Layered van der Waals materials are exciting as they often host multiple, competing electronic phases. This article reports the experimental observation of the coexistence of insulating and metallic phases deep within the commensurate charge density wave phase in high-quality devices of few-layer $1\mathrm{T}\text{−}{\mathrm{TaS}}_2$. Through detailed conductance fluctuation spectroscopy of the electronic ground state, we establish that the mixed phase consists of insulating regions surrounded by one-dimensional metallic domain walls. We show that the electronic ground state of $1\mathrm{T}\text{−}{\mathrm{TaS}}_2$ can be affected drastically by strain, eventually leading to the collapse of the Mott gap in the commensurate charge density wave phase. Our study resolves an outstanding question, namely the effect of the interlayer coupling strength on the electronic phases in layered van der Waals materials.

Introducing magnetic exchange interaction into topological insulators is known to break the time-reversal symmetry and to open a gap at the Dirac point in the otherwise gapless topological surface states. This allows various novel topological quantum phenomena to be attained, including the quantum anomalous Hall effect and can lead to the emergence of the axion insulator phase. Among the different approaches, magnetic doping is an effective, but still experimentally challenging pathway to provide the magnetic exchange interaction. Here we demonstrate that epitaxial deposition of Co and Mn magnetic atoms onto the (0001) surface of the ${\mathrm{BiSbTeSe}}_2$ topological insulator with a coverage between 0.6 and 3 atoms per surface cell performed in a finely tuned temperature range of ${300}^{\circ }$–${330}^{\circ }\mathrm{C}$ leads to the substitution of pnictogen atoms in the surface layer with magnetic atoms and to the formation of a two-dimensional magnetic phase with out-of-plane magnetization as proved by SQUID magnetometry. This magnetic layer is responsible for the appearance of a gap in the Dirac surface state as revealed by laser-based microfocused angle-resolved photoelectron spectroscopy. Our measurements have shown that the gap exists within the temperature range of 15–100 K, where the out-of-plane magnetization persists. The presented experimental results are supported by relativistic ab initio calculations.

In alignment with the efforts on miniaturizing the components of electronic devices with enhanced performance, we investigate a dielectric nanocapacitor (DNC) based on metallic borophene electrodes separated with insulating hexagonal boron nitride (h-BN) monolayers ($n=1–5$). The capacitive performance of the proposed DNC as a function of applied electric field ($\vec{E}$) and thickness of the dielectric material is examined by using ab initio methods. The borophene plates and h-BN monolayers are commensurate and coupled only with van der Waals interaction, which constitutes an ideal configuration as a DNC. It is found that a single h-BN layer is not thick enough as a spacer to hinder quantum tunneling effects, and similar to the case with no insulating layer, borophene electrodes are shorted. Being effective from two h-BN layers, the charge separation on borophene plates is attained via $\vec{E}$ in the vertical direction. The capacitance of the DNC rapidly saturates at $\vec{E}\ge 0.1\mathrm{V}/\AA$ and reaches its maximum value of $0.77\mu \mathrm{F}/{\mathrm{cm}}^2$ for $n=2$. The capacitance decreases with an increasing number of insulating layers as the distance between electrodes enlarges and shows a similar trend that is expected from the classical Helmholtz model. Our results suggest metallic and lightweight borophene and insulating h-BN monolayers as ideal constituents for the DNC design.

In this study, using symmetry analysis, we reveal that symmetry-enforced three-nodal surfaces (NSs) and Dirac nodal-line (DNL) net phonons can coexist in two candidate space groups (SGs)—with SG Nos. 61 and 205—out of 230 SGs. The phononic DNL net in SGs 61 and 205 contains three phononic DNLs, which share phononic nodal point $R$ in the momentum space and lie at the hinge between two of the three $k_i(i=x,y,z)$ planes. More interestingly, using first-principle calculations, we find that the realistic materials ZnSb (with SG No. 61) and ${\mathrm{RuS}}_2$, ${\mathrm{P}}_2\mathrm{Pt}$, and ${\mathrm{OsS}}_2$ (with SG No. 205) exhibit three NSs and DNL net phonons. In addition, we report that obvious phononic surface states can be observed in these mentioned realistic materials and will benefit their experimental detection. We hope that the proposed realistic materials can be viewed as ideal platforms to realize the DNL net and three-NSs phonons in solid-state materials.

