Showing papers on "Electronic structure published in 2022"

Identification of Fenton-like active Cu sites by heteroatom modulation of electronic density

Abstract: Significance The Fenton-like process based on peroxymonosulfate (PMS) has been widely investigated and recognized as a promising alternative in recent years for the degradation of persistent organic pollutants. However, the sluggish kinetics of PMS activation results in prohibitive costs and substantial chemical inputs, impeding its practical applications in water purification. This work demonstrates that tuning the electronic structure of single-atom sites at the atomic level is a powerful approach to achieve superior PMS activation kinetics. The Cu-based catalyst with the optimized electronic structure exhibits superior performance over most of the state-of-the-art heterogeneous Fenton-like catalysts, while homogeneous Cu(II) shows very poor activity. This work provides insights into the electronic structure regulation of metal centers and structure–activity relationship at the atomic level. Developing heterogeneous catalysts with atomically dispersed active sites is vital to boost peroxymonosulfate (PMS) activation for Fenton-like activity, but how to controllably adjust the electronic configuration of metal centers to further improve the activation kinetics still remains a great challenge. Herein, we report a systematic investigation into heteroatom-doped engineering for tuning the electronic structure of Cu-N4 sites by integrating electron-deficient boron (B) or electron-rich phosphorus (P) heteroatoms into carbon substrate for PMS activation. The electron-depleted Cu-N4/C-B is found to exhibit the most active oxidation capacity among the prepared Cu-N4 single-atom catalysts, which is at the top rankings of the Cu-based catalysts and is superior to most of the state-of-the-art heterogeneous Fenton-like catalysts. Conversely, the electron-enriched Cu-N4/C-P induces a decrease in PMS activation. Both experimental results and theoretical simulations unravel that the long-range interaction with B atoms decreases the electronic density of Cu active sites and down-shifts the d-band center, and thereby optimizes the adsorption energy for PMS activation. This study provides an approach to finely control the electronic structure of Cu-N4 sites at the atomic level and is expected to guide the design of smart Fenton-like catalysts.

Interface Engineering of Co(OH)2 Nanosheets Growing on the KNbO3 Perovskite Based on Electronic Structure Modulation for Enhanced Peroxymonosulfate Activation.

Abstract: Material-enhanced heterogonous peroxymonosulfate (PMS) activation on emerging organic pollutant degradation has attracted intensive attention, and a challenge is the electron transfer efficiency from material to PMS for radical production. Herein, an interface architecture of Co(OH)2 nanosheets growing on the KNbO3 perovskite [Co(OH)2/KNbO3] was developed, which showed high catalytic activity in PMS activation. A high reaction rate constant (k1) of 0.631 min-1 and complete removal of pazufloxacin within 5 min were achieved. X-ray photoelectron spectroscopy, X-ray absorption near edge structure spectra, and density functional theory (DFT) calculations revealed the successful construction of the material interface and modulated electronic structure for Co(OH)2/KNbO3, resulting in the hole accumulation on Co(OH)2 and electron accumulation on KNbO3. Bader topological analysis on charge density distribution further indicates that the occupations of Co-3d and O-2p orbitals in Co(OH)2/KNbO3 are pushed above the Fermi level to form antibonding states (σ*), leading to high chemisorption affinity to PMS. In addition, more reactive Co(II) with the closer d-band center to the Fermi level results in higher electron transfer efficiency and lower decomposition energy of PMS to SO4•-. Moreover, the reactive sites of pazufloxacin for SO4•- attack were precisely identified based on DFT calculation on the Fukui index. The pazufloxacin pathways proceeded as decarboxylation, nitroheterocyclic ring opening reaction, defluorination, and hydroxylation. This work can provide a potential route in developing advanced catalysts based on manipulation of the interface and electronic structure for enhanced Fenton-like reaction such as PMS activation.

Electronic interaction between transition metal single-atoms and anatase TiO₂ boosts CO₂ photoreduction with H₂O

Abstract: In the current work, we demonstrate that single Cu atoms, which are site-specifically stabilized in Ti vacancy of TiO 2 , interact with surrounding TiO 2 and control the overall electronic properties (reducibility and defect formation) of TiO 2 .

