Efficient nanophotonic devices are essential for applications in quantum networking, optical information processing, sensing, and nonlinear optics. Extensive research efforts have focused on integrating two-dimensional (2D) materials into photonic structures, but this integration is often limited by size and material quality. Here, we use hexagonal boron nitride (hBN), a benchmark choice for encapsulating atomically thin materials, as a waveguiding layer while simultaneously improving the optical quality of the embedded films. When combined with a photonic inverse design, it becomes a complete nanophotonic platform to interface with optically active 2D materials. Grating couplers and low-loss waveguides provide optical interfacing and routing, tunable cavities provide a large exciton-photon coupling to transition metal dichalcogenide (TMD) monolayers through Purcell enhancement, and metasurfaces enable the efficient detection of TMD dark excitons. This work paves the way for advanced 2D-material nanophotonic structures for classical and quantum nonlinear optics.

Rhombohedral trilayer graphene has recently emerged as a natural flat-band platform for studying interaction-driven symmetry-breaking phases. The displacement field (<i>D</i>) can further flatten the band to enhance the density of states, thereby controlling the electronic correlation that tips the energy balance between spin and valley degrees of freedom. To characterize the energy competition, chemical potential measurement─a direct thermodynamic probe of Fermi surfaces─is highly demanding to be conducted under a constant <i>D</i>. In this work, we characterize <i>D</i>-dependent isospin flavor polarization, where electronic states with isospin degeneracies of one and two can be identified. We also developed a method to measure the chemical potential at a fixed <i>D</i>, allowing for the extraction of energy variation during phase transitions. Furthermore, symmetry breaking could also be invoked in Landau levels, manifesting as quantum Hall ferromagnetism. Our work opens more opportunities for the thermodynamic characterization of displacement-field tuned van der Waals heterostructures.

We studied the supramolecular assembly of a multifunctional ligand, cis-bis-terpyridine tetraphenyl ethylene, on a Cu(111) surface by low-temperature scanning tunneling microscopy (STM). Three distinctive supramolecular structures, metallacycles, propeller-shaped clusters and extended linear chains, are formed under specific assembly conditions owing to different inter-molecular binding modes of Cu-coordination, van der Waals interaction and hydrogen bonding, respectively.

Transition metal dichalcogenide monolayers represent unique platforms for studying both electronic and phononic interactions as well as intra- and intervalley exciton complexes. Here, we investigate the upconversion of exciton photoluminescence in MoSe₂ monolayers. Within the nominal transparency window of MoSe₂ the exciton emission is enhanced for resonantly addressing the spin-singlet negative trion and neutral biexciton at a few tens of meV below the neutral exciton transition. We identify that the A'₁ optical phonon at the K valley provides the energy gain in the upconversion process at the trion resonance, while ZA(K) phonons with their spin- and valley-switching properties support the biexciton driven upconversion of the exciton emission. Interestingly, the latter upconversion process yields unpolarized exciton photoluminescence, while the former also leads to circularly polarized emission. Our study highlights high-order exciton complexes interacting with optical and acoustic K-valley phonons and upconverting light into the bright exciton.

The nanoscale periodic potential generated from moiré superlattices provides a new knob to tune and study the flat band effect and correlated physics. To date, moiré superlattices have been obtained using various two-dimensional (2D) materials, such as graphene, hexagonal boron nitride (hBN), transition metal dichalcogenides (TMDCs), and so on. In the 2D materials family, Janus monolayers of TMDCs have two different chalcogen atoms above and below the central metal atom. This asymmetric structure induced an out-of-plane electric field which provides an additional degree of freedom in moiré superlattices. Novel features in Janus materials were predicted by recent theoretical studies, such as: large Rashba spin–orbit coupling [1] , piezoelectricity [2] , and long-lived charge-transfer excitons [3] . Furthermore, recent calculations showed that excitons in Janus heterobilayer moiré superlattices are possible to realize high-temperature Bose–Einstein condensation state [3] .

Abstract Excitons in thin layers of semiconducting transition metal dichalcogenides are highly subject to the strongly modified Coulomb electron-hole interaction in these materials. Therefore, they do not follow the model system of a two-dimensional hydrogen atom. We investigate experimentally and theoretically excitonic properties in both the monolayer (ML) and the bilayer (BL) of MoSe 2 encapsulated in hexagonal BN. The measured magnetic field evolutions of the reflectance contrast spectra of the MoSe 2 ML and BL allow us to determine g -factors of intralayer A and B excitons, as well as the g -factors of the interlayer exciton. We explain the dependence of g -factors on the number of layers and excitation state can be explained using first principles calculations. Furthermore, we demonstrate that the experimentally measured ladder of excitonic s states in the ML can be reproduced using the k·p approach with the Rytova-Keldysh potential that describes the electron-hole interaction. In contrast, the analogous calculation for the BL case require taking into account the out-of-plane dielectric response of the MoSe 2 BL.

Data and codes for "Nonreciprocal Supercurrents in a Field-Free Graphene Josephson Triode"

We measure telegraph noise of current fluctuations in an electrostatically defined quantum dot in bilayer graphene by real-time detection of single electron tunneling with a capacitively coupled neighboring quantum dot. Suppression of the second and third cumulant (related to shot noise) in a tunable graphene quantum dot is demonstrated experimentally. With this method we demonstrate the ability to measure very low current and noise levels. Furthermore, we use this method to investigate the first spin excited state, an essential prerequisite to measure spin relaxation.