A metal oxide support and a catalytically active metal are the two main ingredients for complex catalysts used in heterogeneous catalysis. The gas environment can change the catalyst during the reaction, modifying its structural and electronic properties. Here, we use monochromated electron energy loss spectroscopy (EELS) to reveal hydrogen-pressure-dependent changes of the electronic structure at the Pd/rutile-${\mathrm{TiO}}_2$ interface in an environmental transmission electron microscope (ETEM). Hydrogen-induced changes are observed in rutile-${\mathrm{TiO}}_2$ within $2\mathrm{nm}$ from the interface at 10 Pa of hydrogen pressure, in the Ti $L_{3,2}$ EEL spectra. Lower pressures such as 1 Pa show no changes in the EEL spectra. We attribute the observed changes in the EEL spectra to hydrogen-induced defects accumulating in the vicinity of the interface. Based on DFT calculations, we developed a thermodynamic multistate defect (TMD) model of the interface and the bulk of the rutile-${\mathrm{TiO}}_2$. This TMD model predicts high concentrations of positively charged defects accumulating at the interface. The presence of the Schottky barrier stabilizes these defects by significantly lowering their formation energy. Our findings provide important insights into catalytic processes taking place at metal/metal oxide interfaces in hydrogen gas environments.

Cluster-assembled metallic films show interesting electrical properties, both in the near-percolation regime, when deposited clusters do not form a complete layer yet, and when the film thickness is well above the electrical percolation threshold. Correctly estimating their electrical conductivity is crucial, but, particularly for the latter regime, standard theoretical tools are not quite adequate. We therefore developed a procedure based on an atomically informed mesoscopic model in which ab initio estimates of electronic transport at the nanoscale are used to reconstruct the conductivity of nanogranular gold films generated by molecular dynamics. An equivalent resistor network is developed, appropriately accounting for ballistic transport. The method is shown to correctly capture the nonmonotonic behavior of the conductivity as a function of the film thickness, namely, a signature feature of nanogranular films.

A combined approach using first-principles calculations and spin dynamics simulations is applied to study $\mathrm{Ni}/{\mathrm{Ir}}_n/\mathrm{Pt}\left(111\right)$ ($n=0,1,2$) films. The lowest-energy states are predicted to be spin spirals but with a minute (of the order of a few $\mu \mathrm{eV}/\mathrm{atom}$) energy difference with skyrmionic states. The spontaneous low-temperature skyrmions, with $\sim 15$ nm to $\sim 35$ nm size, arise from a large Dzyaloshinskii-Moriya (DM) and Heisenberg exchange interactions ratio and, in particular, from a large in-plane DM vector component for nearest neighbors. The skyrmions become larger and more dispersed with the enhancement of the Ir buffer thickness. Also, with increasing $n$, the skyrmions' stability decreases when an external magnetic field is applied or the temperature is raised. For $n=0$ and $n=1$, we find that metastable skyrmioniums can occur, which are characterized by a slightly lower stability with respect to the external fields and larger critical currents, compared to skyrmions.

We present a detailed study of the electronic and magnetic interactions of ${\mathrm{Ba}}_2{\mathrm{CoO}}_4$, structurally very uncommon because of the isolated ${\mathrm{CoO}}_4$ distorted tetrahedral coordination. We show the presence of $\mathrm{Co}\left(d\right)-\mathrm{O}\left(p\right)$ hybridized states characterized by spin polarized oxygen atoms, with their magnetic moments parallel to that on Co. The calculated isotropic exchange interaction parameters, which include the contributions from ligand spins, demonstrate the presence of a three-dimensional (3D) network of magnetic couplings that are partially frustrated in the identified magnetic ground state. Our results indicate that the dominant indirect exchange mechanism responsible for this ground state is mediated by O atoms along the Co–O$\cdots$O–Co path.

The identification of materials supporting complex, tunable magnetic order at ambient temperatures is foundational to the development of new magnetic device architectures. We report the design of $\mathrm{Mn}{}_{2}XY$ tetragonal inverse Heusler alloys that are capable of hosting magnetic antiskyrmions whose stability is sensitive to elastic strain. We first construct a universal magnetic Hamiltonian capturing the short- and long-range magnetic order which can be expected in these materials. This model reveals critical combinations of magnetic interactions that are necessary to approach a magnetic phase boundary, where the magnetic structure is highly susceptible to small perturbations such as elastic strain. We then computationally search for quaternary $\mathrm{Mn}{}_2(X_1,X_2)Y$ alloys where these critical interactions may be realized and which are likely to be synthesizable in the inverse Heusler structure. We identify the $\mathrm{Mn}{}_2\mathrm{Pt}{}_{1-z}{X}_z\mathrm{Ga}$ family of materials with $X=$ Au, Ir, Ni as an ideal system for accessing all possible magnetic phases, with several critical compositions where magnetic phase transitions may be actuated mechanically.

