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Abstract Focusing on Rhenium disulfide (ReS2), a group VII transition metal di-chalcogenides (TMDC), being a promising contender system for future nanoelectronics and optoelectronics, here, we present an innovative pathway to experimentally achieve an almost barrier-free contact for the ReS2 field effect transistors (FETs) by using few layered graphene as contact electrodes, further supported by comparative first-principles analysis. Such barrier-free contacts enable the observation of metal-to-insulator transition with enhanced room temperature carrier mobility up to 25 cm2/Vs, linear Ids-Vds characteristic down to 80 K, along with the reduction of 1/f noise by more than two orders of magnitude. We further demonstrate a highly responsive gate- tunable phototransistor (R > 106 A/W) at an illumination wavelength of 633 nm. This work demonstrates a straightforward strategy to unlock the full potential of ReS2 for CMOS compatible future electronic and optoelectronic devices.

Abstract Current semiconductor qubits rely either on the spin or on the charge degree of freedom to encode quantum information. By contrast, in bilayer graphene the valley degree of freedom, stemming from the crystal lattice symmetry, is a robust quantum number that can therefore be harnessed for this purpose. The simplest implementation of a valley qubit would rely on two states with opposite valleys as in the case of a single-carrier bilayer graphene quantum dot immersed in a small perpendicular magnetic field (B ⊥ ≲ 100 mT). However, the single-carrier quantum dot excited states spectrum has not been resolved to date in the relevant magnetic field range. Here, we fill this gap, by measuring the parallel and perpendicular magnetic field dependence of this spectrum with an unprecedented resolution of 4 μeV. We use a time-resolved charge detection technique that gives us access to individual tunnel events. Our results come as a direct verification of the predicted spectrum and establish a new upper-bound on inter-valley mixing, equal to our energy resolution. Our charge detection technique opens the door to measuring the relaxation time of a valley qubit in a single-carrier bilayer graphene quantum dot.

Abstract Neuromorphic computing has emphasized the need for memristors with non-volatile, multiple conductance levels. This paper demonstrates the potential of hexagonal boron nitride (hBN)/graphene heterostructures to act as memristors with multiple resistance states that can be optically tuned using visible light. The number of resistance levels in graphene can be controlled by modulating doping levels, achieved by varying the electric field strength or adjusting the duration of optical illumination. Our measurements show that this photodoping of graphene results from the optical excitation of charge carriers from the nitrogen-vacancy levels of hBN to its conduction band, with these carriers then being transferred to graphene by the gate-induced electric field. We develop a qualitative model to describe our observations. Additionally, utilizing our device architecture, we propose a memristive crossbar array for vector-matrix multiplications.

Abstract Van der Waals heterostructures provide a versatile platform for tailoring electronic properties through the integration of two-dimensional materials. Among these combinations, the interaction between bilayer graphene and transition metal dichalcogenides (TMDs) stands out due to its potential for inducing spin–orbit coupling (SOC) in graphene. Future devices concepts require the understanding of the precise nature of SOC in TMD/bilayer graphene heterostructures and its influence on electronic transport phenomena. Here, we experimentally confirm the presence of two distinct types of SOC – Ising (Δ I = 1.55 meV) and Rashba (Δ R = 2.5 meV) – in bilayer graphene when interfaced with molybdenum disulfide. Furthermore, we reveal a non-monotonic trend in conductivity with respect to the electric displacement field at charge neutrality. This phenomenon is ascribed to the existence of single-particle gaps induced by the Ising SOC, which can be closed by a critical displacement field. Our findings also unveil sharp peaks in the magnetoconductivity around the critical displacement field, challenging existing theoretical models.

Abstract The stacking order and twist angle provide abundant opportunities for engineering band structures of two-dimensional materials, including the formation of moiré bands, flat bands, and topologically nontrivial bands. The inversion symmetry breaking in rhombohedral-stacked transitional metal dichalcogenides endows them with an interfacial ferroelectricity associated with an out-of-plane electric polarization. By utilizing twist angle as a knob to construct rhombohedral-stacked transitional metal dichalcogenides, antiferroelectric domain networks with alternating out-of-plane polarization can be generated. Here, we demonstrate that such spatially periodic ferroelectric polarizations in parallel-stacked twisted WSe2 can imprint their moiré potential onto a remote bilayer graphene. This remote moiré potential gives rise to pronounced satellite resistance peaks besides the charge-neutrality point in graphene, which are tunable by the twist angle of WSe2. Our observations of ferroelectric hysteresis at finite displacement fields suggest the moiré is delivered by a long-range electrostatic potential. The constructed superlattices by moiré ferroelectricity represent a highly flexible approach, as they involve the separation of the moiré construction layer from the electronic transport layer. This remote moiré is identified as a weak potential and can coexist with conventional moiré. Our results offer a comprehensive strategy for engineering band structures and properties of two-dimensional materials by utilizing moiré ferroelectricity.

Objectives: To date, there have been no reports on the long-term effects of a method that combines external hemorrhoidectomy with aluminum potassium sulfate and tannic acid (ALTA) sclerotherapy. This study aimed to investigate the efficacy and safety of external hemorrhoidectomy combined with ALTA sclerotherapy (EA) in reducing postoperative complications associated with conventional hemorrhoidectomy. Methods: EA was performed under sacral epidural anesthesia, and ALTA sclerotherapy was applied to the remaining internal hemorrhoids after resection of the external hemorrhoids. Mixed internal and external hemorrhoids were treated with EA, whereas internal hemorrhoids without external hemorrhoids were treated with ALTA sclerotherapy. The three EA patterns were defined as EA1, EA2, and EA3, depending on the number of EAs performed. Results: This study included 3,403 patients who underwent EA for grade II-IV mixed hemorrhoids. EA1 was the most common, with 1,789 (52.6%) cases, followed by EA2 (36.2%) and EA3 (11.2%). Postoperative complications occurred in 120 (3.5%) patients and increased with the number of EAs, with fever and bleeding being common in the early postoperative period, and perianal abscess and/or fistula being common after 1 month. The mean postoperative follow-up period was 26.4 months, and 136 (4.0%) patients underwent reoperation for recurrent internal or mixed hemorrhoids. The reoperation rate for EA1 was significantly higher than that for EA2 and EA3. The 5- and 10-year cumulative recurrence-free rates were 92.5% and 67.2%, respectively. Conclusions: EA is as curative as conventional hemorrhoidectomy and reduces postoperative complications. Therefore, EA is the preferred procedure for patients with mixed hemorrhoids.

