The layered antiferromagnet CrSBr features magnons coupled to other quasiparticles, including excitons and polaritons, enabling their easy optical accessibility. In this work, we investigate the tunability of magnons in few-layered devices in response to changes in carrier density and the application of a perpendicular electric field. We demonstrate an on-chip tunability of the in- and out-of-phase magnon frequencies by up to 2 GHz. While the frequencies of both modes increase with the electron density, we observe an asymmetric response with respect to the electric field in a dual-gated trilayer device. To understand the mechanism of this disparity, we develop a layer-resolved macrospin model describing the magnetic dynamics in thin, non-uniformly doped devices. Through this model we establish the doping- and electric-field-dependence of the exchange interaction, magnetic anisotropy, and magnetic moment of individual layers. Our results advance the applications of gate-tunable magnonic devices based on 2D materials.

The structure and electrostatics of liquids change dramatically under nanometric confinement, suggesting that solvent-solute interactions in such environments differ fundamentally from those in the bulk. Here, we combine nanoscale Fourier-transform infrared spectroscopy (nanoFTIR) with the vibrational Stark effect (VSE) to directly map the local electric field experienced by a molecular probe—the C=O stretching vibration of dimethylformamide (DMF)—within buried nanofluidic channels. To this end, we fabricated hexagonal boron nitride (hBN)-capped trenches with depths ranging from ~100 nm down to 2.6 nm and filled them with a 1:1 (v/v) aqueous DMF solution. Under the strongest confinement (2.6 nm), the DMF C=O stretching mode exhibits a +17 cm -1 blueshift, corresponding to a substantial change in the local solvation electric field strength of 0.39 V Å -1 . Molecular dynamics (MD) simulations, combined with MD-derived IR spectra, reproduce the observed spectral shift and the associated change in local solvation electrostatics. The simulations further reveal the emergence of a quasi-phase-separated interfacial layer under finite-size confinement as the origin for the altered electrostatics. Together, these results establish nanoFTIR-based VSE spectroscopy as a direct and quantitative probe of nanosolvation electrostatics in nanoscale fluidic reactors.

Discrete time crystals (DTCs) are emergent non-equilibrium phases of periodically driven many-body systems, with potential applications ranging from quantum computing to sensing and metrology. There has been significant recent interest in understanding mechanisms leading to DTC formation and a search for novel DTC phases beyond subharmonic entrainment. Here, we report observation of multiple DTC phases in a nanoelectromechanical system (NEMS) based on coupled graphene and silicon nitride membranes. We confirm the time-crystalline nature of these symmetry broken phases by establishing their many-body characters, long-range time and spatial order, and rigidity against parameter fluctuation or noise. Furthermore, we employ controlled mechanical strain to drive the transitions between phases with different symmetries, thereby mapping the emergent time-crystalline phase diagram. Overall, our work takes a step towards establishing time crystals as a system with complexity rivaling that of solid state crystals.

Two-dimensional materials provide a rich platform to explore phenomena such as emerging electronic and excitonic states, strong light-matter coupling and new optoelectronic device concepts. The optical response of monolayers is entangled with the substrate on which they are grown or deposited on, often a two-dimensional material itself. Understanding how the properties of the two-dimensional monolayers can be tuned via the substrate is therefore essential. Here we employ angle-resolved reflectivity and photoluminescence spectroscopy on highly ordered molecular monolayers on hexagonal boron nitride (hBN) to systematically investigate the angle-dependent optical response as a function of the thickness of the hBN flake. We observe that light reflection and emission occur in a strongly directed fashion and that the direction of light reflection and emission is dictated by the hBN flake thickness. Transfer matrix simulations reproduce the experimental data and show that optical interference effects in hBN are at the origin of the angle-dependent optical properties. While our study focuses on molecular monolayers on hBN, our findings are general and relevant for any 2D material placed on top of a substrate. Our findings demonstrate the need to carefully choose substrate parameters for a given experimental geometry but also highlight opportunities in applications such as lighting technology where the direction of light emission can be controlled via substrate thickness.