We use the available transport measurements in the literature to develop a dataset for the likely amount of disorder in semiconductor (InAs and InSb) materials which are used in fabricating the superconductor-semiconductor nanowire samples in the experimental search for Majorana zero modes. Using the estimated disorder in direct Majorana simulations, we conclude that the current level of disorder in semiconductor Majorana nanowires is at least an order of magnitude higher than that necessary for the emergence of topological Majorana zero modes. In agreement with existing results, we find that our estimated disorder leads to the occasional emergence of trivial zero modes, which can be post-selected and then further fine-tuned by varying system parameters (e.g., tunnel barrier), leading to trivial zero-bias conductance peaks in tunneling spectroscopy with $\sim 2e^2/h$ magnitude. Most calculated tunnel spectra in these disordered systems, however, manifest essentially no significant features, which is also consistent with the current experimental status, where zero-bias peaks are found only occasionally in some samples under careful fine-tuning.

Interlayer orbital hybridization plays a crucial role in the design of optoelectronic, photovoltaic, and photocatalysis devices based on stacked van der Waals (vdW) materials. In this work, using first-principles calculations, we report an enhancement phenomenon of interlayer orbital hybridization at MoSSe/tellurene (Te) vdW interface. The charge density of two components in MoSSe/Te are overlapped at conduction band minimum, which features highly efficient excitonic solar cells with power conversion efficiency (PCE) up to 22.6%. Moreover, the MoSSe/Te heterostructure exhibits a remarkable absorbance coefficient up to $\sim 7\times {10}^{{}^5}{\mathrm{cm}}^{-1}$ from ultraviolet (UV) to visible light region. Combined with the nonequilibrium Green's function (NEGF) method, the calculated maximum photoinduced current density under visible light radiation from the heterobilayer is up to 3.2 mA ${\mathrm{cm}}^{-2}$, which remarkably exceeds those of the thin-film silicon and bilayer MoSSe devices. Finally, the superior photocatalytic activities are revealed and discussed. Our present findings confirm that the heterostacking of Janus MoSSe and Te could be strikingly helpful for optoelectronic, photovoltaic, and photocatalytic applications.

Tin monosulfide (SnS) usually exhibits $p$-type conduction due to the low formation enthalpy of acceptor-type defects, and as a result, $n$-type SnS thin films have never been obtained. In this paper, we realize $n$-type conduction in SnS thin films by using radiofrequency-magnetron sputtering with Cl doping and a sulfur plasma source during deposition. Here, $n$-type SnS thin films are obtained at all the substrate temperatures employed in this paper (221–341 °C), exhibiting carrier concentrations and Hall mobilities of $\sim 2\times {10}^{18}\mathrm{c}{\mathrm{m}}^{–3}$ and $0.1–1\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{–1}{\mathrm{s}}^{–1}$, respectively. The films prepared without a sulfur plasma source, on the other hand, exhibit $p$-type conduction despite containing a comparable amount of Cl donors. This is likely due to a significant number of acceptor-type defects originating from sulfur deficiency in $p$-type films, which appears as a broad optical absorption within the band gap. We demonstrate $n$-type SnS thin films in this paper for the realization of SnS homojunction solar cells, which are expected to have a higher conversion efficiency than the conventional heterojunction SnS solar cells.

By an extensive structural search using the minima hopping method together with the charge equilibration via neural network technique (CENT) artificial neural network potential, we find several novel lithium chloride structures. Besides reproducing the known low energy phases of LiCl, the structural search reveals 86 new phases of which 42 are energetically lower than the rocksalt phase. We classify our structures based on their structural similarities. While many of them can be considered as polytypes of known structures, there are also entirely unexpected low-density polymorphs that contain empty cages and channels.

ZnO thin films in nanorod (NR) and nanoflower (NF) morphologies were used as photoelectrode scaffolds for efficient visible-light-driven photoelectrochemical (PEC) water splitting process, where their decoration with copper indium gallium sulfide (CIGS) and indium sulfide (${\mathrm{In}}_2{\mathrm{S}}_3$) layers resulted in significant PEC performance enhancement. ZnO NF/CIGS/${\mathrm{In}}_2{\mathrm{S}}_3$ photoelectrodes exhibited a remarkably high PEC efficiency ($\sim 6.0\%$ applied bias photon-to-current efficiency, 83% incident photon-to-current efficiency) due to the negligible dark current, while ZnO NR/CIGS/${\mathrm{In}}_2{\mathrm{S}}_3$ generated a photocurrent density of $30.0\mathrm{mA}.\mathrm{c}{\mathrm{m}}^{–2}$ at 0.4 V (vs Ag/AgCl), being one of the highest performances reported in the literature for copper-based chalcopyrite photoelectrodes so far. The interfacial photoelectrode-electrolyte charge transport dynamics, investigated via intensity-modulated photocurrent spectroscopy, exhibited a sevenfold increase in charge transfer efficiencies with a significant drop in surface recombination kinetics for ZnO NF after CIGS/${\mathrm{In}}_2{\mathrm{S}}_3$ decoration. The obtained results show consistency with numerically modeled electric field distribution profiles and electron paramagnetic resonance results of ZnO NF, rationalizing the enhanced charge transfer rates for decorated samples and confirming the defect passivating nature of CIGS/${\mathrm{In}}_2{\mathrm{S}}_3$.