Abstract One of the most captivating properties of polaritons is their capacity to confine light at the nanoscale. This confinement is even more extreme in two-dimensional (2D) materials. 2D polaritons have been investigated by optical measurements using an external photodetector. However, their effective spectrally resolved electrical detection via far-field excitation remains unexplored. This hinders their exploitation in crucial applications such as sensing, hyperspectral imaging, and optical spectrometry, banking on their potential for integration with silicon technologies. Herein, we present the electrical spectroscopy of polaritonic nanoresonators based on a high-quality 2D-material heterostructure, which serves at the same time as the photodetector and the polaritonic platform. Subsequently, we electrically detect these mid-infrared resonators by near-field coupling to a graphene pn-junction. The nanoresonators simultaneously exhibit extreme lateral confinement and high-quality factors. This work opens a venue for investigating this tunable and complex hybrid system and its use in compact sensing and imaging platforms.

Abstract Fractional quantum Hall (FQH) phases emerge due to strong electronic interactions and are characterized by anyonic quasiparticles, each distinguished by unique topological parameters, fractional charge, and statistics. In contrast, the integer quantum Hall (IQH) effects can be understood from the band topology of non-interacting electrons. We report a surprising super-universality of the critical behavior across all FQH and IQH transitions. Contrary to the anticipated state-dependent critical exponents, our findings reveal the same critical scaling exponent κ = 0.41 ± 0.02 and localization length exponent γ = 2.4 ± 0.2 for fractional and integer quantum Hall transitions. From these, we extract the value of the dynamical exponent z ≈ 1. We have achieved this in ultra-high mobility trilayer graphene devices with a metallic screening layer close to the conduction channels. The observation of these global critical exponents across various quantum Hall phase transitions was masked in previous studies by significant sample-to-sample variation in the measured values of κ in conventional semiconductor heterostructures, where long-range correlated disorder dominates. We show that the robust scaling exponents are valid in the limit of short-range disorder correlations.

The liver is a complex organ with a highly organized structure in which tight junctions (TJs) play an important role in maintaining their function by regulating barrier properties and cellular polarity. Dysfunction of TJs is associated with liver diseases, including progressive familial intrahepatic cholestasis (PFIC). In this study, we investigated the molecular alterations in a liver-specific ZO-1 and ZO-2 double-knockout (DKO) mouse model, which exhibits features resembling those of PFIC4 patients with mutations in the ZO-2 gene. RNA-seq analysis revealed the upregulation of genes involved in the oxidative stress response, xenobiotic metabolism, and cholesterol metabolism in DKO livers. Conversely, the expression of genes regulated by HNF4α was lower in DKO livers than in the wild-type controls. Furthermore, age-associated analysis elucidated the timing and progression of these pathway changes as well as alterations in molecules related to TJs and apical polarity. Our research uncovered previously unknown implications of ZO-1 and ZO-2 in liver physiology and provides new insights into the molecular pathogenesis of PFIC4 and other tight junction-related liver diseases. These findings contribute to a better understanding of the complex mechanisms underlying liver function and dysfunction and may lead to the development of novel therapeutic strategies for liver diseases associated with tight junction impairment. Key words: tight junctions, ZO-1/ZO-2 knockout mouse, liver, transcriptome analysis, molecular pathological progression

Abstract Moiré structures formed by twisting three layers of graphene with two independent twist angles present an ideal platform for studying correlated quantum phenomena, as an infinite set of angle pairs is predicted to exhibit flat bands. Moreover, the two mutually incommensurate moiré patterns among the twisted trilayer graphene (TTG) can form highly tunable moiré quasicrystals. This enables us to extend correlated physics in periodic moiré crystals to quasiperiodic systems. However, direct local characterization of the structure of the moiré quasicrystals and of the resulting flat bands are still lacking, which is crucial to fundamental understanding and control of the correlated moiré physics. Here, we demonstrate the existence of flat bands in a series of TTGs with various twist angle pairs and show that the TTGs with different magic angle pairs are strikingly dissimilar in their atomic and electronic structures. The lattice relaxation and the interference between moiré patterns are highly dependent on the twist angles. Our direct spatial mappings, supported by theoretical calculations, reveal that the localization of the flat bands exhibits distinct symmetries in different regions of the moiré quasicrystals.

Abstract Graphene placed on hexagonal boron nitride (hBN) has received significant interest due to its excellent electrical performance and physics phenomena, such as superlattice Dirac points. Direct molecular beam epitaxy growth of graphene on hBN offers an alternative fabrication route for hBN/graphene devices. Here, we investigate the electronic transport of moiré field effect transistors (FETs) in which the conducting channel is monolayer graphene grown on hexagonal boron nitride by high temperature molecular beam epitaxy (HT-MBE). Alignment between hBN and HT-MBE graphene crystal lattices gives rise to a moiré-fringed hexagonal superlattice pattern. Its electronic band structure takes the form of a “Hofstadter butterfly”. When a strong magnetic field B is applied perpendicular to the graphene layer, the electrical conductance displays magneto-oscillations, periodic in B −1, over a wide range of gate voltages and temperatures up to 350 K. We attribute this behaviour to the quantisation of electronic charge and magnetic flux within each unit cell of the superlattice, which gives rise to so-called Brown-Zak oscillations, previously reported only in high-mobility exfoliated graphene. Thus, this HT-MBE graphene/hBN heterostructure provides a platform for observation of room temperature quantum effects and device applications.

Abstract Floquet engineering is a promising tool to manipulate quantum systems coherently. A well-known example is the optical Stark effect, which has been used for optical trapping of atoms and breaking time-reversal symmetry in solids. However, as a coherent nonlinear optical effect, Floquet engineering typically requires high field intensities obtained in ultrafast pulses, severely limiting its use. Here, we demonstrate using cavity engineering of the vacuum modes to achieve orders-of-magnitude enhancement of the effective Floquet field, enabling Floquet effects at an extremely low fluence of 450 photons/μm2. At higher fluences, the cavity-enhanced Floquet effects lead to 50 meV spin and valley splitting of WSe2 excitons, corresponding to an enormous time-reversal breaking, non-Maxwellian magnetic field of over 200 T. Utilizing such an optically controlled effective magnetic field, we demonstrate an ultrafast, picojoule chirality XOR gate. These results suggest that cavity-enhanced Floquet engineering may enable the creation of steady-state or quasi-equilibrium Floquet bands, strongly non-perturbative modifications of materials beyond the reach of other means, and application of Floquet engineering to a wide range of materials and applications.