Encoding and manipulating digital information in quantum degrees of freedom is one of the major challenges of today's science and technology. The valley indices of excitons in transition metal dichalcogenides (TMDs) are well-suited to address this challenge. Here, we demonstrate a new class of strain-tunable, valley-polarized hybrid excitons in monolayer TMDs, comprising a pair of energy-resonant intra- and intervalley excitons. These states combine the advantages of bright intravalley excitons, where the valley index directly couples to light polarization, and dark intervalley excitons, characterized by low depolarization rates. We demonstrate that the hybridized state of dark KK' intervalley and defect-localized excitons exhibits a degree of circular polarization of emitted photons that is three times higher than that of the constituent species. Moreover, a bright KK intravalley and a dark KQ exciton form a coherently coupled hybrid state under energetic resonance, with their valley depolarization dynamics slowed down a hundredfold. Overall, these valley-polarized hybrid excitons with strain-tunable valley character emerge as prime candidates for valleytronic applications in future quantum and information technology.

We investigate spin relaxation dynamics of interlayer excitons in a MoSe2/MoS2 heterostructure induced by the Rashba effect. In such a system, Rashba interactions arise from an out-of-plane electric field due to photo-generated interlayer excitons inducing a phonon-assisted intravalley spin relaxation. We develop a theoretical description based on a microscopic approach to quantify the magnitude of Rashba interactions and test these predictions via time-resolved Kerr rotation measurements. In agreement with the calculations, we find that the Rashba-induced intravalley spin mixing becomes the dominating spin relaxation channel above T = 50 K. Our work identifies a previously unexplored spin-depolarization channel in heterostructures which can be used for ultrafast spin manipulation.

Encoding and manipulating digital information in quantum degrees of freedom is one of the major challenges of today's science and technology. The valley indices of excitons in transition metal dichalcogenides (TMDs) are well-suited to addressing this challenge. Here, we employ mechanical strain to manipulate intervalley interactions and tune the valley polarization dynamics of excitons across a broader range of momentum space in monolayer TMDs. We use strain engineering to form valley-hybridized excitons that combine the advantages of bright intravalley excitons, where the valley index directly couples to light polarization, and dark intervalley excitons, characterized by low depolarization rates. We demonstrate that these valley-hybridized excitons exhibit signatures of coherently coupled states with a 100-fold reduction in valley depolarization rate and up to a 5-fold increase in steady-state valley polarization compared to previously studied excitons. Our findings of strain-tunable valley character of excitons advance the applications of TMDs in valleytronics.

Hexagonal boron nitride is distinguished among solid-state materials with luminescent properties as a material to create single-photon sources efficiently emitting at room temperature. In this work, it is demonstrated that helium ion irradiation with fluences of (1–5) × 1014 ion/cm2 increases the ultraviolet radiation intensity with a maximum at a wavelength of 320 nm due to the formation of new luminescent centers. The subsequent electron irradiation further increases the intensity of 320 nm luminescence apparently due to the formation of carbon-containing defects in the volume of hBN through recombination-enhanced migration. On the contrary, the intense helium ion irradiation stimulates the formation of nonradiative recombination centers, which reduce the lifetime of nonequilibrium charge carriers.

Single-photon emission centers generated by controlled atomic force microscope (AFM) indentation in monolayer WSe2 on a flexible polymer substrate are explored for applications in quantum technologies. Here, we study the response of these emitters to the polymer substrate's strain state, which is controlled by selecting the indentation force and by gradually thermally annealing the samples. In the indented areas, we observe sharp new photoluminescence peaks in the regions 1.62-1.68 eV and 1.70-1.73 eV characterized by sublinear power dependence and spectral wandering. We find that these peaks arise only when the indentation force exceeds a few mu N and generally red-shift as the applied force increases. Conversely, after thermal annealing (T <60 degrees C), WSe2 experiences strain relaxation, leading to a blue shift of the peaks' spectral position and their ultimate disappearance. Our analysis of the peaks' positions vs strain allows us to draw several conclusions about the nature of these emission. Specifically, we elucidate the roles of excitonic confinement and hybridization between free excitons and defect-related states, a process activated by the strain level. Overall, our approach suggests that the energy of localized emitters may be controlled via strain engineering.