We investigate the structural stabilities of ${\mathrm{CaCu}}_5$-type derived structures $({\mathrm{Sm}}_{m-n}{T}_{5m+2n}, T=\mathrm{Fe},\mathrm{Co})$ and predict metastable structures with the dumbbell cluster expansion model in which the dumbbell atoms are regarded as virtual single atoms. The metastable structures are concentrated from $n/m=1/3$ to $1/2$, suggesting the existence of compounds with high magnetization. The disordered ${\mathrm{TbCu}}_7$-type structures are stabilized by the configurational entropy of the dumbbell clusters. The estimated solubility limits of the $T\text{−}T$ dumbbell are close to the experimental results. The difference in the phase diagram for the Sm-Fe and Sm-Co systems is explained from their effective cluster interactions.

While the shear banding is a ubiquitous feature for metallic glasses and other disordered solids, the underlying material softening mechanism is still an open question requiring physical interpretation at atomic level. Here, through a set of atomistic simulations, we clarify the origin of flow localization, i.e., the birth of a shear band. The local thermal temperature induced by atomic vibration and configurational temperature attributed to structural disordering are proposed to quantify critical degree of thermal and configurational softening, respectively. The comparison between configurational softening and thermal softening being two potential causes for shear banding emergence is then examined at atomic scale. Numerical evidence from atomistic simulations indicates that configurational-softening-induced strain burst is the dominant instability mode as evidenced through a very large value of configurational temperature rise that commensurate with glass transition temperature. It is also found that configurational softening takes precedence over thermally activated ones. Configurational softening is thus conceivably acting as the root cause for the onset of strain localization and shear banding, while the subsequent thermal softening is its consequence. These results provide important insights into the puzzle about the material weakening mechanism underlying shear banding.

Computational searches for new materials are naturally turning from binary systems, to ternary and other multicomponent systems, and beyond. Here, we select the industrially relevant metals titanium and aluminium and report the results of an extensive structure prediction study on the ternary titanium-carbon-oxygen (Ti-C-O) and aluminium-carbon-oxygen (Al-C-O) systems. We map out the full phase stability of Ti-C-O and Al-C-O compounds using first-principles calculations, through simple, efficient, and highly parallel random structure searching in conjunction with techniques based on complex network theory. These phase stabilities emerge naturally from our ‘data agnostic’ approach, in which we map stable compounds without recourse to structural databases or other prior knowledge. A surprising find is the predicted ambient pressure stability of octet-rule-fulfilling titanium and aluminium carbonate: $\mathrm{Ti}{\left({\mathrm{CO}}_3\right)}_2$ and ${\mathrm{Al}}_2{\left({\mathrm{CO}}_3\right)}_3$, neither of which has to our knowledge been synthesized before. These materials could potentially act as carbon sequestering compounds. Our searches discover several additional stable and metastable ternary compounds supported by the Ti-C-O and Al-C-O systems.

Mott transition has been realized in atomically thin monolayers (MLs) of two-dimensional (2D) semiconductors ($\mathrm{W}{\mathrm{S}}_2$) via optically excited carriers above a critical carrier density through many-body interactions. The above nonlinear optical transition occurs when excited electron hole pairs in the ML $\mathrm{W}{\mathrm{S}}_2$ continuum heavily interact with each other followed by transformation into a collective electron-hole-plasma phase, by losing their identity as individual quasiparticles. This is manifested by the alluring redshift-blueshift crossover phenomena of the excitonic peaks in the emission spectra, resulting from the synergistic attraction-repulsion processes at the Mott transition point. A systematic investigation of many-body effects is reported on ML $\mathrm{W}{\mathrm{S}}_2$, while considering the modulated dielectric screening of three different substrates, viz., silicon dioxide, sapphire, and gold. Substrate doping effects on ML $\mathrm{W}{\mathrm{S}}_2$ are discussed using the Raman fingerprints and photoluminescence spectral weight, which are further corroborated using theoretical density functional theory calculations. Further, the substrate-dependent excitonic Bohr radius of ML $\mathrm{W}{\mathrm{S}}_2$ is extracted via modeling the emission energy shift with Lennard-Jones potential. The variation of the Mott point, as well as the excitonic Bohr radius, is explained via the substrate-induced dielectric screening effect for both dielectric substrates, which is, however, absent in ML $\mathrm{W}{\mathrm{S}}_2$ on Au. In this paper, we therefore reveal diverse many-body ramifications in 2D semiconductors and offer decisive outlooks on selecting impeccable substrate materials for innovative device engineering.