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<jats:title>Abstract</jats:title> <jats:p>Two-dimensional (2D) metals can host gapless plasmonic excitations that strongly couple to electrons and thus may significantly affect superconductivity. To investigate the dynamical interplay of the electron-electron and electron-phonon interactions in the theory of 2D superconductivity, we apply a full momentum- and frequency-dependent one-loop theory treating electron-phonon, electron-plasmon, and phonon-plasmon coupling with the same accuracy. We tune the strength of the Coulomb interaction by varying the external screening $\varepsilon_{ext}$ to the layered superconductor and find three distinct regions. At weak screening, superconductivity is mediated by plasmons. In the opposite limit conventional electron-phonon interactions dominate. In between, we find a suppressed superconducting state. Our results show that even in conventional electron-phonon coupled layered materials, superconductivity can be significantly enhanced by the electron-plasmon coupling in a manner that can be controlled by the external screening.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Hexagonal boron nitride (hBN) has emerged as a promising two-dimensional (2D) material for many applications in electronics and photonics. Although its linear and nonlinear optical properties have been extensively studied, the interaction of hBN with high-intensity laser pulses, which is important for realizing high-harmonic generation, creating deterministic defects as quantum emitters, and resist-free patterning in this material, has not been investigated. Here we report the first systematic study of dielectric breakdown in CVD-grown hBN monolayers induced by single femtosecond laser pulses. We report a breakdown fluence of 0.7 J/cm2, which is at least&amp;#xD;7× higher than that of other monolayer 2D materials. A clean removal of hBN without leaving traces behind or causing lateral damage is demonstrated. The ablation features exhibit excellent fidelity with very small edge roughness, which we attribute to its ultrahigh fracture toughness due to its heterogeneous nature with 3-fold symmetry. Moreover, even though defects are known to&amp;#xD;be abundant in CVD-grown hBN, we show experimentally and theoretically that its nonlinear optical breakdown is nearly intrinsic as defects only marginally lower the breakdown threshold. On top of this, we observe that hBN monolayers have a 4-5× lower breakdown threshold than&amp;#xD;their bulk equivalent. The last two observations can be understood if the carrier generation in monolayers is intrinsically enhanced due to its 2D nature. Finally, we demonstrate laser patterning of array of holes and lines in hBN with sub-wavelength feature sizes. Our work advances the fundamental knowledge of light-hBN interaction in the strong field regime and firmly establishes femtosecond lasers as novel and promising tools for resist-free patterning of hBN monolayers with high fidelity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Niobium chloride (Nb3Cl8) is a layered 2D semiconducting material with many exotic properties including a breathing kagome lattice, a topological flat band in its band structure, and a crystal structure that undergoes a structural and magnetic phase transition at temperatures below 90 K. Despite being a remarkable material with fascinating new physics, the understanding of its phonon properties is at its infancy. In this study, we investigate the phonon dynamics of Nb3Cl8 in bulk and few layer flakes using polarized Raman spectroscopy and density-functional theory (DFT) analysis to determine the material’s vibrational modes, as well as their symmetrical representations and atomic displacements. We experimentally resolved 12 phonon modes, 5 of which are A1g modes while the remaining 7 are Eg modes, which is in strong agreement with our DFT calculation. Layer-dependent results suggest that the Raman peak positions are mostly insensitive to changes in layer thickness, while peak intensity and FWHM are affected. Raman measurements as a function of excitation wavelength (473 – 785 nm) show a significant increase of the peak intensities when using a 473 nm excitation source, suggesting a near resonant condition. Temperature-dependent Raman experiments carried out above and below the transition temperature did not show any change in the symmetries of the phonon modes, suggesting that the structural phase transition is likely from the high temperature P3̅m1 phase to the low-temperature R3̅m phase. Magneto-Raman measurements carried out at 140 and 2 K between -2 to 2 T show that the Raman modes are not magnetically coupled. Overall, our study presented here significantly advances the fundamental understanding of layered Nb3Cl8 material which can be further exploited for future applications.