Noble-Metal High-Entropy-Alloy Nanoparticles: Atomic-Level Insight into the Electronic Structure.

Abstract: The compositional space of high-entropy-alloy nanoparticles (HEA NPs) significantly expands the diversity of the materials library. Every atom in HEA NPs has a different elemental coordination environment, which requires knowledge of the local electronic structure at an atomic level. However, such structure has not been disclosed experimentally or theoretically. We synthesized HEA NPs composed of all eight noble-metal-group elements (NM-HEA) for the first time. Their electronic structure was revealed by hard X-ray photoelectron spectroscopy and density function theory calculations with NP models. The NM-HEA NPs have a lower degeneracy in energy level compared with the monometallic NPs, which is a common feature of HEA NPs. The local density of states (LDOS) of every surface atom was first revealed. Some atoms of the same constituent element in HEA NPs have different LDOS profiles, whereas atoms of other elements have similar LDOS profiles. In other words, one atom in HEA loses its elemental identity and it may be possible to create an ideal LDOS by adjusting the neighboring atoms. The tendency of the electronic structure change was shown by supervised learning. The NM-HEA NPs showed 10.8-times higher intrinsic activity for hydrogen evolution reaction than commercial Pt/C, which is one of the best catalysts.

First-principles investigation of structural stability, electronic and optical properties of suboxide (Zr3O)

Abstract: Zirconium oxides (Zr-O) has been widely used in energy storage system, catalyst, microelectronic, optoelectronics, and high-temperature ceramics etc. Unfortunately, the ground state structure, electronic and optical properties of Zr3O are unclear until now. Here, we apply the first-principles calculations to study the structure, electronic and optical properties of Zr3O. Three Zr3O oxides: rhombohedral (R32), rhombohedral (R-3c) and hexagonal (P6322) phase are studied. The results show that three Zr3O oxides are thermodynamic and dynamical stabilities. The calculated phonon density of state (PhDOS) further demonstrates the stable of Zr3O oxides. In particular, it is found that the rhombohedral (R-3c) Zr3O is slightly more stable than the other two Zr3O oxides. Unlike ZrO2, the Zr3O oxides exhibit better electronic properties due to the electronic jump between Zr- excitation band and Zr- conduction band near the Fermi level. Compared to the hexagonal Zr3O, the host peak of the rhombohedral Zr3O move into the low energy region, which leads to the red shift phenomenon occurs. In addition, it is found that the rhombohedral (R32, No.155) Zr3O oxide has better storage optical properties compared to the other two Zr3O oxides.

Rich nature of Van Hove singularities in Kagome superconductor CsV3Sb5

Abstract: The recently discovered layered kagome metals AV3Sb5 (A = K, Rb, Cs) exhibit diverse correlated phenomena, which are intertwined with a topological electronic structure with multiple van Hove singularities (VHSs) in the vicinity of the Fermi level. As the VHSs with their large density of states enhance correlation effects, it is of crucial importance to determine their nature and properties. Here, we combine polarization-dependent angle-resolved photoemission spectroscopy with density functional theory to directly reveal the sublattice properties of 3d-orbital VHSs in CsV3Sb5. Four VHSs are identified around the M point and three of them are close to the Fermi level, with two having sublattice-pure and one sublattice-mixed nature. Remarkably, the VHS just below the Fermi level displays an extremely flat dispersion along MK, establishing the experimental discovery of higher-order VHS. The characteristic intensity modulation of Dirac cones around K further demonstrates the sublattice interference embedded in the kagome Fermiology. The crucial insights into the electronic structure, revealed by our work, provide a solid starting point for the understanding of the intriguing correlation phenomena in the kagome metals AV3Sb5.

