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Loss is a critical performance metric in piezoelectric devices, directly impacting energy conversion efficiency and the overall stability of device operation. However, the complexity arises from the fact that losses in piezoelectric vibrators encompass dielectric, mechanical, and piezoelectric components, making their distinction challenging due to the interplay of various losses on admittance and impedance near the resonant frequency. In this paper, a model employing a mechanically unbounded, electrically open circuit longitudinal piezoelectric oscillator is utilized. We derived impedance and phase expressions for the piezoelectric oscillator, accounting for different types of losses, based on the third order of the piezoelectric equation. Subsequently, we conduct a numerical analysis of the theoretically derived expressions, investigating the impact of the three distinct loss types on impedance and phase values. Our study aims to establish a quantitative relationship between dielectric, mechanical, and piezoelectric losses and the phase characteristic data. The results offer valuable insights into the measurement of diverse losses in piezoelectric vibrators, presenting a methodological advancement in this field. [ABSTRACT FROM AUTHOR]

Quantum phase transition refers to the abrupt change of ground states of many-body systems driven by quantum fluctuations. It hosts various intriguing exotic states around its quantum critical points approaching zero temperature. Here we report the spectroscopic and transport evidences of quantum critical phenomena of an exciton Mott metal-insulator-transition in black phosphorus. Continuously tuning the interplay of electron-hole pairs by photo-excitation and using Fourier-transform photo-current spectroscopy as a probe, we measure a comprehensive phase diagram of electron-hole states in temperature and electron-hole pair density parameter space. We characterize an evolution from optical insulator with sharp excitonic transition to metallic electron-hole plasma phases featured by broad absorption and population inversion. We also observe strange metal behavior that resistivity is linear in temperature near the Mott transition boundaries. Our results exemplify an ideal platform to investigating strongly-correlated physics in semiconductors, such as crossover between superconductivity and superfluity of exciton condensation. The exciton Mott transition refers to a transition from an insulating state of gas-like excitons to strongly correlated electron-hole plasma phases in photoexcited semiconductors. Here the authors experimentally study such a transition in black phosphorus and reveal its quantum critical properties. [ABSTRACT FROM AUTHOR]

Moiré superlattices have led to observations of exotic emergent electronic properties such as superconductivity and strong correlated states in small-rotation-angle twisted bilayer graphene (tBLG)1,2. Recently, these findings have inspired the search for new properties in moiré plasmons. Although plasmon propagation in the tBLG basal plane has been studied by near-field nano-imaging techniques3–7, the general electromagnetic character and properties of these plasmons remain elusive. Here we report the direct observation of two new plasmon modes in macroscopic tBLG with a highly ordered moiré superlattice. Using spiral structured nanoribbons of tBLG, we identify signatures of chiral plasmons that arise owing to the uncompensated Berry flux of the electron gas under optical pumping. The salient features of these chiral plasmons are shown through their dependence on optical pumping intensity and electron fillings, in conjunction with distinct resonance splitting and Faraday rotation coinciding with the spectral window of maximal Berry flux. Moreover, we also identify a slow plasmonic mode around 0.4 electronvolts, which stems from the interband transitions between the nested subbands in lattice-relaxed AB-stacked domains. This mode may open up opportunities for strong light–matter interactions within the highly sought after mid-wave infrared spectral window8. Our results unveil the new electromagnetic dynamics of small-angle tBLG and exemplify it as a unique quantum optical platform.Two new plasmon modes are observed in macroscopic twisted bilayer graphene with a highly ordered moiré superlattice, the first being the signature of chiral plasmons and the second a slow plasmonic mode around 0.4 electronvolts. [ABSTRACT FROM AUTHOR]