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In recent years, much research has been undertaken to investigate the suitability of two-dimensional materials to act as single-photon sources with high optical and quantum optical quality. Amongst them, transition-metal dichalcogenides, especially WSe<jats:sub>2</jats:sub>, have been one of the subjects of intensive studies. Yet, their single-photon purity and photon indistinguishability, remain the most significant challenges to compete with mature semiconducting systems such as self-assembled InGaAs quantum dots. In this work, we explore the emission properties of quantum emitters in a WSe<jats:sub>2</jats:sub> monolayer which are induced by metallic nanoparticles. Under quasi-resonant pulsed excitation, we verify clean single-photon emission with a g<jats:sup>(2)</jats:sup>(0) = 0.036 ± 0.004. Furthermore, we determine its temperature dependent coherence time via Michelson interferometry, where a value of (13.5 ± 1.0) ps is extracted for the zero-phonon line (ZPL) at 4 K, which reduces to (9 ± 2) ps at 8 K. Associated time-resolved photoluminescence experiments reveal a decrease of the decay time from (2.4 ± 0.1) ns to (0.42 ± 0.05) ns. This change in decay time is explained by a model which considers a Förster-type resonant energy transfer process which yields a strong temperature induced energy loss from the SPE to the nearby Ag nanoparticle.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The family of 2D ferromagnets is in the center of research for novel spintronics applications. Among the various 2D ferromagnets, Fe3GeTe2 has drawn significant attention since it combines a high Curie temperature with a van der Waals structure, which allows easy exfoliation, and a high spin polarization/large spin-orbit coupling. The presence of interfacial DMI in 2D ferromagnets have a significant impact on the behavior of magnetic domain walls, which are fundamental in magnetic memory and logic devices. By controlling the interfacial DMI, it is possible to manipulate the motion of domain walls and the magnetic domain configuration, which is essential for the development of efficient and reliable magnetic devices. In this study, we investigate the effect of an, inversion symmetry breaking, oxidized layer on the magnetic domain structure of Fe3GeTe2 flakes due to the emergence of interfacial DMI. By combining Magneto Optical Kerr Effect microscopy images (MOKE) and micromagnetic simulations, we study the formation of a circular double wall domain lattice in oxidized flakes under specific field cooling and magnetic field sweeping protocols. Their formation is attributed to a competition between the exchange interaction both symmetric and antisymmetric (associated to interfacial DMI), magnetocrystalline anisotropy and the external magnetic field. The circular double wall domains have a diameter of several microns, a magnetic structure resembling that of a skyrmionium and are arranged in regular lattice that survives thermal fluctuations close to Tc. Our results suggest that these circular double wall domains transition to Néel type skyrmions after a magnetic field threshold. These findings could have important implications for the design and optimization of 2D ferromagnetic materials for spintronic applications.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study effects of strain on the electronic properties of the kagome lattice in a tight-binding formalism with spin-orbit coupling (SOC). The degeneracy&amp;#xD;at the Γ point evolves into a pair of emergent tilted Dirac cones under uniaxial strain, where the anisotropy and tilting of the bands depend on the magnitude and direction of the strain field. SOC opens gaps at the emergent Dirac points, making the flatband topological, characterized by a nontrivial Z<jats:sub>2</jats:sub> index. Strains of a few percent drive the system into trivial or topological phases. This confirms that moderate strain can be used to engineer anisotropic Dirac bands with tunable properties to study new phases in kagome lattices.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Multifunctional flexible polymer composites have proliferated in different industries. MXenes, as the rising star of 2D materials, offer unique combinations of properties including metallic conductivity, hydrophilicity, high specific capacitance, and solution processability, as well as mechanical flexibility and robustness that accentuate them for the fabrication of multifunctional composites. 