Abstract Interfacial ferroelectricity, prevalent in various parallel-stacked layered materials, allows switching of out-of-plane ferroelectric order by in-plane sliding of adjacent layers. Its resilience against doping potentially enables next-generation storage and logic devices. However, studies have been limited to indirect sensing or visualization of ferroelectricity. For transition metal dichalcogenides, there is little knowledge about the influence of ferroelectric order on their intrinsic valley and excitonic properties. Here, we report direct probing of ferroelectricity in few-layer 3R-MoS2 using reflectance contrast spectroscopy. Contrary to a simple electrostatic perception, layer-hybridized excitons with out-of-plane electric dipole moment remain decoupled from ferroelectric ordering, while intralayer excitons with in-plane dipole orientation are sensitive to it. Ab initio calculations identify stacking-specific interlayer hybridization leading to this asymmetric response. Exploiting this sensitivity, we demonstrate optical readout and control of multi-state polarization with hysteretic switching in a field-effect device. Time-resolved Kerr ellipticity reveals direct correspondence between spin-valley dynamics and stacking order.

Abstract Doped van der Waals heterostructures host layer-hybridized trions, i.e. charged excitons with layer-delocalized constituents holding promise for highly controllable optoelectronics. Combining a microscopic theory with photoluminescence (PL) experiments, we demonstrate the electrical tunability of the trion energy landscape in naturally stacked WSe2 bilayers. We show that an out-of-plane electric field modifies the energetic ordering of the lowest lying trion states, which consist of layer-hybridized $$\Lambda$$ Λ -point electrons and layer-localized K-point holes. At small fields, intralayer-like trions yield distinct PL signatures in opposite doping regimes characterized by weak Stark shifts in both cases. Above a doping-asymmetric critical field, interlayer-like species are energetically favored and produce PL peaks with a pronounced Stark red-shift and a counter-intuitively large intensity arising from efficient phonon-assisted recombination. Our work presents an important step forward in the microscopic understanding of layer-hybridized trions in van der Waals heterostructures and paves the way towards optoelectronic applications based on electrically controllable atomically-thin semiconductors.

Abstract Atomically thin semiconductor heterostructures provide a two-dimensional (2D) device platform for creating high densities of cold, controllable excitons. Interlayer excitons (IEs), bound electrons and holes localized to separate 2D quantum well layers, have permanent out-of-plane dipole moments and long lifetimes, allowing their spatial distribution to be tuned on demand. Here, we employ electrostatic gates to trap IEs and control their density. By electrically modulating the IE Stark shift, electron-hole pair concentrations above 2 × 1012 cm−2 can be achieved. At this high IE density, we observe an exponentially increasing linewidth broadening indicative of an IE ionization transition, independent of the trap depth. This runaway threshold remains constant at low temperatures, but increases above 20 K, consistent with the quantum dissociation of a degenerate IE gas. Our demonstration of the IE ionization in a tunable electrostatic trap represents an important step towards the realization of dipolar exciton condensates in solid-state optoelectronic devices.

Abstract Spin-polarized light-emitting diodes (spin-LEDs) convert the electronic spin information to photon circular polarization, offering potential applications including spin amplification, optical communications, and advanced imaging. The conventional control of the emitted light’s circular polarization requires a change in the external magnetic field, limiting the operation conditions of spin-LEDs. Here, we demonstrate an atomically thin spin-LED device based on a heterostructure of a monolayer WSe2 and a few-layer antiferromagnetic CrI3, separated by a thin hBN tunneling barrier. The CrI3 and hBN layers polarize the spin of the injected carriers into the WSe2. With the valley optical selection rule in the monolayer WSe2, the electroluminescence exhibits a high degree of circular polarization that follows the CrI3 magnetic states. Importantly, we show an efficient electrical tuning, including a sign reversal, of the electroluminescent circular polarization by applying an electrostatic field due to the electrical tunability of the few-layer CrI3 magnetization. Our results establish a platform to achieve on-demand operation of nanoscale spin-LED and electrical control of helicity for device applications.

Background: Periodontal disease is the leading cause of tooth loss, and an association between periodontal disease and non-oral systemic diseases has been shown. Formation of biofilm by periodontal pathogens such as Fusobacterium nucleatum, Porphyromonas gingivalis, and Streptococcus mutans and their resistance to antimicrobial agents are at the root of persistent and chronic bacterial infections. Methods: The bactericidal effect of far-ultraviolet (F-UV) light irradiation at 222 nm on periodontal bacteria was assessed qualitatively and quantitatively. The effect of biofilm disruption by F-UV light on periodontal bacteria was examined by crystal violet staining, and the morphologic changes of the biofilm after F-UV irradiation were explored by confocal laser microscopy and scanning electron microscopy. We developed a thin fiber-type 222 nm F-UV irradiator and studied its safety and effect of reducing bacteria in rodent models. Results: F-UV light at 222 nm had a bactericidal effect on F. nucleatum, P. gingivalis, and S. mutans. Irradiation with F-UV light reduced the biofilm formed by the bacteria and sterilized them from within. Confocal laser microscopy showed a clear reduction in biofilm thickness, and scanning electron microscopy confirmed disintegration of the biofilm architecture. F-UV irradiation was less damaging to DNA and less cytotoxic than deep-ultraviolet light, and it reduced bacterial counts on the tooth surface. Conclusion: F-UV irradiation has the potential to destroy biofilm and act as a bactericide against pathogenic bacteria in the biofilm.

Abstract Electronic interferometers using the chiral, one-dimensional (1D) edge channels of the quantum Hall effect (QHE) can demonstrate a wealth of fundamental phenomena. The recent observation of phase jumps in a Fabry-Pérot (FP) interferometer revealed anyonic quasiparticle exchange statistics in the fractional QHE. When multiple integer edge channels are involved, FP interferometers have exhibited anomalous Aharonov-Bohm (AB) interference frequency doubling, suggesting putative pairing of electrons into $${{\boldsymbol{2}}}{{\boldsymbol{e}}}$$ 2 e quasiparticles. Here, we use a highly tunable graphene-based QHE FP interferometer to observe the connection between interference phase jumps and AB frequency doubling, unveiling how strong repulsive interaction between edge channels leads to the apparent pairing phenomena. By tuning electron density in-situ from filling factor $${{\boldsymbol{\nu }}} \, < \, {{\boldsymbol{2}}}$$ ν < 2 to $${{\boldsymbol{\nu }}} \, > \, {{\boldsymbol{7}}}$$ ν > 7 , we tune the interaction strength and observe periodic interference phase jumps leading to AB frequency doubling. Our observations demonstrate that the combination of repulsive interaction between the spin-split $${{\boldsymbol{\nu }}}={{\boldsymbol{2}}}$$ ν = 2 edge channels and charge quantization is sufficient to explain the frequency doubling, through a near-perfect charge screening between the localized and extended edge channels. Our results show that interferometers are sensitive probes of microscopic interactions and enable future experiments studying correlated electrons in 1D channels using density-tunable graphene.