Background: Histone demethylase UTX has been reported to participate in the occurrence and development of many cancers in tissue-specific manners. However, the role of UTX in non-small cell lung cancer (NSCLC) and exactly what regulates the expression of UTX remains unclear. Here, we analyzed the role of UTX in NSCLC in association with the widely recognized tumor driver epidermal growth factor receptor (EGFR). Methods: UTX levels in clinical samples were detected by immunohistochemistry staining, western blotting and real-time quantitative PCR. The expression of UTX in tumor tissue was correlated with the phosphorylation of EGFR. Cell proliferation and migration were evaluated by MTT and wound-healing assays. The impact of EGFR and its downstream pathways on UTX was explored with corresponding inhibitors, and examined by western blotting and real-time quantitative PCR. Results: In this study, we found that the expression of UTX in cancer tissues of patients with NSCLC was significantly higher than that in paracancerous tissues, and positively associated with EGFR phosphorylation levels. In addition, in NSCLC cell lines, UTX can promote proliferation and migration, while inhibition of its enzyme activity suppressed cell growth. Moreover, UTX expression was significantly upregulated when EGFR signaling pathway was activated, and vice versa when EGFR pathway was inhibited by tyrosine kinase inhibitor. Further mechanistic studies suggested that the activation of EGFR activated its downstream JAK/STAT3 signaling pathway and promoted STAT3 phosphorylation; the phosphorylated STAT3 transcriptionally promoted the levels of UTX. Conclusions: These results suggest an "EGFR-STAT3-UTX" axis that plays an oncogenic role in NSCLC. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials are promising for next-generation photo detection because of their exceptional properties such as a strong interaction with light, electronic and optical properties that depend on the number of layers, and the ability to form hybrid structures. However, the intrinsic detection ability of 2D material-based photodetectors is low due to their atomic thickness. Photogating is widely used to improve the responsivity of devices, which usually generates large noise current, resulting in limited detectivity. Here, we report a molybdenum-based phototransistor with MoS2 channel and α-MoO3-x contact electrodes. The device works in a photo-induced barrier-lowering (PIBL) mechanism and its double heterojunctions between the channel and the electrodes can provide positive feedback to each other. As a result, a detectivity of 9.8 × 1016 cm Hz1/2 W−1 has been achieved. The proposed double heterojunction PIBL mechanism adds to the techniques available for the fabrication of 2D material-based phototransistors with an ultrahigh photosensitivity. Here, the authors exploit a photo-induced barrier-lowering mechanism in MoS2/ α-MoO3-x heterojunctions to realize two-dimensional phototransistors with enhanced performance and fast response at low bias voltage. [ABSTRACT FROM AUTHOR]

Ferroelectric field effect transistor (FeFET) emerges as an intriguing non-volatile memory technology due to its promising operating speed and endurance. However, flipping the polarization requires a high voltage compared with that of reading, impinging the power consumption of writing a cell. Here, we report a CMOS compatible FeFET cell with low operating voltage. We engineer the ferroelectric Hf1-xZrxO2 (HZO) thin film to form negative capacitance (NC) gate dielectrics, which generates a counterclock hysteresis loop of polarization domain in the few-layered molybdenum disulfide (MoS2) FeFET. The unstabilized negative capacitor inherently supports subthermionic swing rate and thus enables switching the ferroelectric polarization with the hysteresis window much less than half of the operating voltage. The FeFET shows a high on/off current ratio of more than 107 and a counterclockwise memory window (MW) of 0.1 V at a miminum program (P)/erase (E) voltage of 3 V. Robust endurance (103 cycles) and retention (104 s) properties are also demonstrated. Our results demonstrate that the HZO/MoS2 ferroelectric memory transistor can achieve new opportunities in size- and voltage-scalable non-volatile memory applications. [ABSTRACT FROM AUTHOR]

In this work, we study the interlayer phonon vibration modes, the layer-numberdependent optical bandgap, and the anisotropic photoluminescence (PL) spectra of atomically thin rhenium diselenide (ReSe) for the first time. The ultralow frequency interlayer Raman spectra and the polarization-resolved high frequency Raman spectra in ReSe allow the identification of its layer number and crystal orientation. Furthermore, PL measurements show the anisotropic optical emission intensity of the material with its bandgap increasing from 1.26 eV in the bulk to 1.32 eV in the monolayer. The study of the layer-number dependence of the Raman modes and the PL spectra reveals relatively weak van der Waal's interaction and two-dimensional (2D) quantum confinement in the atomically thin ReSe. The experimental observation of the intriguing anisotropic interlayer interaction and tunable optical transition in monolayer and multilayer ReSe establishes the foundation for further exploration of this material in the development of anisotropic optoelectronic devices functioning in the near-infrared spectrum, which is important for many applications in optical communication and infrared sensing. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Semi-metallic graphene and semiconducting monolayer transition-metal dichalcogenides are the most intensively studied two-dimensional materials of recent years. Lately, black phosphorus has emerged as a promising new two-dimensional material due to its widely tunable and direct bandgap, high carrier mobility and remarkable in-plane anisotropic electrical, optical and phonon properties. However, current progress is primarily limited to its thin-film form. Here, we reveal highly anisotropic and strongly bound excitons in monolayer black phosphorus using polarization-resolved photoluminescence measurements at room temperature. We show that, regardless of the excitation laser polarization, the emitted light from the monolayer is linearly polarized along the light effective mass direction and centres around 1.3 eV, a clear signature of emission from highly anisotropic bright excitons. Moreover, photoluminescence excitation spectroscopy suggests a quasiparticle bandgap of 2.2 eV, from which we estimate an exciton binding energy of ∼0.9 eV, consistent with theoretical results based on first principles. The experimental observation of highly anisotropic, bright excitons with large binding energy not only opens avenues for the future explorations of many-electron physics in this unusual two-dimensional material, but also suggests its promising future in optoelectronic devices. [ABSTRACT FROM AUTHOR]

