metal nanoparticle surfaces greatly influences their catalytic, electronic transport, and chemical binding functionalities. Here, the authors show that non-equilibrium atomic-scale lattice defects can be detected in nanoparticles by using nano-optics at the sub-5nm scale.

Through the use of a plasmon-active atomically sharp tip and an ultrathin insulating film, and precise junction control in a highly confined nanocavity plasmon field at the scanning tunnelling microscope junction, sub-nanometre-resolved single-molecule near-field photoluminescence imaging with a spatial resolution down to ∼8 Å is achieved.

Single-cycle interferometric autocorrelation measurements of electrons tunnelling across the gap of a plasmonic bowtie antenna and quantitative models provide insight into the physical interactions that drive the electron transfer.

Here the authors adapt a STEM-EELS system to probe energy loss down to 100 meV, and apply it to map phononic states in hexagonal boron nitride, revealing that the electron loss is dominated by hyperbolic phonon polaritons.

We demonstrate on-demand CW sum-frequency generation from nanoparticle-on-mirror cavities positioned beneath a scanning probe tip. The tip controls visible and infrared fields within the nanocavity, allowing for tunable nonlinear spectroscopy.

Recent work has shown that quantum mechanical effects in plasmonic nanogap structures become important as the gap distances approach the subnanometre length-scale. Here, the authors review the major findings which challenge the classical picture of these structures and discuss future directions for the field.

Tautomerization, the interconversion between two constitutional isomers of a molecule, plays a major role in chemistry. The combination of hyper-resolved fluorescence microscopy with time-correlated measurements and spectral selection enables the identification and in-depth characterization of a tautomerization reaction within a single molecular switch.

Tip-enhanced Raman scattering (TERS) can be used to access the molecular composition and structure of surfaces with extreme lateral and depth resolution, down to the nanometre scale and beyond. In this Primer, Höppener et al. discuss the underlying physical principles driving the signal enhancement and lateral resolution of TERS.

Real-space mid-infrared nanoimaging reveals vibrational strong coupling between molecules and propagating phonon polaritons in unstructured, thin hexagonal boron nitride layers, which could provide a platform for testing strong coupling and local control of chemical properties.

This Review discusses the origins of localized plasmon resonances in few-nanometre or sub-nanometre gaps between metal nanoparticles and metal films, as well recent experimental observations and potential future directions.