Charge order landscape and competition with superconductivity in kagome metals

Abstract: In the kagome metals AV3Sb5 (A = K, Rb, Cs), three-dimensional charge order is the primary instability that sets the stage for other collective orders to emerge, including unidirectional stripe order, orbital flux order, electronic nematicity and superconductivity. Here, we use high-resolution angle-resolved photoemission spectroscopy to determine the microscopic structure of three-dimensional charge order in AV3Sb5 and its interplay with superconductivity. Our approach is based on identifying an unusual splitting of kagome bands induced by three-dimensional charge order, which provides a sensitive way to refine the spatial charge patterns in neighbouring kagome planes. We found a marked dependence of the three-dimensional charge order structure on composition and doping. The observed difference between CsV3Sb5 and the other compounds potentially underpins the double-dome superconductivity in CsV3(Sb,Sn)5 and the suppression of Tc in KV3Sb5 and RbV3Sb5. Our results provide fresh insights into the rich phase diagram of AV3Sb5. The authors use high-resolution angle-resolved photoemission spectroscopy to determine the microscopic structure of three-dimensional charge order in AV3Sb5 (A = K, Rb, Cs) and its interplay with superconductivity.

Engineering the Local Coordination Environment and Density of FeN4 Sites by Mn Cooperation for Electrocatalytic Oxygen Reduction.

Abstract: Single atom sites (SAS) of FeN4 are clarified as one of the most active components for the oxygen reduction reaction (ORR). Effective strategies by engineering the local coordination environment and site density of FeN4 sites are crucial to further enhance the electrocatalytic ORR performance. Herein, the integration of a second metal of Mn with Fe to construct Fe&Mn/N-C catalysts with enhanced density of FeN4 active sites and modulated electronic structure is reported. The formation of MnN4 centers modulates the local environment of FeN4 sites and reserves more FeN4 embedded in carbon substrate by forming the possible FeN4 -O-MnN4 configurations. Density functional theory calculations demonstrate that the overall energy barrier of ORR is decreased over the FeN4 -O-MnN4 moieties. Therefore, the Fe&Mn/N-C catalyst exhibits enhanced ORR performance both in alkaline and acidic solution (half-wave potentials are 0.904 and 0.781 V). This work provides an effective strategy by modulating the local electronic structure and density of FeN4 active sites to improve the ORR activity and stability through Mn cooperation.

Reliably assessing the electronic structure of cytochrome P450 on today’s classical computers and tomorrow’s quantum computers

Abstract: Significance Chemical simulation is one of the most promising applications for future quantum computers. It is thought that quantum computers may enable accurate simulation for complex molecules that are otherwise impossible to simulate classically; that is, it displays quantum advantage. To better understand quantum advantage in chemical simulation, we explore what quantum and classical resources are required to simulate a series of pharmaceutically relevant molecules. Using classical methods, we show that reliable classical simulation of these molecules requires significant resources and therefore is a promising candidate for quantum simulation. We estimate the quantum resources, both in overall simulation time and the size. The insights from this study pave the way for future quantum simulation of complex molecules.

Band Engineering Induced Conducting 2H‐Phase MoS2 by PdSRe Sites Modification for Hydrogen Evolution Reaction

Abstract: The electronic band structure of MoS2 exerts far‐ranging effects on the applications of these materials, ranging from chemical catalysis, electronic, and magnetic behaviors. However, the underlying relationship between the electronic band structure and activity is largely unknown in heterogeneous catalysis including the hydrogen evolution reaction, partly due to the lack of a controllable methodology to achieve desirable electronic band structures in the 2H‐phase MoS2. Herein it is demonstrated that dual dopants can engineer the band structure of MoS2 by substituting into the adjacent Mo sites. Specifically, these constructed PdRe dimers bridged by sulfur (PdSRe sites) introduce conducting electronic states around the Fermi level to increase the metallic characteristics of MoS2, resulting in metallic‐like behavior, which is initially semiconducting. Furthermore, the efficacy of inducing a phase conversion from 2H to metallic 1T is higher for codoping with dual dopants as compared to that for the use of a single dopant, thereby generating more intrinsically active PdS*Mo sites to further increase active sites density. Ultimately, this leads to the MoS2 catalyst showing a low overpotential of 46 mV at a current density of 10 mA cm−2 and a high exchange current density of 1.524 mA cm−2, along with superior operating durability.

