Moiré superlattices provide a powerful tool to engineer novel quantum phenomena in twodimensional (2D) heterostructures, where the interactions between the atomically thin layers qualitatively change the electronic band structure of the superlattice. For example, mini-Dirac points, tunable Mott insulator states, and the Hofstadter butterfly can emerge in different types of graphene/boron nitride moiré superlattices, while correlated insulating states and superconductivity have been reported in twisted bilayer graphene moiré superlattices 1-12 . In addition to their dramatic effects on the single particle states, moiré superlattices were recently predicted to host novel excited states, such as moiré exciton bands [13][14][15] . Here we report the first observation of moiré superlattice exciton states in nearly aligned WSe 2 /WS 2 heterostructures.These moiré exciton states manifest as multiple emergent peaks around the original WSe 2 A exciton resonance in the absorption spectra, and they exhibit gate dependences that are distinctly different from that of the A exciton in WSe 2 monolayers and in large-twist-angle WSe 2 /WS 2 heterostructures. The observed phenomena can be described by a theoretical model where the periodic moiré potential is much stronger than the exciton kinetic energy and creates multiple flat exciton minibands. The moiré exciton bands provide an attractive platform to explore and control novel excited state of matter, such as topological excitons and a correlated exciton Hubbard model, in transition metal dichalcogenides.

Moiré superlattices are emerging as a new route for engineering strongly correlated electronic states in two-dimensional van der Waals heterostructures, as recently demonstrated in the correlated insulating and superconducting states in magic-angle twisted bilayer graphene and ABC trilayer graphene/boron nitride moiré superlattices 1-4 . Transition metal dichalcogenide (TMDC) moiré heterostructures provide another exciting model system to explore correlated quantum phenomena 5 , with the addition of strong light-matter interactions and large spin-orbital coupling. Here we report the optical detection of strongly correlated phases in semiconducting WSe2/WS2 moiré superlattices. Our sensitive optical detection technique reveals a Mott insulator state at one hole per superlattice site (ν = 1), and surprising insulating phases at fractional filling factors ν = 1/3 and 2/3, which we assign to generalized Wigner crystallization on an underlying lattice 6-9 . Furthermore, the unique spin-valley optical selection rules 10-12 of TMDC heterostructures allow us to optically create and investigate low-energy spin excited states in the Mott insulator. We reveal an especially slow spin relaxation lifetime of many microseconds in the Mott insulating state, orders-of-magnitude longer than that of charge excitations. Our studies highlight novel correlated physics that can emerge in moiré superlattices beyond graphene.

While research on the disclosure of CSR (corporate social responsibility) recognizes the influence of government regulations and guidelines, less attention has been given to the co-existence of conflicting pressures from the state. We develop a framework wherein CSR reporting is viewed as an organizational response to institutional complexity that arises from the conflicting demands from the central government and local governments, and apply it to publicly listed firms in China after the central government agencies issued guidelines on CSR reporting. Some provincial governments' high priority given to short-term GDP growth created tension with the central government's expectations on CSR reporting. Firms with attributes that increase scrutiny from both institutional constituencies experienced heightened tension, and they responded with early adoption but low-quality reports. Our framework was supported through a longitudinal analysis between 2008 and 2011. Our study contributes to the literature on CSR disclosure by uncovering the impact of conflicting government pressures, and advances research on institutional complexity by identifying a specific decoupling response.

Single band-edge states can trap light and function as high-quality optical feedback for microscale lasers and nanolasers. However, access to more than a single band-edge mode for nanolasing has not been possible because of limited cavity designs. Here, we describe how plasmonic superlattices-finite-arrays of nanoparticles (patches) grouped into microscale arrays-can support multiple band-edge modes capable of multi-modal nanolasing at programmed emission wavelengths and with large mode spacings. Different lasing modes show distinct input-output light behaviour and decay dynamics that can be tailored by nanoparticle size. By modelling the superlattice nanolasers with a four-level gain system and a time-domain approach, we reveal that the accumulation of population inversion at plasmonic hot spots can be spatially modulated by the diffractive coupling order of the patches. Moreover, we show that symmetry-broken superlattices can sustain switchable nanolasing between a single mode and multiple modes.

Plasmonics is a rapidly developing field at the boundary of physical optics and condensed matter physics. It studies phenomena induced by and associated with surface plasmons-elementary polar excitations bound to surfaces and interfaces of nanostructured good metals. This Roadmap is written collectively by prominent researchers in the field of plasmonics. It encompasses selected aspects of nanoplasmonics. Among them are fundamental aspects such as quantum plasmonics based on quantum-mechanical properties of both underlying materials and plasmons themselves (such as their quantum generator, spaser), plasmonics in novel materials, ultrafast (attosecond) nanoplasmonics, etc. Selected applications of nanoplasmonics are also reflected in this Roadmap, in particular, plasmonic waveguiding, practical applications of plasmonics enabled by novel materials, thermo-plasmonics, plasmonic-induced photochemistry and photo-catalysis. This Roadmap is a concise but authoritative overview of modern plasmonics. It will be of interest to a wide audience of both fundamental physicists and chemists and applied scientists and engineers.

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This review focuses on structural engineering of lasers from the macroscale to the nanoscale, with an emphasis on plasmon nanolasers. Conventional lasers based on Fabry-Pérot cavities are limited in device size. In contrast, plasmon nanolasers can overcome the diffraction limit of light and incorporate unique structural designs to engineer cavity geometries and optical band structure. Since the spaser concept was introduced in 2003, tremendous progress in nanolasing has been made on architectures that exploit metal films and nanoparticles. Theoretical approaches in both frequency and time domains have inspired the development of plasmon nanolasers based on mode analysis and time-dependent lasing buildup. Plasmon nanolasers designed by band-structure engineering open prospects for manipulation of lasing characteristics such as directional emission, real-time tunable wavelengths, and controlled multimode lasing.

This paper reports a robust and stretchable nanolaser platform that can preserve its high mode quality by exploiting hybrid quadrupole plasmons as an optical feedback mechanism. Increasing the size of metal nanoparticles in an array can introduce ultrasharp lattice plasmon resonances with out-of-plane charge oscillations that are tolerant to lateral strain. By patterning these nanoparticles onto an elastomeric slab surrounded by liquid gain, we realized reversible, tunable nanolasing with high strain sensitivity and no hysteresis. Our semiquantum modeling demonstrates that lasing build-up occurs at the hybrid quadrupole electromagnetic hot spots, which provides a route toward mechanical modulation of light-matter interactions on the nanoscale.