Abstract In Bernal-stacked bilayer graphene (BBG), the Landau levels give rise to an intimate connection between valley and layer degrees of freedom. Adding a moiré superlattice potential enriches the BBG physics with the formation of topological minibands — potentially leading to tunable exotic quantum transport. Here, we present magnetotransport measurements of a high-quality bilayer graphene–hexagonal boron nitride (hBN) heterostructure. The zero-degree alignment generates a strong moiré superlattice potential for the electrons in BBG and the resulting Landau fan diagram of longitudinal and Hall resistance displays a Hofstadter butterfly pattern with a high level of detail. We demonstrate that the intricate relationship between valley and layer degrees of freedom controls the topology of moiré-induced bands, significantly influencing the energetics of interacting quantum phases in the BBG superlattice. We further observe signatures of field-induced correlated insulators, helical edge states and clear quantizations of interaction-driven topological quantum phases, such as symmetry broken Chern insulators.

Abstract Fractional quantum Hall (FQH) states are exotic quantum many-body phases whose elementary charged excitations are anyons obeying fractional braiding statistics. While most FQH states are believed to have Abelian anyons, the Moore–Read type states with even denominators – appearing at half filling of a Landau level (LL) – are predicted to possess non-Abelian excitations with appealing potential in topological quantum computation. These states, however, depend sensitively on the orbital contents of the single-particle LL wavefunctions and the LL mixing. Here we report magnetotransport measurements on Bernal-stacked trilayer graphene, whose multiband structure facilitates interlaced LL mixing, which can be controlled by external magnetic and displacement fields. We observe robust FQH states including even-denominator ones at filling factors ν = − 9/2, − 3/2, 3/2 and 9/2. In addition, we fine-tune the LL mixing and crossings to drive quantum phase transitions of these half-filling states and neighbouring odd-denominator ones, exhibiting related emerging and waning behaviour.

Abstract Defect centers in wide-band-gap crystals have garnered interest for their potential in applications among optoelectronic and sensor technologies. However, defects embedded in highly insulating crystals, like diamond, silicon carbide, or aluminum oxide, have been notoriously difficult to excite electrically due to their large internal resistance. To address this challenge, we realized a new paradigm of exciting defects in vertical tunneling junctions based on carbon centers in hexagonal boron nitride (hBN). The rational design of the devices via van der Waals technology enabled us to raise and control optical processes related to defect-to-band and intradefect electroluminescence. The fundamental understanding of the tunneling events was based on the transfer of the electronic wave function amplitude between resonant defect states in hBN to the metallic state in graphene, which leads to dramatic changes in the characteristics of electrons due to different band structures of constituent materials. In our devices, the decay of electrons via tunneling pathways competed with radiative recombination, resulting in an unprecedented degree of tuneability of carrier dynamics due to the significant sensitivity of the characteristic tunneling times on the thickness and structure of the barrier. This enabled us to achieve a high-efficiency electrical excitation of intradefect transitions, exceeding by several orders of magnitude the efficiency of optical excitation in the sub-band-gap regime. This work represents a significant advancement towards a universal and scalable platform for electrically driven devices utilizing defect centers in wide-band-gap crystals with properties modulated via activation of different tunneling mechanisms at a level of device engineering.

Abstract Phonon dispersion in crystals determines many important material properties, but its measurement usually requires large-scale facilities and is limited to bulk samples. Here, we demonstrate the measurement of full phonon dispersion along the stacking direction in nanoscale systems by using picosecond acoustics. A heterostructure sample was prepared consisting of layers of hexagonal boron nitride (hBN) sandwiching a thin layer of black phosphorus (BP), within which a strain pulse was generated by photoexcitation and observed with an optical probe in the BP layer. The strain pulse traverses to the few nanometer thick hBN layers, where it propagates to the edge and echoes back, like acoustic waves in Newton’s cradle. The echoes returning to the BP layer provide information on the frequency-dependent time-of-flight and group velocity dispersion of the sample system. The microscopic origin of the photoinduced strain pulse generation and its propagation is revealed from first principles. Phonon frequency combs observed in the Fourier transform spectrum confirm the strain wave round trips and demonstrate the feasibility of determining group velocity dispersion through photoacoustics.

Abstract Excitons, pairs of electrons and holes, undergo a Bose-Einstein condensation at low temperatures. An important platform to study excitons is double-layer two-dimensional electron gases, with two parallel planes of electrons and holes separated by a thin insulating layer. Lowering this separation (d) strengthens the exciton binding energy, however, leads to the undesired interlayer tunneling, resulting in annihilation of excitons. Here, we report the observation of a sequences of robust exciton condensates (ECs) in double bilayer graphene twisted to ~ 10° with no insulating mid-layer. The large momentum mismatch between two graphene layers suppresses interlayer tunneling, reaching a d ~ 0.334 nm. Measuring the bulk and edge transport, we find incompressible states corresponding to ECs when both layers are in half-filled N = 0, 1 Landau levels (LLs). Theoretical calculations suggest that the low-energy charged excitation of ECs can be meron-antimeron or particle-hole pair, which relies on both LL index and carrier type. Our results establish a novel platform with extreme coupling strength for studying quantum bosonic phase.

Abstract Magnetism in two-dimensional materials reveals phenomena distinct from bulk magnetic crystals, with sensitivity to charge doping and electric fields in monolayer and bilayer van der Waals magnet CrI3. Within the class of layered magnets, semiconducting CrSBr stands out by featuring stability under ambient conditions, correlating excitons with magnetic order and thus providing strong magnon-exciton coupling, and exhibiting peculiar magneto-optics of exciton-polaritons. Here, we demonstrate that both exciton and magnetic transitions in bilayer and trilayer CrSBr are sensitive to voltage-controlled field-effect charging, exhibiting bound exciton-charge complexes and doping-induced metamagnetic transitions. Moreover, we demonstrate how these unique properties enable optical probes of local magnetic order, visualizing magnetic domains of competing phases across metamagnetic transitions induced by magnetic field or electrostatic doping. Our work identifies few-layer CrSBr as a rich platform for exploring collaborative effects of charge, optical excitations, and magnetism.