Single-photon emitters (SPEs) are crucial in quantum communication and information processing. In 2D transition metal dichalcogenides (TMDs), SPEs are realized through inhomogeneous strain, while in combination with 2D magnets, a high spontaneous out-of-plane magnetization can be induced due to proximity effects. Here, an alternative is proposed that consists of suspending a TMD monolayer (WSe2) on a few-layer antiferromagnet (CrSBr) with in-plane magnetic ordering. The resulting heterostructure exhibits localization centers at lower energies than expected. Among them, a bright SPE with a high degree of polarization selection is identified. This suffers a clear energy shift driven by an in-plane magnetic field, and interestingly, this shift is correlated with the metamagnetic transition of CrSBr, suggesting a new kind of proximity-type effect. Unlike regular SPEs in WSe2 (sensitive to out-of-plane magnetic fields), our SPE demonstrates sensitivity to both in-plane and out-of-plane magnetic fields. The added tunability at significantly lower fields offers a promising direction for developing magnetically responsive quantum emitters, paving the way for more practical applications in quantum technologies.

Confocal microscopy is an invaluable tool for studying fluorescent materials and finds a wide application in biology and in quantum sensing. Usually, these experiments are performed under ambient conditions, but many materials are air sensitive (for example, black phosphorus) and degrade quickly under the strong laser irradiance. Here, we present a glovebox-integrated confocal microscope designed for nitrogen-vacancy (NV) center-based nano-scale sensing and NMR spectroscopy in an inert gas atmosphere. Using black phosphorus as a test material, we confirm that the glovebox maintains low oxygen levels and prevents material degradation during laser exposure. We demonstrate the setup's capabilities through experiments that show NV center detection and spin manipulation under a black phosphorus flake. This custom-built system enables the study of air-sensitive materials and opens new perspectives for exploring surface chemistry in a controlled environment. Our work outlines both the strengths and the challenges of using a glovebox-integrated confocal microscope for quantum technology applications.

Momentum-indirect excitons composed of electrons and holes in different valleys define optoelectronic properties of many semiconductors, but are challenging to detect due to their weak coupling to light. The identification of an excitons' valley character is further limited by complexities associated with momentum-selective probes. Here, we study the photoluminescence of indirect excitons in controllably strained prototypical 2D semiconductors (WSe$_2$, WS$_2$) at cryogenic temperatures. We find that these excitons i) exhibit valley-specific energy shifts, enabling their valley fingerprinting, and ii) hybridize with bright excitons, becoming directly accessible to optical spectroscopy methods. This approach allows us to identify multiple previously inaccessible excitons with wavefunctions residing in K, $\Gamma$, or Q valleys in the momentum space as well as various types of defect-related excitons. Overall, our approach is well-suited to unravel and tune intervalley excitons in various semiconductors.

The change in the intensity of cathodoluminescence of hexagonal boron nitride in the short-wavelength spectral region upon electron beam excitation is investigated. It is shown that the intensity of the peak at a wavelength of 215 nm, associated with the band-to-band transitions, decreases during electron excitation and tends to a stationary value, whereas the intensity of the peak at 320 nm increases under electron irradiation. This band is likely caused by the formation of luminescence centers under electron irradiation.

