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A new platform making use of hexagonal boron nitride interfaced with the molecular superconductor κ-(BEDT-TTF)₂Cu[N(CN)₂]Br is demonstrated for realizing cavity-altered materials, confirmed by magnetic force microscopy and nano-optical measurements.

Here, the authors use scanning probe photocurrent imaging to resolve nanoscale variations of the Seebeck coefficient occurring at domain walls separating micron-scale AB and BA stacking regions in twisted bilayer graphene, and observe hyperbolic enhancement of the photocurrent pattern.

Traditional photonic crystals consist of periodic media with a pre-defined optical response. Here, the authors combine nanostructured back-gate insulators with a continuous layer of graphene to demonstrate an electrically tunable two-dimensional photonic crystal suitable for controlling the propagation of surface plasmon polaritons.

The authors use time-resolved scanning near-field optical microscopy to probe the ultrafast excitonic processes and their impact on waveguide operation in transition metal dichalcogenide crystals. They observe significant modulation of the complex index by monitoring waveguide modes on the fs time scale, and identify both coherent and incoherent manipulations of WSe₂ excitonic resonances.

Solitons may develop when strain forms at line defects separating commensurate domains in misaligned or lattice-mismatched van der Waals heterostructures. Here, the authors use atomic-force microscopy and nano-infrared spectroscopy to image solitons in thin hBN crystals in the form of long-range periodic superstructures, creating sub-surface hexagonal networks with periods of a few hundred nanometers.

Graphene/hBN moiré superlattices exhibit a new set of Dirac mini-bands, whose interband transitions—together with free electrons in the ordinary Dirac bands—modify the nature of the plasmons, as revealed by infrared near-field microscopy.

Exploiting non-local optical resonances on 3R-MoS₂ flakes, researchers demonstrate single-pass second-harmonic conversion efficiencies of ~10⁻⁴ over only 160-nm-thick van der Waals nonlinear metastructures at telecom wavelengths.

A nano-optical probe of the Purcell effect in a van der Waals waveguide is demonstrated, exploiting its highly confined infrared waveguide modes and the capacity for infrared emission in the monolayer limit of atomically layered van der Waals materials.

The high-contrast dielectric boundary between a gold–air hybrid structure and its sharp spatial features are exploited to provide the momentum required for the excitation of higher-order hyperbolic phonon polaritons.

The emergence of magnetically confined surface excitons enabled by antiferromagnetic spin correlations is reported, which leads to the confinement of excitons to the surface of layered antiferromagnet CrSBr.

Here, the authors report the observation of two solid-state analogues of well-known high-energy physics effects in graphene samples irradiated by infrared photons under non-equilibrium conditions. Depending on the carrier density of graphene, they observed asymmetric plasmon damping, and anomalous photocurrents associated with the condensed matter versions of the Cherenkov and Schwinger effects.

An optical method images nonlinear optical processes in waveguides with femtosecond and nanometre precision. The approach is used to achieve phase-matched second-harmonic generation in 3R-MoS₂ waveguides.

The authors demonstrate a graphene/CrSBr heterostructure exhibiting anisotropic surface plasmon polariton (SPP) propagation in the mid-infrared and terahertz range. Charge transfer at the interface directs SPPs along the quasi-1D chains that compose each CrSBr layer, with propagation lengths varying by an order of magnitude between the two in-plane crystallographic axes.

Dirac magnetoexcitons with non-trivial nanoscale electrodynamics are formed from the excitation of Landau levels in charge-neutral graphene. Here, the Dirac magnetoexciton dispersion is directly imaged up to 7 T via a magneto cryogenic near-field microscope.

The ability to control both electric and magnetic dispersion of light allows a novel type of hyperbolic material with impedance matched to air. Here, the authors show experimentally a topological transition between elliptic and magnetic hyperbolic dispersions in a metamaterial for control of thermal radiation.

s-SNOM is a powerful tool, but it is less sensitive to in-plane variations. Here the authors present a method to improve this with a metallic microdisk antenna, which they demonstrate by probing in-plane phonon responses.

Researchers created a periodically poled van der Waals semiconductor (3R-MoS₂) and achieved a macroscopic frequency conversion efficiency of 0.03% over a thickness of 3.4 μm. The quasi-phase-matched second harmonic signal surpasses the usual quadratic enhancement by 50% and broadband generation of photon pairs at telecom wavelength is demonstrated with a coincidence-to-accidental ratio of 638 ± 75.