Abstract The moiré potential serves as a periodic quantum confinement for optically generated excitons, creating spatially ordered zero-dimensional quantum systems. However, a broad emission spectrum resulting from inhomogeneity among moiré potentials hinders the investigation of their intrinsic properties. In this study, we demonstrated a method for the optical observation of quantum coherence and interference of a single moiré exciton in a twisted semiconducting heterobilayer beyond the diffraction limit of light. We observed a single and sharp photoluminescence peak from a single moiré exciton following nanofabrication. Our findings revealed the extended duration of quantum coherence in a single moiré exciton, persisting beyond 10 ps, and an accelerated decoherence process with increasing temperature and excitation power density. Moreover, quantum interference experiments revealed the coupling between moiré excitons in different moiré potential minima. The observed quantum coherence and interference of moiré exciton will facilitate potential applications of moiré quantum systems in quantum technologies.

Abstract Understanding the quantum transport properties of (Two‐dimensional) 2D perovskite heterostructures is key to interpreting their electronic performance and promoting optoelectronic devices. Here, it is shown that clear Shubnikov‐de Hass oscillation appears in the heterostructure of monocrystalline 2D perovskites and graphene, thanks to the clean interface. An efficient charge transfer between perovskite nanosheets and graphene is found, facilitating the separation of electrons and holes at the interface. The relation between the charge transfer efficiency and microscopic interface structures is quantitatively described. The evidence of photo‐assisted transport from the photo‐response of magnetoresistance is revealed, which happens between Landau levels of two graphene layers mediated by hot carriers in the perovskite layer, overcoming the barrier from the organic layers in the Ruddlesden‐Popper perovskite phase. These results provide a picture to understand the transport behavior of 2D perovskite/graphene heterostructure and a reference for the controlled design of interfaces in perovskite optoelectronic devices.

ObjectiveThe purpose of this study was to predict the four cold–heat patterns in patients who have the subjective symptoms of the cold–heat pattern described in the International Classification of Diseases Traditional Medicine Conditions – Module 1 by applying a machine learning algorithm.MethodsSubjects were first-visit Kampo outpatients at six institutions who agreed to participate in this multicenter prospective observational study. The cold pattern model and the heat pattern model were created separately with 148 symptoms, body mass index, blood pressure (systolic and diastolic), age, and sex. Along with a single cold or heat pattern, the tangled heat/cold pattern is defined as being predicted by both cold and heat patterns, while the moderate (heat/cold) pattern is defined as being predicted by neither the cold pattern nor the heat pattern.ResultsWe included 622 participants (mean age ±standard deviation, 54.4 ± 16.9; with female 501). The accuracy, macro-recall, precision, and F1-score of a combination of the two prediction models were 96.7%, 93.2%, 85.6%, and 88.5% respectively. The important items were compatible with the definitions of the cold–heat pattern.ConclusionWe developed a prediction model on cold–heat patterns with data from patients whose subjective cold/heat-related symptoms matched the cold–heat pattern diagnosis by the physician.

Abstract Two‐dimensional (2D) antiferromagnetic (AFM) semiconductors are promising components of opto‐spintronic devices due to terahertz operation frequencies and minimal interactions with stray fields. However, the lack of net magnetization significantly limits the number of experimental techniques available to study the relationship between magnetic order and semiconducting properties. Here, they demonstrate conditions under which photocurrent spectroscopy can be employed to study many‐body magnetic excitons in the 2D AFM semiconductor NiI2. The use of photocurrent spectroscopy enables the detection of optically dark magnetic excitons down to bilayer thickness, revealing a high degree of linear polarization that is coupled to the underlying helical AFM order of NiI2. In addition to probing the coupling between magnetic order and dark excitons, this work provides strong evidence for the multiferroicity of NiI2 down to bilayer thickness, thus demonstrating the utility of photocurrent spectroscopy for revealing subtle opto‐spintronic phenomena in the atomically thin limit.

Abstract At the interface of 2D heterostructures, the presence of defects and their manipulation play a crucial role in the interfacial charge transfer behavior, further influencing the device functionality and performance. In this study, the impact of deliberately introduced photo‐active defects in the h‐BN layer on the interfacial charge transfer and photoresponse performance of a metal‐insulator‐semiconductor type heterostructure device is explored. The formation and concentration of defects are qualitatively controlled using an inductive coupled plasma treatment method, as evidenced by enhanced h‐BN defect emission and more efficient optically induced doping of graphene at the graphene/h‐BN interface. Besides, the use of the h‐BN layer between graphene and WS2 not only suppresses charge carriers in the dark state, but also promotes the separation of photo‐generated electron‐hole pairs and interfacial charge transfer due to the existence of defect levels, leading to orders of magnitude improvement in the light on/off ratio and self‐driving performance of the heterostructure photodetector. This strategy of controlling defect states in the insulating layer provides a new approach to optimize the charge transfer processes at the 2D interfaces, so as to expand its potential applications in the fields of electronic and optoelectronic devices.

Abstract 2D van der Waals (vdW) magnets with layer‐dependent magnetic states and/or diverse magnetic interactions and anisotropies have attracted extensive research interest. Despite the advances, a notable challenge persists in effectively manipulating the tunneling anisotropic magnetoresistance (TAMR) of 2D vdW magnet‐based magnetic tunnel junctions (MTJs). Here, this study reports the novel and anomalous tunneling magnetoresistance (TMR) oscillations and pioneering demonstration of bias and gate voltage controllable TAMR in 2D vdW MTJs, utilizing few‐layer CrPS4. This material, inherently an antiferromagnet, transitions to a canted magnetic order upon application of external magnetic fields. Through TMR measurements, this work unveils the novel layer‐dependent oscillations in the tunneling resistance for few‐layer CrPS4 devices under both out‐of‐plane and in‐plane magnetic fields, with a pronounced controllability via gate voltage. Intriguingly, this study demonstrates that both the polarity and magnitude of TAMR in CrPS4 can be effectively tuned through either a bias or gate voltage. The mechanism behind this electrically tunable TAMR is further elucidated through first‐principles calculations. The implications of the findings are far‐reaching, providing new insights into 2D magnetism and opening avenues for the development of innovative spintronic devices based on 2D vdW magnets.

BackgroundAs the novel coronavirus disease 2019 (COVID-19) pandemic subsides, the clinical sequelae are becoming more problematic. Interestingly, the statistical data indicate that Africa has experienced the lowest number of cases and deaths, with an unexpected phenomenon where the number of deaths from COVID-19 has not increased significantly. Several studies have investigated the relationship between diet and coronavirus. However, no systematic review/meta-analysis has conclusively linked diet (phytochemicals and vitamin D) and the gut microbiota in the context of COVID-19.MethodsThis study examined the responses to COVID-19 in Japan and Africa, formulating the following hypotheses: (1) a healthy diet is effective against COVID-19, (2) blood vitamin D levels are associated with COVID-19 mortality, and (3) COVID-19 is associated with the gut microbiota. To investigate these hypotheses, a keyword search and meta-analysis were conducted using PubMed, and each hypothesis was tested.ResultsThis study found that a healthy diet, particularly rich in phytochemicals such as polyphenols and flavonoids, is effective against COVID-19. An association was detected between blood vitamin D levels and COVID-19 mortality. The gut microbiota was linked to COVID-19 and its amelioration. These findings may have significant implications for not only understanding COVID-19 but also future prevention of pneumonia.

