Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We present a perspective on the status of antiferromagnetism in two-dimensional (2D) materials. Various types of spin-compensated orders are discussed and include non-collinear order, spin spirals and altermagnetism. Spin-orbit effects ultimately determine, whether compounds exhibit long range order, Kosterlitz-Thouless physics, or multiferroic properties and we discuss the basic magnetic prototypes that may arise in 2D materials depending on the magnetic anisotropy and ordering vector. A summary of 2D antiferromagnets that have been characterized experimentally is provided - with particular emphasis on magnetic anisotropies and Neel temperatures. We then outline the ingredients needed to describe the magnetic properties using density functional theory. In particular, the systematic determination of magnetic ground states from the generalized Bloch theorem and the magnetic force theorem, which may be used to calculate magnetic excitations from the Heisenberg model with parameters determined from first principles. The methods are exemplified by application to the monolayer helimagnet NiBr$_2$. Finally, we present a summary of predicted and prospective 2D antiferromagnets and discuss the challenges associated with the prediction of Néel temperatures from first principles.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Excitons in twisted bilayers of transition metal dichalcogenides have strongly modified dispersion relations due to the formation of periodic moiré potentials. The strong coupling to a light field in an optical cavity leads to the appearance of moiré polaritons. In this paper, we derive a theoretical model for the linear absorption spectrum of the coupled moiré polariton-phonon system based on the time-convolutionless (TCL) approach. Results obtained by numerically solving the TCL equation are compared to those obtained in the Markovian limit and from a perturbative treatment of non-Markovian corrections. A key quantity for the interpretation of the findings is the generalized phonon spectral density. We discuss the phonon impact on the spectrum for realistic moiré exciton dispersions by varying twist angle and temperature.&amp;#xD;Key features introduced by the coupling to phonons are broadenings and energy shifts of the upper and lower polariton peak and the appearance of phonon sidebands between them. We analyze these features with respect to the role of Markovian and non-Markovian effects and find that they strongly depend on the twist angle. We can distinguish between the regimes of large, small, and intermediate twist angles. In the latter phonon effects are particularly pronounced due to dominating phonon transitions into regions which are characterized by van Hove singularities in the density of states.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In-plane optical properties of two-dimensional bismuth oxychalcogenides Bi2O2X (X = S, Se, and Te) are reported for a wide spectral range of 0.73–6.42 eV and at temperatures of 4.5–500 K by spectroscopic ellipsometry. At room temperature, Bi2O2S, Bi2O2Se, and Bi2O2Te exhibit an indirect band gap of 1.18 ± 0.02, 0.95 ± 0.01, and 0.60 ± 0.01, respectively. As the temperature decreases, the indirect absorption edge of Bi2O2S undergoes a blueshift, while the indirect band gap of Bi2O2Se shows a redshift, and Bi2O2Te remains independent of temperature. The chalcogenide-dependent behavior as a function of temperature may be relevant to electron–phonon interactions in Bi2O2X materials. The observed pseudo-isotropic complex dielectric function and optical absorption coefficient by spectroscopic ellipsometry are directly compared with the first-principles calculations with a hybrid functional approach.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Two-dimensional, 2D, niobium carbide MXene, Nb2CTx, has attracted attention due to its extraordinarily high photothermal conversion efficiency that has applications ranging from medicine, for tumor ablation, to solar energy conversion. Here, we characterize its electronic properties and investigate the ultrafast dynamics of its photoexcitations with a goal of shedding light onto the origins of its unique properties. Through density functional theory, DFT, calculations, we find that Nb2CTx is metallic, with a small but finite density of states at the Fermi level for all experimentally relevant terminations of as-fabricated Nb2CTx. In agreement with this prediction, THz spectroscopy reveals an intrinsic long-range conductivity of ~ 60 Ω-1 cm-1, with significant charge carrier localization and a charge carrier density (~1020 cm-1) comparable to Mo-based MXenes. Excitation with 800 nm pulses results in a rapid enhancement in photoconductivity, which decays to less than 25% of its peak value within several picoseconds, undelying the efficient photothermal conversion. At the same time, a small fraction of photoinjected excess carriers persists for hundreds of picoseconds, and can potentially be utilized in photocatalysis or other energy conversion applications.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We perform extensive density functional theory (DFT) calculations to determine the stability and elementary properties of 4249 previously unexplored monolayer crystals. The monolayers comprise the most stable subset (energy within 0.1 eV/atom of the convex hull) of a larger portfolio of two-dimensional (2D) materials recently discovered using a deep generative model and systematic lattice decoration schemes. The relaxed 2D structures are run through the basic property workflow of the Computational 2D Materials Database (C2DB) to evaluate the dynamical stability and obtain the stiffness tensor, piezoelectric tensor, deformation potentials, Born and Bader charges, electronic band structure, effective masses, plasma frequency, Fermi surface, projected density of states, magnetic moments, magnetic exchange couplings, magnetic anisotropy, topological indices, optical- and infrared polarisability. We provide statistical overviews of the property data and highlight a few specific examples of interesting materials. Our work exposes previously unknown parts of the 2D chemical space and provides a basis for the discovery of 2D materials with specific properties. All data is available in the C2DB.