Mo doping and Se vacancy engineering for boosting electrocatalytic water oxidation by regulating the electronic structure of self-supported Co9Se8@NiSe.

Abstract: Oxygen evolution reactions (OERs) are regarded as the rate-determining step of electrocatalytic overall water splitting, which endow OER electrocatalysts with the advantages of high activity, low cost, good conductivity, and excellent stability. Herein, a facile H2O2-assisted etching method is proposed for the fabrication of Mo-doped ultrathin Co9Se8@NiSe/NF-X heterojunctions with rich Se vacancies to boost electrocatalytic water oxidation. After step-by-step electronic structure modulation by Mo doping and Se vacancy engineering, the self-standing Mo-Co9Se8@NiSe/NF-60 heterojunctions deliver a current density of 50 mA cm-2 with an overpotential of 343 mV and a cell voltage of only 1.87 V at 50 mA cm-2 for overall water splitting in 1.0 M KOH. Our study opens up the possibility of realizing step-by-step electronic structure modulation of nonprecious OER electrocatalysts via heteroatom doping and vacancy engineering.

Combining Valence-to-Core X-ray Emission and Cu K-edge X-ray Absorption Spectroscopies to Experimentally Assess Oxidation State in Organometallic Cu(I)/(II)/(III) Complexes

Abstract: A series of organometallic copper complexes in formal oxidation states ranging from +1 to +3 have been characterized by a combination of Cu K-edge X-ray absorption (XAS) and Cu Kβ valence-to-core X-ray emission spectroscopies (VtC XES). Each formal oxidation state exhibits distinctly different XAS and VtC XES transition energies due to the differences in the Cu Zeff, concomitant with changes in physical oxidation state from +1 to +2 to +3. Herein, we demonstrate the sensitivity of XAS and VtC XES to the physical oxidation states of a series of N-heterocyclic carbene (NHC) ligated organocopper complexes. We then extend these methods to the study of the [Cu(CF3)4]- ion. Complemented by computational methods, the observed spectral transitions are correlated with the electronic structure of the complexes and the Cu Zeff. These calculations demonstrate that a contraction of the Cu 1s orbitals to deeper binding energy upon oxidation of the Cu center manifests spectroscopically as a stepped increase in the energy of both XAS and Kβ2,5 emission features with increasing formal oxidation state within the [Cun+(NHC2)]n+ series. The newly synthesized Cu(III) cation [CuIII(NHC4)]3+ exhibits spectroscopic features and an electronic structure remarkably similar to [Cu(CF3)4]-, supporting a physical oxidation state assignment of low-spin d8 Cu(III) for [Cu(CF3)4]-. Combining XAS and VtC XES further demonstrates the necessity of combining multiple spectroscopies when investigating the electronic structures of highly covalent copper complexes, providing a template for future investigations into both synthetic and biological metal centers.

Square-pyramidal Fe-N4 with defect-modulated O-coordination: Two-tier electronic structure fine-tuning for enhanced oxygen reduction

Abstract: Adjusting the electronic and geometric structures of the Fe-N4 active site using axially coordinated ligands has been shown to be effective for improving the performance of the electrocatalytic oxygen reduction reaction (ORR). Any progress beyond that remains extremely challenging, however. Here, we demonstrate a two-tier electronic modulation strategy using defect-modulated O-coordination to further optimize the electronic structure of the Fe center in iron phthalocyanine (FePc), which realizes greatly enhanced ORR performances. Such an atomically dispersed FePc–O–defect catalyst is achieved using a wet ball-milling process. The mechanochemically constructed active site is a square-pyramidal Fe-N4, with the Fe atom located out of the N4-plane toward an axially coordinated O that is singly bonded to graphene at vacancy defects. The FePc–O–defect catalyst delivers a half-wave potential of 0.929 V with mass specific activity of 76.2 A g−1catalyst at 0.9 V in alkaline media. These values are the highest among the reported non-precious metal electrocatalysts and exceed the baseline with bare O-coordination.