Abstract This study explores defect engineering in 2D materials using ion beam irradiation to modify the electrical and optical properties with potential in advancing quantum electronics and photonics. Helium and neon ions ranging from 5 to 7.5 keV are employed to manipulate charge transport in monolayer molybdenum disulfide (MoS2). In situ electrical characterization occurs without vacuum breakage post‐irradiation. Raman and photoluminescence spectroscopy quantify ion irradiation's impact on MoS2. Small doses of helium ion irradiation enhance monolayer MoS2 conductivity in field‐effect transistor geometry by inducing doping and substrate charging. Findings reveal a strong correlation between the electrical properties of MoS2 and the primary ion used, as well as the substrate on which the irradiation occurred. Using hexagonal boron nitride (h‐BN) as a buffer layer between MoS2 flake and SiO2 substrate yields distinct alterations in electrical behavior subsequent to ion irradiation compared to the MoS2 layer directly interfacing with SiO2. Molecular dynamics simulations and density functional theory provide insight into experimental results, emphasizing substrate influence on measured electrical properties post‐ion irradiation.

IntroductionIn traditional Japanese Kampo medicine, a profound anamnesis is completed by clinical examination. The resulting clinical image forms the basis of the patient’s diagnosis pattern, including the recent mental, physical, and social contexts. Kampo questionnaires support pattern diagnosis and bridge traditional and Western medicine diagnoses.Aims of the studyTraditional Kampo therapy is tailored to a specific body constitution, while Western medicine treatment is tailored to a specific disease. The aims of this study were to analyze whether traditional Kampo diagnosis is applicable to German patients and whether specific symptom patterns are characteristic for defined diseases.Material and methodsThis study validates for the first time a Kampo questionnaire adapted for German patients. The analysis focuses on patients with gastrointestinal diseases, the main field for Kampo medicines.ResultsIn total, we prospectively included 251 participants; of those, 58 were cancer patients (23.1%), 35 had Crohn’s disease (13.9%), 18 had ulcerative colitis (7.2%), 17 had irritable bowel syndrome (6.8%), and 103 had other abdominal diseases (41%), as well as 20 German controls (8%). The patient population consisted of 144 female (57.4%) and 107 male (42.6%) participants. The median age was 65 years. The disease duration (average: 211 months) varied from 1 month (cancer patient) to 540 months (patient with Crohn’s disease). The scores for questions on the state of mind were significantly higher in patients with inflammatory bowel disease (IBD) as well as irritable bowel syndrome (IBS)—in comparison to the tumor and control groups. This was reflected in questions about abdominal discomfort, appetite, fecal habits, and cold sensation. Accordingly, symptoms of Qi (i.e., vital energy) deficiency were mostly observed in patients with chronic diseases such as Crohn’s disease and ulcerative colitis. Defined symptom combinations did not reflect conventional Western diagnosis.ConclusionOur study results show that symptom patterns are independent of the underlying disease. They rather depict the individual patient within an individual time frame. Traditional Kampo questionnaires were found to be valid for the analysis of a patients’ body constitution (sho) and serve as a guide for Kampo treatment. We propose that individual pattern diagnosis should be taken into account to help treatment individualization.

Abstract Stark effect, the electric-field analogue of magnetic Zeeman effect, is one of the celebrated phenomena in modern physics and appealing for emergent applications in electronics, optoelectronics, as well as quantum technologies. While in condensed matter it has prospered only for excitons, whether other collective excitations can display Stark effect remains elusive. Here, we report the observation of phonon Stark effect in a two-dimensional quantum system of bilayer 2H-MoS2. The longitudinal acoustic phonon red-shifts linearly with applied electric fields and can be tuned over ~1 THz, evidencing giant Stark effect of phonons. Together with many-body ab initio calculations, we uncover that the observed phonon Stark effect originates fundamentally from the strong coupling between phonons and interlayer excitons (IXs). In addition, IX-mediated electro-phonon intensity modulation up to ~1200% is discovered for infrared-active phonon A 2u. Our results unveil the exotic phonon Stark effect and effective phonon engineering by IX-mediated mechanism, promising for a plethora of exciting many-body physics and potential technological innovations.

Abstract The semiconductors industry has put its eyes on two-dimensional (2D) materials produced by chemical vapour deposition (CVD) because they can be grown at the wafer level with small thickness fluctuations, which is necessary to build electronic devices and circuits. However, CVD-grown 2D materials can contain significant amounts of lattice distortions, which degrades the performance at the device level and increases device-to-device variability. Here we statistically analyse the quality of commercially available CVD-grown hexagonal boron nitride (h-BN) from the most popular suppliers. h-BN is of strategic importance because it is one of the few insulating 2D materials, and can be used as anti-scattering substrate and gate dielectric. We find that the leakage current and electrical homogeneity of all commercially available CVD h-BN samples are significantly worse than those of mechanically exfoliated h-BN of similar thickness. Moreover, in most cases the properties of the CVD h-BN samples analysed don’t match the technical specifications given by the suppliers, and the sample-to-sample variability is unsuitable for the reproducible fabrication of capacitors, transistors or memristors in different batches. In the short term, suppliers should try to provide accurate sample specifications matching the properties of the commercialized materials, and researchers should keep such inaccuracies in mind; and in the middle term suppliers should try to reduce the density of defects to enable the fabrication of high-performance devices with high reliability and reproducibility.

Abstract The in-plane anisotropy of electrical conductance in two-dimensional materials has garnered significant attention due to its potential in emerging device applications, offering an additional dimension to control carrier transport in 2D devices. However, previous research has primarily focused on the anisotropy within electrical channel, neglecting the significant impact of anisotropic electrical contacts of 2D materials. Here, we investigate anisotropic charge transport at the metal contacts of hBN-encapsulated ReS2 using edge-contacted Field Effect Transistors. We observed the marked difference in contact resistance between the cross-b and b directions, suggesting that charge transport from the metal to ReS2 is more efficient along the b direction. This difference in efficiency results in a substantial contact anisotropy, reaching ~70 at 77 K. Our findings indicate that the measured Schottky Barrier Height along the b direction is ~35 meV, which is smaller than along the cross-b direction. Moreover, the tunneling probability along the b direction is two times larger than along the cross-b direction. Our results indicate that both Schottky Barrier Height and tunneling amplitude are the primary contributors to the high contact anisotropy of ReS2. This work provides a valuable guideline for understanding how in-plane orientation influences charge transport at metallic contacts in 2D devices.