Single photons emitters (SPEs) are key components in quantum information applications and are commonly generated in 2D materials by inhomogeneous strain engineering. Here, we report an alternative approach that involves a 2D semiconductor/2D magnet heterostructure. The optical study of the WSe2/CrSBr heterostructures reveals several new emission lines at lower energies compared to characteristic WSe2 emissions, that are assigned to localized excitons. Further investigation demonstrates that one of these emergent lines is an SPE with a strong valley polarization response and large energy shift with the field-induced metamagnetic transition in CrSBr, linking it to the magnetic proximity effect of the adjacent CrSBr layer. In contrast to previous reports on WSe2 that only allow tuning of the SPEs by out-of-plane magnetic field, our emitter is sensitive to both in- and out-of-plane fields. Our findings demonstrate the potential of this approach for improved control and polarization of SPEs in 2D materials.

Excitons in Transition Metal Dichalcogenides (TMDs) acquire a spin-like quantum number, a pseudospin, originating from the crystal's discrete rotational symmetry. Here, we break this symmetry using a tunable uniaxial strain, effectively generating a pseudomagnetic field exceeding 40 Tesla. Under this large field, we demonstrate pseudospin analogs of spintronic phenomena such as the Zeeman effect and Larmor precession. Moreover, we determine previously inaccessible fundamental properties of TMDs, including the strength of the depolarizing field responsible for the loss of exciton coherence. Finally, we uncover the bosonic – as opposed to fermionic – nature of many-body excitonic species using the pseudomagnetic equivalent of the g-factor spectroscopy. Our work is the first step toward establishing this spectroscopy as a universal method for probing correlated many-body states and realizing pseudospin analogs of spintronic devices.

Functionalization of pristine graphene by hydrogen and fluorine is well studied, resulting in graphane and fluorographene structures. In contrast, functionalization of pristine graphene with iodine has not been reported. Here, the functionalization of graphene with iodine using photochemical activation is presented, which is thermally reversible at 400 degrees C. Additional dispersive dominant Raman modes that are probed by resonance Raman spectroscopy are observed. Additionally, iodinated graphene is probed by Kelvin probe force microscopy and by transport measurements showing p-doping surpassing non-covalent iodine doping by charge transfer-complex formation. The emergent Raman modes combined with strong p-doping indicate that iodine functionalization is distinct from simple iodine doping. A reaction mechanism based on these findings is proposed, identifying the large size of iodine atoms as the probable cause governing regiochemically controlled addition due to steric hinderance of reactive sites. The modification of the electronic structure is explained by the confinement of 1D trans-oligoene chains between sp3-defects. These results demonstrate the uniqueness of iodine reactivity toward graphene and the modification of the electronic structure of iodinated graphene, highlighting its dependence on the spatial arrangement of substituents.

Исследовано изменение интенсивности катодолюминесценции гексагонального нитрида бора в коротковолновой части спектра в процессе возбуждения электронным пучком. Показано, что интенсивность пика на длине волны 215 нм, связываемого с переходами зона–зона, убывает в процессе возбуждения электронами и стремится к стационарному значению, в то время как интенсивность пика на длине волны 320 нм возрастает под действием электронного облучения. Эта полоса, вероятно, обусловлена образованием центров люминесценции под действием электронного облучения.

Transition metal dichalcogenides (TMDCs) are often mechanically exfoliated on mica and examined under ambient conditions. It is known that above a certain relative humidity, a molecularly thin layer of water intercalates between the mica and the TMDC. Herein, the effect of molecularly thin liquid layers on the optical spectra of MoS 2 and WS 2 exfoliated on dry mica and exposed to the vapors of water, ethanol, and tetrahydrofuran (THF) is investigated. Photoluminescence and differential reflectance (Δ R / R ) spectra on the TMDCs on dry mica show dominant trion emission due to n‐doping. Intercalation of water removes charge doping and results in purely neutral exciton emission, while an ethanol layer, which can be reversibly exchanged with water, does not completely suppress charge. Similarly, THF intercalates between TMDC and mica, as shown by atomic force microscopy, but it does not suppress the charging of mica. In MoS 2 bi‐ and trilayers, an intercalated water layer leads to a near doubling of the intensity of the indirect band transition. The described charging/discharging of TMDCs by molecular thin liquid layers can provide important clues to better control the optical properties of TMDCs under environmental conditions.