Tuning electronic, magnetic and catalytic behaviors of biphenylene network by atomic doping

Abstract: Recently, a new two-dimensional allotrope of carbon named biphenylene has been experimentally synthesized. First-principles calculations are preformed to investigate the electronic properties of biphenylene and the doping effect is also considered to tune its electronic, magnetic, and catalytic properties. The metallic nature with an n-type Dirac cone is observed in the biphenylene. The magnetism can be induced by Fe, Cl, Cr, and Mn doping. More importantly, the doping position dependence of hydrogen evolution reaction (HER) performance of biphenylene is addressed, which can be significantly improved by atomic doping. In particular, the barrier for HER of Fe doping case is only −0.03 eV, denoting its great potential in HER catalysis.

Identification of a Robust and Durable FeN4Cx Catalyst for ORR in PEM Fuel Cells and the Role of the Fifth Ligand

Abstract: Although recent studies have advanced the understanding of pyrolyzed Fe–N–C materials as oxygen reduction reaction (ORR) catalysts, the atomic and electronic structures of the active sites and their detailed reaction mechanisms still remain unknown. Here, based on first-principles density functional theory (DFT) computations, we discuss the electronic structures of three FeN4 catalytic centers with different local topologies of the surrounding C atoms with a focus on unraveling the mechanism of their ORR activity in acidic electrolytes. Our study brings back a forgotten, synthesized pyridinic Fe–N coordinate to the community’s attention, demonstrating that this catalyst can exhibit excellent activity for promoting direct four-electron ORR through the addition of a fifth ligand such as −NH2, −OH, and −SO4. We also identify sites with good stability properties through the combined use of our DFT calculations and Mössbauer spectroscopy data.

First-principal investigations of electronic, structural, elastic and optical properties of the fluoroperovskite TlLF3 (L = Ca, Cd) compounds for optoelectronic applications

Abstract: In this research work, the Tl-based fluoroperovskite compounds TlLF3 (L = Ca, Cd) were investigated computationally using density functional theory (DFT) to comprehend their structural, elastic, optical, and electronic properties. Computation of the tolerance factor and Birch–Murnaghan curve indicated that the compounds are cubic and structurally stable. The structurally optimized lattice constants and the optimum volume corresponding to the optimum energy were measured. Elastic properties were predicted using the IRelast package, and the results showed that the compounds of interest are mechanically stable, ductile, and anisotropic in nature. The electronic properties (band structures and density of states) show that TlCaF3 and TlCdF3 possess a wide direct bandgap from (X–X) symmetry points of 5.7 eV and 5.6 eV, respectively. The contributions of different elemental states to the valence and conduction bands are evaluated from the total and partial density of states (TDOS & PDOS). Analysis of the optical properties showed that these compounds possess a high refractive index, absorption coefficient, and reflectivity at high energy ranges. The values of the direct bandgap indicated that these compounds are expected to be semiconducting in nature, and their use is primarily considered to be in the semiconductor industries and optoelectronic devices. These compounds are new and have been investigated for the first time using the computational approach, which provides comprehensive insight into their different properties; based on the results, they are recommended as industrial candidates.

Engineering of flat bands and Dirac bands in two-dimensional covalent organic frameworks (COFs): relationships among molecular orbital symmetry, lattice symmetry, and electronic-structure characteristics

Abstract: Two-dimensional covalent organic frameworks (2D-COFs), also referred to as 2D polymer networks, display unusual electronic-structure characteristics, which can significantly enrich and broaden the fields of electronics and spintronics. In this Focus article, our objective is to lay the groundwork for the conceptual description of the fundamental relationships among the COF electronic structures, the symmetries of their 2D lattices, and the frontier molecular orbitals (MOs) of their core and linker components. We focus on monolayers of hexagonal COFs and use tight-binding model analyses to highlight the critical role of the frontier-MO symmetry, in addition to lattice symmetry, in determining the nature of the electronic bands near the Fermi level. We rationalize the intriguing feature that, when the core unit has degenerate highest occupied MOs [or lowest unoccupied MOs], the COF highest valence band [or lowest conduction band] is flat but degenerate with a dispersive band at a high-symmetry point of the Brillouin zone; the consequences of having such band characteristics are briefly described. Multi-layer and bulk 2D COFs are found to maintain the salient features of the monolayer electronic structures albeit with a reduced bandgap due to the interlayer coupling. This Focus article is thus meant to provide an effective framework for the engineering of flat and Dirac bands in 2D polymer networks.