Abstract The fundamental properties of an exciton are determined by the spin, valley, energy, and spatial wavefunctions of the Coulomb-bound electron and hole. In van der Waals materials, these attributes can be widely engineered through layer stacking configuration to create highly tunable interlayer excitons with static out-of-plane electric dipoles, at the expense of the strength of the oscillating in-plane dipole responsible for light-matter coupling. Here we show that interlayer excitons in bi- and tri-layer 2H-MoSe2 crystals exhibit electric-field-driven coupling with the ground (1s) and excited states (2s) of the intralayer A excitons. We demonstrate that the hybrid states of these distinct exciton species provide strong oscillator strength, large permanent dipoles (up to 0.73 ± 0.01 enm), high energy tunability (up to ~200 meV), and full control of the spin and valley characteristics such that the exciton g-factor can be manipulated over a large range (from −4 to +14). Further, we observe the bi- and tri-layer excited state (2s) interlayer excitons and their coupling with the intralayer excitons states (1s and 2s). Our results, in good agreement with a coupled oscillator model with spin (layer)-selectivity and beyond standard density functional theory calculations, promote multilayer 2H-MoSe2 as a highly tunable platform to explore exciton-exciton interactions with strong light-matter interactions.

Abstract The flat bands in magic-angle twisted bilayer graphene (MATBG) provide an especially rich arena to investigate interaction-driven ground states. While progress has been made in identifying the correlated insulators and their excitations at commensurate moiré filling factors, the spin-valley polarizations of the topological states that emerge at high magnetic field remain unknown. Here we introduce a technique based on twist-decoupled van der Waals layers that enables measurement of their electronic band structure and–by studying the backscattering between counter-propagating edge states–the determination of the relative spin polarization of their edge modes. We find that the symmetry-broken quantum Hall states that extend from the charge neutrality point in MATBG are spin unpolarized at even integer filling factors. The measurements also indicate that the correlated Chern insulator emerging from half filling of the flat valence band is spin unpolarized and suggest that its conduction band counterpart may be spin polarized.

Abstract Excitons in two-dimensional (2D) semiconductors have offered an attractive platform for optoelectronic and valleytronic devices. Further realizations of correlated phases of excitons promise device concepts not possible in the single particle picture. Here we report tunable exciton “spin” orders in WSe2/WS2 moiré superlattices. We find evidence of an in-plane (xy) order of exciton “spin”—here, valley pseudospin—around exciton filling v ex = 1, which strongly suppresses the out-of-plane “spin” polarization. Upon increasing v ex or applying a small magnetic field of ~10 mT, it transitions into an out-of-plane ferromagnetic (FM-z) spin order that spontaneously enhances the “spin” polarization, i.e., the circular helicity of emission light is higher than the excitation. The phase diagram is qualitatively captured by a spin-1/2 Bose–Hubbard model and is distinct from the fermion case. Our study paves the way for engineering exotic phases of matter from correlated spinor bosons, opening the door to a host of unconventional quantum devices.

Abstract Semiconductor heterojunctions are ubiquitous components of modern electronics. Their properties depend crucially on the band alignment at the interface, which may exhibit straddling gap (type-I), staggered gap (type-II) or broken gap (type-III). The distinct characteristics and applications associated with each alignment make it highly desirable to switch between them within a single material. Here we demonstrate an electrically tunable transition between type-I and type-II band alignments in MoSe2/WS2 heterobilayers by investigating their luminescence and photocurrent characteristics. In their intrinsic state, these heterobilayers exhibit a type-I band alignment, resulting in the dominant intralayer exciton luminescence from MoSe2. However, the application of a strong interlayer electric field induces a transition to a type-II band alignment, leading to pronounced interlayer exciton luminescence. Furthermore, the formation of the interlayer exciton state traps free carriers at the interface, leading to the suppression of interlayer photocurrent and highly nonlinear photocurrent-voltage characteristics. This breakthrough in electrical band alignment control, interlayer exciton manipulation, and carrier trapping heralds a new era of versatile optical and (opto)electronic devices composed of van der Waals heterostructures.

Abstract Twisted bilayer graphene (tBLG) provides a fascinating platform for engineering flat bands and inducing correlated phenomena. By designing the stacking architecture of graphene layers, twisted multilayer graphene can exhibit different symmetries with rich tunability. For example, in twisted monolayer-bilayer graphene (tMBG) which breaks the C 2z symmetry, transport measurements reveal an asymmetric phase diagram under an out-of-plane electric field, exhibiting correlated insulating state and ferromagnetic state respectively when reversing the field direction. Revealing how the electronic structure evolves with electric field is critical for providing a better understanding of such asymmetric field-tunable properties. Here we report the experimental observation of field-tunable dichotomic electronic structure of tMBG by nanospot angle-resolved photoemission spectroscopy (NanoARPES) with operando gating. Interestingly, selective enhancement of the relative spectral weight contributions from monolayer and bilayer graphene is observed when switching the polarity of the bias voltage. Combining experimental results with theoretical calculations, the origin of such field-tunable electronic structure, resembling either tBLG or twisted double-bilayer graphene (tDBG), is attributed to the selectively enhanced contribution from different stacking graphene layers with a strong electron-hole asymmetry. Our work provides electronic structure insights for understanding the rich field-tunable physics of tMBG.

Abstract Effective control of magnetic phases in two-dimensional magnets would constitute crucial progress in spintronics, holding great potential for future computing technologies. Here, we report a new approach of leveraging tunneling current as a tool for controlling spin states in CrI3. We reveal that a tunneling current can deterministically switch between spin-parallel and spin-antiparallel states in few-layer CrI3, depending on the polarity and amplitude of the current. We propose a mechanism involving nonequilibrium spin accumulation in the graphene electrodes in contact with the CrI3 layers. We further demonstrate tunneling current-tunable stochastic switching between multiple spin states of the CrI3 tunnel devices, which goes beyond conventional bi-stable stochastic magnetic tunnel junctions and has not been documented in two-dimensional magnets. Our findings not only address the existing knowledge gap concerning the influence of tunneling currents in controlling the magnetism in two-dimensional magnets, but also unlock possibilities for energy-efficient probabilistic and neuromorphic computing.