2D flake structure and abundant surface terminations of MXene facilitate its integration into polymer matrices to develop high-performance composites. Polyimides (PIs) are high-temperature engineering polymers that have rendered their way into aerospace and electronics industries due to their outstanding mechanical strength, high chemical resistance, high thermal stability, excellent electrical and thermal insulation properties. Amalgamating the outstanding characteristics of these two materials, this paper is the first review to summarize advancements in PI/MXene nanocomposites to address the methods of preparation and the effect of MXene loading on the target application e.g. energy conversion and storage, electromagnetic interference shielding, sensing, and fire-retardancy. The review commences with a critical discussion on PI/MXene nanocomposite fabrication methods. Next, a comprehensive review of the properties and applications of PI/MXene nanocomposites is provided. Lastly, based on the current developments of PI/MXene nanocomposites, this paper is concluded with the prominent characteristics of PI/MXene composites regarding the target application and identifying the gaps and challenges to develop multifunctional composites.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Photo-excited electrons and holes in insulators, above a critical density and below a critical temperature, can condense to form an electron–hole liquid (EHL) phase. However, observing the EHL phase at room temperature is extremely challenging. Here, we introduce the monolayer <jats:inline-formula> <jats:tex-math><?CDATA $\mathrm{MoSi}_{2}{\mathrm{Z}}_{4}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">M</mml:mi> <mml:mi mathvariant="normal">o</mml:mi> <mml:mi mathvariant="normal">S</mml:mi> <mml:mi mathvariant="normal">i</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Z</mml:mi> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="tdmace83bieqn1.gif" xlink:type="simple" /> </jats:inline-formula> (Z = N, As, P) series of compounds as a promising platform for observing the EHL phase at room temperature. The higher impact of the Coulomb interactions in two dimensions helps these monolayers support the EHL phase with an increased EHL binding energy and transition temperature, along with strongly bound excitons. Our findings motivate further exploration of the <jats:inline-formula> <jats:tex-math><?CDATA $\mathrm{MoSi}_{2}{\mathrm{Z}}_{4}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">M</mml:mi> <mml:mi mathvariant="normal">o</mml:mi> <mml:mi mathvariant="normal">S</mml:mi> <mml:mi mathvariant="normal">i</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Z</mml:mi> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="tdmace83bieqn2.gif" xlink:type="simple" /> </jats:inline-formula> monolayers for realizing the EHL phase at high temperatures to harness collective phenomena for optoelectronic applications.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Modulation of the Fermi level using an ultraviolet (UV)-assisted photochemical method is demonstrated in tungsten diselenide monolayers. Systematic shifts and relative intensities between charged and neutral exciton species indicate a progressive and controllable decrease of the electron density and switch tungsten diselenide from n-type to a p-type semiconductor. The presence of chlorine in the 2D crystal shifts the Fermi level closer to the valence band while the effect can be only partially reversible via continuous wave laser rastering process. Chlorine species in the lattice are validated by x-ray photoelectron spectroscopy, while density functional theory calculations predict that adsorption of chlorine on the selenium vacancy sites leads to p-type doping. The results of our study indicate that photochemical techniques have the potential to enhance the performance of various 2D materials, making them suitable for integrated optoelectronics such as lateral nanopatterned p–n junctions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Structure engineering of hybrid materials has been proved to be an efficient method to screen out superior photocatalysis. The distribution and bonding environment of covalent linkage segments can be well regulated through structure decoration. Here, we propose a controlled strategy to optimize the photocatalytic performance of hybrid catalysts. Systematic adjusting of the performance can be achieved by introducing organic components into the carbon supporter. Under the guidance of this strategy, fluoride graphdiyne (FGDY) and phloroglucinol regulating FGDY (P-FGDY) is compounded with titanium dioxide (TiO<jats:sub>2</jats:sub>) under solvent thermal condition to obtain hybrid catalyst FGDY/TiO<jats:sub>2</jats:sub> and P-FGDY/TiO<jats:sub>2</jats:sub>, respectively. Notably, the as-prepared P-FGDY/TiO<jats:sub>2</jats:sub> exhibits superior enhancements towards photocatalytic degradation of rhodamine B, methylene blue, and levofloxacin under visible-light irradiation compared with FGDY/TiO<jats:sub>2</jats:sub>. These enhanced photocatalytic activities stem from the fact that the regulation of FGDY could further increase the photogenerated electron and hole separation efficiency of hybrid catalyst. This work provides a novel regulating pathway to optimize the photocatalytic activity of carbon-based hybrid photocatalysis material systems.</jats:p>