Diabatic States of Molecules.

Abstract: Quantitative simulations of electronically nonadiabatic molecular processes require both accurate dynamics algorithms and accurate electronic structure information. Direct semiclassical nonadiabatic dynamics is expensive due to the high cost of electronic structure calculations, and hence it is limited to small systems, limited ensemble averaging, ultrafast processes, and/or electronic structure methods that are only semiquantitatively accurate. The cost of dynamics calculations can be made manageable if analytic fits are made to the electronic structure data, and such fits are most conveniently carried out in a diabatic representation because the surfaces are smooth and the couplings between states are smooth scalar functions. Diabatic representations, unlike the adiabatic ones produced by most electronic structure methods, are not unique, and finding suitable diabatic representations often involves time-consuming nonsystematic diabatization steps. The biggest drawback of using diabatic bases is that it can require large amounts of effort to perform a globally consistent diabatization, and one of our goals has been to develop methods to do this efficiently and automatically. In this Feature Article, we introduce the mathematical framework of diabatic representations, and we discuss diabatization methods, including adiabatic-to-diabatic transformations and recent progress toward the goal of automatization.

High Thermoelectric Performance in Chalcopyrite Cu1-xAgxGaTe2-ZnTe: Nontrivial Band Structure and Dynamic Doping Effect.

Abstract: The understanding of thermoelectric properties of ternary I-III-VI2 type (I = Cu, Ag; III = Ga, In; and VI = Te) chalcopyrites is less well developed. Although their thermal transport properties are relatively well studied, the relationship between the electronic band structure and charge transport properties of chalcopyrites has been rarely discussed. In this study, we reveal the unusual electronic band structure and the dynamic doping effect that could underpin the promising thermoelectric properties of Cu1-xAgxGaTe2 compounds. Density functional theory (DFT) calculations and electronic transport measurements suggest that the Cu1-xAgxGaTe2 compounds possess an unusual non-parabolic band structure, which is important for obtaining a high Seebeck coefficient. Moreover, a mid-gap impurity level was also observed in Cu1-xAgxGaTe2, which leads to a strong temperature-dependent carrier concentration and is able to regulate the carrier density at the optimized value for a wide temperature region and thus is beneficial to obtaining the high power factor and high average ZT of Cu1-xAgxGaTe2 compounds. We also demonstrate a great improvement in the thermoelectric performance of Cu1-xAgxGaTe2 by introducing Cu vacancies and ZnTe alloying. The Cu vacancies are effective in increasing the hole density and the electrical conductivity, while ZnTe alloying reduces the thermal conductivity. As a result, a maximum ZT of 1.43 at 850 K and a record-high average ZT of 0.81 for the Cu0.68Ag0.3GaTe2-0.5%ZnTe compound are achieved.

Electronic structure and magnetic properties of the perovskites SrTMO3 (TM = Mn, Fe, Co, Tc, Ru, Rh, Re, Os and Ir)

Abstract: Structural, elastic, electronic and magnetic properties of the transition metals based perovskites SrTMO3 (TM = Mn, Fe, Co, Tc, Ru, Rh, Re, Os, Ir) are investigated using advanced exchange-correlation methods based on density functional theory (DFT). The calculated structural parameters are found consistent with the experiments. The elastic properties reveal that these compounds are anisotropic, mechanically stable and ductile except SrMnO3. Electronic properties show that the strong hybridization between TM-d and O-2p states at the Fermi level make these compounds metallic expect SrMnO3 which is half-metal. The electrical resistivity indicates that these compounds are good conductors at room temperature. Magnetic ordering and magnetic susceptibility show that SrMnO3, SrFeO3 and SrTcO3 are G-type antiferromagnetic; SrCoO3, SrRuO3 and SrOsO3 are ferromagnetic, whereas SrRhO3, SrReO3 and SrIrO3 are paramagnetic/non-magnetic compounds. The study also confirms that TM-3d perovskites are strongly correlated electron systems while spin-orbit coupling effect is dominant in TM-5d perovskites.