Abstract Moiré superlattices of transition metal dichalcogenides offer a unique platform to explore correlated exciton physics with optical spectroscopy. Whereas the spatially modulated potentials evoke that the exciton resonances are distinct depending on a site in a moiré supercell, there have been no clear demonstration how the moiré excitons trapped in different sites dynamically interact with the doped carriers; so far the exciton-electron dynamic interactions were presumed to be site-dependent. Thus, the transient emergence of nonequilibrium correlations are open questions, but existing studies are limited to steady-state optical measurements. Here we report experimental fingerprints of site-dependent exciton correlations under continuous-wave as well as ultrashort optical excitations. In near-zero angle-aligned WSe2/WS2 heterobilayers, we observe intriguing polarization switching and strongly enhanced Pauli blocking near the Mott insulating state, dictating the dominant correlation-driven effects. When the twist angle is near 60°, no such correlations are observed, suggesting the strong dependence of atomic registry in moiré supercell configuration. Our studies open the door to largely unexplored nonequilibrium correlations of excitons in moiré superlattices.

Abstract The discovery of various primary ferroic phases in atomically-thin van der Waals crystals have created a new two-dimensional wonderland for exploring and manipulating exotic quantum phases. It may also bring technical breakthroughs in device applications, as evident by prototypical functionalities of giant tunneling magnetoresistance, gate-tunable ferromagnetism and non-volatile ferroelectric memory etc. However, two-dimensional multiferroics with effective magnetoelectric coupling, which ultimately decides the future of multiferroic-based information technology, has not been realized yet. Here, we show that an unconventional magnetoelectric coupling mechanism interlocked with heterogeneous ferrielectric transitions emerges at the two-dimensional limit in van der Waals multiferroic CuCrP2S6 with inherent antiferromagnetism and antiferroelectricity. Distinct from the homogeneous antiferroelectric bulk, thin-layer CuCrP2S6 under external electric field makes layer-dependent heterogeneous ferrielectric transitions, minimizing the depolarization effect introduced by the rearrangements of Cu+ ions within the ferromagnetic van der Waals cages of CrS6 and P2S6 octahedrons. The resulting ferrielectric phases are characterized by substantially reduced interlayer magnetic coupling energy of nearly 50% with a moderate electric field of 0.3 V nm−1, producing widely-tunable magnetoelectric coupling which can be further engineered by asymmetrical electrode work functions.

Abstract Bernal bilayer graphene (BLG) offers a highly flexible platform for tuning the band structure, featuring two distinct regimes. One is a tunable band gap induced by large displacement fields. Another is a gapless metallic band occurring at low fields, featuring rich fine structure consisting of four linearly dispersing Dirac cones and van Hove singularities. Even though BLG has been extensively studied experimentally, the evidence of this band structure is still elusive, likely due to insufficient energy resolution. Here, we use Landau levels as markers of the energy dispersion and analyze the Landau level spectrum in a regime where the cyclotron orbits of electrons or holes in momentum space are small enough to resolve the distinct mini Dirac cones. We identify the presence of four Dirac cones and map out topological transitions induced by displacement field. By clarifying the low-energy properties of BLG bands, these findings provide a valuable addition to the toolkit for graphene electronics.

Abstract Background Lymphovascular invasion (LVI) is a poor prognostic factor in various malignancies. However, its prognostic effect in remnant gastric cancer (RGC) remains unclear. We examined the correlation between LVI and disease prognosis in patients with T1N0-3 or T2-3N0 RGC in whom adjuvant chemotherapy was not indicated and a treatment strategy was not established. Methods We retrospectively analyzed patients with T1N0-3 and T2-3N0 RGC who underwent curative surgery at the Kyoto Prefectural University of Medicine between 1997 and 2019 and at the Kyoto Chubu Medical Center between 2009 and 2019. Results Fifteen of 38 patients (39.5%) with RGC were positive for LVI. Patients with LVI had a significantly poorer prognosis for both overall survival ([OS]: P = 0.006) and recurrence-free survival ([RFS]: P = 0.001) than those without LVI. Multivariate analyses using the Cox proportional hazards model revealed LVI as an independent prognostic factor affecting OS (P = 0.024; hazard ratio 8.27, 95% confidence interval:1.285–161.6) and RFS (P = 0.013; hazard ratio 8.98, 95% confidence interval:1.513–171.2). Conclusions LVI is a prognostic factor for patients with T1N0-3 or T2-3N0 RGC. Evaluating LVI may be useful for determining treatment strategies for RGC.

Abstract We investigate the vibrational and magnetic properties of thin layers of chromium tribromide (CrBr3) with a thickness ranging from three to twenty layers (3–20 L) revealed by the Raman scattering (RS) technique. Systematic dependence of the RS process efficiency on the energy of the laser excitation is explored for four different excitation energies: 1.96 eV, 2.21 eV, 2.41 eV, and 3.06 eV. Our characterization demonstrates that for 12 L CrBr3, 3.06 eV excitation could be considered resonant with interband electronic transitions due to the enhanced intensity of the Raman-active scattering resonances and the qualitative change in the Raman spectra. Polarization-resolved RS measurements for 12 L CrBr3 and first-principles calculations allow us to identify five observable phonon modes characterized by distinct symmetries, classified as the A $$_\text {g}$$ g and E $$_\text {g}$$ g modes. The evolution of phonon modes with temperature for a 16 L CrBr3 encapsulated in hexagonal boron nitride flakes demonstrates alterations of phonon energies and/or linewidths of resonances indicative of a transition between the paramagnetic and ferromagnetic state at Curie temperature ( $$T_\text {C} \approx 50$$ T C ≈ 50 K). The exploration of the effects of thickness on the phonon energies demonstrated small variations pronounces exclusively for the thinnest layers in the vicinity of 3–5 L. We propose that this observation can be due to the strong localization in the real space of interband electronic excitations, limiting the effects of confinement for resonantly excited Raman modes to atomically thin layers.

Abstract Flat-band systems with strongly correlated electrons can exhibit a variety of phenomena, such as correlated insulating and topological states, unconventional superconductivity, and ferromagnetism. Rhombohedral multilayer graphene has recently emerged as a promising platform for investigating exotic quantum states due to its hosting of topologically protected surface flat bands at low energy, which have a layer-dependent energy dispersion. However, the complex relationship between the surface flat bands and the highly dispersive high-energy bands makes it difficult to study correlated surface states. In this study, we introduce moiré superlattices as a method to isolate the surface flat bands of rhombohedral multilayer graphene. The observed pronounced screening effects in the moiré potential-modulated rhombohedral multilayer graphene indicate that the two surface states are electronically decoupled. The flat bands that are isolated promote correlated surface states in areas that are distant from the charge neutrality points. Notably, we observe tunable layer-polarized ferromagnetism, which is evidenced by a hysteretic anomalous Hall effect. This is achieved by polarizing the surface states with finite displacement fields.