Excitons play an important role in the optical properties of 2D semiconductors, but their spatial characterization is usually constrained by the diffraction limit. Here, the authors report near-field optical spectroscopy of 2D transition metal dichalcogenides with 20 nm resolution, revealing their spatially dependent excitonic spectra and complex dielectric function.

Hyperbolic exciton polaritons (HEPs) are anisotropic light-matter excitations with promising applications, but their steady-state observation is challenging. Here, the authors report experimental evidence of HEPs in a van der Waals magnet, CrSBr, via cryogenic infrared near-field microscopy.

Direct infrared nano-imaging of plasmonic waves in graphene carrying high current density reveals the Fizeau drag of plasmon polaritons by fast-moving quasi-relativistic electrons.

In moiré materials, structural relaxation phenomena can lead to unexpected and novel material properties. Here, the authors characterize an unconventional non-local relaxation process in twisted double trilayer graphene, in which an energy gain in one domain of the moiré lattice is paid for by a relaxation that occurs in the other.

Recent experiments have shown the formation of ferroelectric domains in twisted van der Waals bilayers. Here, the authors report near-field infrared nano-imaging and nano-photocurrent measurements to investigate ferroelectricity in minimally twisted WSe₂ by visualizing the plasmonic and photo-thermoelectric response of an adjacent graphene monolayer.

We present comprehensive thermodynamic and spectroscopic evidence for an antiferromagnetically ordered heavy-fermion ground state in the van der Waals metal CeSiI.

Mode-selective vibrational excitations can be used to transiently induce a range of phenomena in strongly correlated states of matter. It is now shown that by exciting apical oxygen distortions in the cuprate system YBa₂Cu₃O_6.5, an unusual photoconductive effect is induced both at low and at high temperatures.

Researchers demonstrate efficient frequency conversion with rhombohedral MoS₂. A second-harmonic-generation coherence length of ~530 nm at 1,520 nm wavelength and giant nonlinear optical enhancement in waveguide geometries are reported.

Strong electrorefractive effects in semiconductor transition metal dichalcogenides (TMDs) at near-infrared wavelengths, where the TMDs are transparent, are observed and used to demonstrate photonic devices based on a composite SiN–TMD platform with large phase modulation, minimal induced loss and low electrical power consumption.

Plasmons are directly launched in graphene, and their key parameters — propagation and attenuation — are studied with near-field infrared nano-imaging.

Here, a combined experiment-theory framework based on different nano-imaging techniques and first-principle calculations is used to analyse the shapes of moiré patterns in twisted van der Waals structures, enabling an accurate description of the coupling between the atomically thin layers.

The photonic applications of hyperbolic phonon polaritons (HPhPs) in anisotropic van der Waals materials are currently limited by their low tunability. Here, the authors report the static and ultrafast wavevector modulation of HPhPs in hexagonal boron nitride by tuning the plasma frequency of doped semiconductor substrates.

Hexagonal boron nitride has many interesting properties, including a natural hyperbolic dispersion, making it attractive for nanophotonic applications. Here, Dai et al. show that metallic disks under the material launch phonon–polaritons, turning it into a hyper-focusing lens.

Individual grain boundaries are imaged using a scanning plasmon interferometry technique, revealing mechanistic insights on electronic transport and plasmon propagation in graphene.

A two-dimensional crystalline polymer of C₆₀, termed graphullerene, is synthesized by chemical vapour transport, and mechanically exfoliated to produce molecularly thin flakes with clean interfaces for potential optoelectronic applications.

Strain engineering can ‘hide’ the ordinal ferrometallic state in manganite films, pushing the system to a metastable state, which can then be controlled through photoexcitation.

Non-equilibrium photoinduced plasmons in a high-mobility graphene monolayer are investigated at infrared wavelengths.

The combination of piezoresponse force microscopy and optical measurements reveals the influence of strain in the formation of one-dimensional moiré patterns and the resulting behaviour of interlayer excitons in van der Waals heterostructures.

Infrared spectra of graphene deposited on a silicon oxide substrate suggest that many-body effects have a more significant role in determining its electronic behaviour than in free-standing graphene

A near-field optical microscopy study provides nanoscale insight into an insulator-to-metal transition and the interplay with a neighbouring structural phase transition in a prototypical correlated electron material.

The amplitude and wavelength of hyperbolic phonon polaritons in hexagonal boron nitride can be tuned using a monolayer graphene gate.

Hyperbolic phonon polaritons – mixed states of photons and anisotropic lattice vibrations – offer appealing properties for nanophotonic applications. Here, the authors show that the plasmon-phonon hybridization upon electronic doping in graphene/α-MoO3 heterostructures can induce topological transitions of the polariton wavefront.