Enriched d‐Band Holes Enabling Fast Oxygen Evolution Kinetics on Atomic‐Layered Defect‐Rich Lithium Cobalt Oxide Nanosheets

Abstract: Developing a reliable synthesis strategy to concurrently realize electronic structure modulation and two‐dimensionalization of materials is of paramount significance yet still challenging. Herein, a facile and universal strategy is reported to fabricate defect‐abundant atomic‐layered materials with unique electronic structures by mechanical shear‐assisted exfoliation. As a proof‐of‐concept demonstration, atomic‐layered defect‐rich LiCoO2 nanosheets (AD‐LCO) are successfully synthesized, which enable accelerated oxygen evolution kinetics with a substantially decreased oxygen evolution reaction overpotential by 184 and 216 mV at 10 and 50 mA cm–2, respectively. X‐ray absorption spectroscopy suggests that AD‐LCO possesses more d‐band holes and enhanced Co‐O covalency. Density functional theory calculations reveal that the presence of Co lattice vacancies can optimize the adsorption kinetics of intermediates, consequently lowering the energy barrier of the rate‐determining step. Importantly, this method has universal applicability to the fabrication of other ultrathin defect‐rich 2D materials such as BN, WS2, and MoS2. The study has potential implications for offering novel insights into the rational design of ultrathin 2D materials with abundant surface defects for various applications.

Missing theoretical evidence for conventional room-temperature superconductivity in low-enthalpy structures of carbonaceous sulfur hydrides

Abstract: To elucidate the geometric structure of the putative room-temperature superconductor, carbonaceous sulfur hydride (C-S-H), at high pressure, we present the results of an extensive computational structure search of bulk C-S-H at 250 GPa. Using the minima hopping structure prediction method coupled to the GPU-accelerated sirius library, more than 17 000 local minima with different stoichiometries in large simulation cells were investigated. Only 24 stoichiometries are favorable against elemental decomposition, and all of them are carbon-doped ${\mathrm{H}}_{3}\mathrm{S}$ crystals. The absence of van Hove singularities or similar peaks in the electronic density of states of more than 3000 candidate phases rules out conventional superconductivity in C-S-H at room temperature.

Magnetism and charge density wave order in kagome FeGe

Abstract: Electron correlations often lead to emergent orders in quantum materials, and one example is the kagome lattice materials where topological states exist in the presence of strong correlations between electrons. This arises from the features of the electronic band structure that are associated with the kagome lattice geometry: flat bands induced by destructive interference of the electronic wavefunctions, topological Dirac crossings and a pair of van Hove singularities. Various correlated electronic phases have been discovered in kagome lattice materials, including magnetism, charge density waves, nematicity and superconductivity. Recently, a charge density wave was discovered in the magnetic kagome FeGe, providing a platform for understanding the interplay between charge order and magnetism in kagome materials. Here we observe all three electronic signatures of the kagome lattice in FeGe using angle-resolved photoemission spectroscopy. The presence of van Hove singularities near the Fermi level is driven by the underlying magnetic exchange splitting. Furthermore, we show spectral evidence for the charge density wave as gaps near the Fermi level. Our observations point to the magnetic interaction-driven band modification resulting in the formation of the charge density wave and indicate an intertwined connection between the emergent magnetism and charge order in this moderately correlated kagome metal. The observation of band structure features typical of the kagome lattice in FeGe suggests that an interplay of magnetism and electronic correlations determines the physics of this material.