Gate-Tunable Tunneling Resistance in Graphene/Topological Insulator Vertical Junctions

Graphene-based vertical heterostructures, particularly stacks incorporated with other layered materials, are promising for nanoelectronics. The stacking of two model Dirac materials, graphene and topological insulator, can considerably enlarge the family of van der Waals heterostructures. Despite well understanding of the two individual materials, the electron transport properties of a combined vertical heterojunction are still unknown. Here we show the experimental realization of a vertical heterojunction between Bi2Se3 nanoplate and monolayer graphene. At low temperatures, the electron transport through the vertical heterojunction is dominated by the tunneling process, which can be effectively tuned by gate voltage to alter the density of states near the Fermi surface. In the presence of a magnetic field, quantum oscillations are observed due to the quantized Landau levels in both graphene and the two-dimensional surface states of Bi2Se3. Furthermore, we observe an exotic gate-tunable tunneling resistance under high magnetic field, which displays resistance maxima when the underlying graphene becomes a quantum Hall insulator

Polaritonic Huang-Rhys Factor: Basic Concepts and Quantifying Light-Matter Interaction in Medium

Huang-Rhys (HR) factor, a dimensionless factor that characterizes electron-phonon coupling, has been extensively employed to investigate material properties in various fields. In the same spirit, we present a quantity called polaritonic HR factor to quantitatively describe the effects of (i) light-matter coupling induced by permanent dipoles and (ii) dipole self-energy. The former can be viewed as polaritonic displacements, while the latter is associated with the electronic coupling shift. In the framework of macroscopic quantum electrodynamics, the polaritonic HR factor, coupling shift, and modified light-matter coupling strength in an arbitrary dielectric environment can be evaluated without free parameters, whose magnitudes are in good agreement with the previous experimental results. In addition, polaritonic progression developed in our theory indicates that large polaritonic HR factors can result in light-matter decoupling, multipolariton formation, and non-radiative transition. We believe that this study provides a useful perspective to understand and quantify light-matter interaction in medium

Wide-Dynamic-Range Control of Quantum-Electrodynamic Electron Transfer Reactions in the Weak Coupling Regime

Catalyzing reactions effectively by vacuum fluctuations of electromagnetic fields is a significant challenge within the realm of chemistry. Different from most studies based on vibrational strong coupling, we introduce an innovative catalytic mechanism driven by weakly coupled polaritonic fields. Through the amalgamation of macroscopic quantum electrodynamics (QED) principles with Marcus electron transfer (ET) theory, our results reveal that ET reaction rates can be precisely modulated across a wide dynamic range by controlling the size and structure of nanocavities. Comparing to QED-driven radiative ET rates in free space, plasmonic cavities induce substantial rate enhancements spanning from orders of magnitude ranging from 10^3-fold to 10^1-fold. By contrast, Fabry-Perot cavities engender rate suppression spanning from 10^{-2}-fold to 10^{-1}-fold. This work overcomes the necessity of using strong light-matter interactions in QED chemistry, opening up a new era of manipulating QED-based chemical reactions in a wide dynamic range

Slightly Fluorination of Al₂O₃ ALD Coating on Li₁.₂Mn₀.₅₄Coo.₁₃Ni₀.₁₃O₂ Electrodes: Interface Reaction to Create Stable Solid Permeable Interphase Layer

Improving the performance of cathodes by using surface coatings has proven to be an effective method for improving the stability of Li-ion batteries (LIBs), while a high-quality film satisfying all requirements of electrochemical inertia, chemical stability, and lithium ion conductivity has not been found. In this study, a composite film composed of Al2O3 and AlF3 layers was coated on the surface of Li1.2Mn0.54Co0.13Ni0.13O2 (Li-rich NMC) based electrodes by atomic layer deposition (ALD). By varying the ratio of Al2O3 and AlF3, an optimal coating was achieved. The electrochemical characterization results indicated that the coating with 1 cycle of AlF3 ALD on 5 cycles of Al2O3 ALD (1AlF3-5Al2O3) significantly improved the cycling stability and alleviated the voltage attenuation problem of Li-rich NMC based electrodes by suppressing side reactions between the electrolyte and electrode, as well as inhibiting the transformation of layered Li2MnO3 into a spinel-like phase. After 200 cycles of charge-discharge, the discharge capacity retention of LIB half cells based on 1AlF3-5Al2O3 coated Li-rich NMC electrodes kept at 84%, much higher than that of the uncoated Li-rich NMC (the capacity retention less than 20%)