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A comprehensive investigation into the exciton behaviors in indium selenide (InSe) is yet to be conducted. Here, the power factor <jats:italic>K</jats:italic>, which can characterize the excitonic behaviors, was determined for InSe with varying thicknesses. The photoluminescence results suggest that defects play a dominant role in the recombination of excitons with varying thicknesses. Consequently, the free exciton peak at 931 nm, which is linked to the double exciton emission behavior, becomes obscured by the presence of a bound exciton peak at 980 nm resulting from defect-induced recombination. However, at specific thicknesses and power levels, the enhancement of quantum confinement effect coupled with a reduction in defect proportion enables the observation of the peak corresponding to free exciton. Furthermore, the extracted <jats:italic>K</jats:italic> values from the InSe photodetectors corroborated the aforementioned findings. The results presented here provide an in-depth understanding of exciton behavior in InSe and provide theoretical underpinning for the development of InSe-based optoelectronics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A van der Waals heterostructure containing an atomically thin monolayer (ML) transition-metal dichalcogenide as a single-photon emitting layer is emerging as an intriguing solid-state quantum-photonic platform. Here, we report the utilization of spin-coating of silica nanoparticles for semi-deterministically creating the spectrally isolated, energetically stable, and narrow-linewidth single-photon emitters in ML-WS<jats:sub>2</jats:sub>. We also demonstrate that long-duration low-temperature annealing of the photonic heterostructure in the vacuum removes the energetically unstable emitters that are present due to fabrication-associated residue and lead to the emission of single-photons in a <jats:inline-formula> <jats:tex-math/> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>&lt;</mml:mo> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="tdmad4b38ieqn1.gif" xlink:type="simple"/> </jats:inline-formula>25 nm narrowband visible spectral range centered at ~620 nm. This work may pave the way toward realizing a hybrid-quantum-photonic platform containing a van der Waals heterostructure/device and an atomic-vapor system emitting/absorbing in the same visible spectral range.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Deep learning (DL) methodologies have led to significant advancements in various domains, facilitating intricate data analysis and enhancing predictive accuracy and data generation quality through complex algorithms. In materials science, the extensive computational demands associated with high-throughput screening techniques such as density functional theory, coupled with limitations in laboratory production, present substantial challenges for material research. DL techniques are poised to alleviate these challenges by reducing the computational costs of simulating material properties and by generating novel materials with desired attributes. This comprehensive review document explores the current state of DL applications in materials design, with a particular emphasis on two-dimensional materials. The article encompasses an in-depth exploration of data-driven approaches in both forward and inverse design within the realm of materials science.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Two-dimensional (2D) layered materials and heterostructures have garnered significant attention for their exploration of uncharted scientific phenomena and their versatile applications. The customization of van der Waals heterostructures heavily relies on their transfer assembly techniques. While traditional dry or wet transfer methods show promise in manipulating 2D materials and heterostructures, challenges such as residues from supporting layers, incomplete substrate etching, embedded bubbles at interfaces, and transfer-induced damages like cracks and wrinkles still pose significant hurdles. In this review, we comprehensively examine the state of transfer technology, identifying the origins of these technical challenges and discussing potential solutions. We specifically focus on strategies developed within the last 3–5 years that aim to address these complex transfer issues, facilitating the integration of 2D materials and heterostructures into existing silicon-based technologies. Finally, we offer perspectives to guide the optimization of each transfer method and inspire future industrial applications of 2D materials.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The use of nano-Raman spectroscopy to study two-dimensional (2D) systems is presented here. The nano (tip-enhanced) Raman spectroscopy technique is briefly introduced, addressing some new theoretical aspects for Raman spectroscopy in the near-field regime, including field coherence, field distribution and the relevance of atomic description and quenching effects. State-of-the-art results in graphene and transition metal dichalcogenides are presented, exploring the connection between micro- and nano-Raman metrology. Various aspects such as defects, homojunctions, twisted-bilayer structures, localized emissions at bubbles, wrinkles, and borders, as well as substrate and coherence effects are addressed in detail. The paper concludes by outlining the perspectives for nano-Raman spectroscopy in 2D systems, highlighting its potential for advancing our understanding of nanoscale phenomena and facilitating further breakthroughs in materials science and characterization.</jats:p>