Graphene-based photonic devices, such as ultrafast photodetectors, optical modulators and tunable surface plasmon polariton devices, have experienced rapid development in recent years because they benefit greatly from graphene's strong field-controlled optical response. Here, we demonstrate a graphene/silicon-heterostructure photodiode formed by integrating graphene onto a silicon optical waveguide on a silicon-on-insulator (SOI) with a near to mid-infrared operational range. The waveguide enables absorption of evanescent light that propagates parallel to the graphene sheet, which results in a responsivity as high as 0.13 A W−1 at a 1.5 V bias for 2.75 µm light at room temperature. A photocurrent dependence on bias polarity was observed and attributed to two distinct mechanisms for optical absorption, that is, direct and indirect transitions in graphene at 1.55 µm and 2.75 µm, respectively. Our result demonstrates the use of in-plane absorption in a graphene-monolayer structure and the feasibility of exploiting indirect transitions in graphene/silicon-heterostructure waveguides for mid-infrared detection. [ABSTRACT FROM AUTHOR]

Heterostructures based on two-dimensional (2D) materials have sparked wide interests in both fundamental physics and applied devices. Recently, Dirac/Weyl semimetals are emerging as capable functional materials for optoelectronic devices. However, thus far the interfacial coupling of an all-semimetal 2D heterostructure has not been investigated, and its effects on optoelectronic properties remain less well understood. Here, a heterostructure comprising of all semi-metallic constituents, namely graphene and WTe2, is fabricated. Standard photocurrent measurements on a graphene/WTe2 phototransistor reveal a pronounced photocurrent enhancement (a photoresponsivity ~8.7 A/W under 650 nm laser illumination). Transport and photocurrent mapping suggest that both photovoltaic and photothermoelectric effects contribute to the enhanced photoresponse of the hybrid system. Our results help to enrich the understanding of new and emerging device concepts based on 2D layered materials. [ABSTRACT FROM AUTHOR]

The article discusses the study conducted by Konstantin Novoselov and colleagues, published at the journal "Nature Materials," which focuses on the type of light-emitting diode (LED) based on heterostructures. Explored are three types of 2D layered materials including metallic graphene, insulating hexagonal boron nitride (hBN) and semiconducting monolayer transition metal dichalcogenides (TMDCs). The tunable electronic bandgap in 2D material is evaluated.

Recently rediscovered black phosphorus is a layered semiconductor with promising electronic and photonic properties. Dynamic control of its bandgap can allow for the exploration of new physical phenomena. However, theoretical investigations and photoemission spectroscopy experiments indicate that in its few-layer form, an exceedingly large electric field in the order of several volts per nanometre is required to effectively tune its bandgap, making the direct electrical control unfeasible. Here we reveal the unique thickness-dependent bandgap tuning properties in intrinsic black phosphorus, arising from the strong interlayer electronic-state coupling. Furthermore, leveraging a 10 nm-thick black phosphorus, we continuously tune its bandgap from ∼300 to below 50 meV, using a moderate displacement field up to 1.1 V nm−1. Such dynamic tuning of bandgap may not only extend the operational wavelength range of tunable black phosphorus photonic devices, but also pave the way for the investigation of electrically tunable topological insulators and semimetals. [ABSTRACT FROM AUTHOR]

Heterostructures based on two-dimensional (2D) materials have sparked wide interests in both fundamental physics and applied devices. Recently, Dirac/Weyl semimetals are emerging as capable functional materials for optoelectronic devices. However, thus far the interfacial coupling of an all-semimetal 2D heterostructure has not been investigated, and its effects on optoelectronic properties remain less well understood. Here, a heterostructure comprising of all semi-metallic constituents, namely graphene and WTe2, is fabricated. Standard photocurrent measurements on a graphene/WTe2 phototransistor reveal a pronounced photocurrent enhancement (a photoresponsivity ~8.7 A/W under 650 nm laser illumination). Transport and photocurrent mapping suggest that both photovoltaic and photothermoelectric effects contribute to the enhanced photoresponse of the hybrid system. Our results help to enrich the understanding of new and emerging device concepts based on 2D layered materials. [ABSTRACT FROM AUTHOR]