RESUMEN
Confining interacting particles in one-dimension (1D) changes the electronic behavior of the system fundamentally, which has been studied extensively in the past. Examples of 1D metallic systems include carbon nanotubes, quasi-1D organic conductors, metal chains, and domain boundary defects in monolayer thick transition-metal dichalcogenides such as MoSe2. Here single and bundles of Mo6Se6 nanowires were fabricated through annealing a MoSe2 monolayer grown by molecular-beam epitaxy on graphene. Conversion from two-dimensional (2D) MoSe2 film to 1D Mo6Se6 nanowire is reversible. Mo6Se6 nanowires form preferentially at the Se-terminated zigzag edges of MoSe2 and stitch to it via two distinct atomic configurations. The Mo6Se6 wire is metallic and its length is tunable, which represents one of few 1D systems that exhibit properties pertinent to quantum confined Tomonaga-Luttinger liquid, as evidenced by scanning tunneling microscopic and spectroscopic studies.
RESUMEN
Unraveling the formation mechanism of hydroxyl radicals (OHË) is one of the outstanding issues in photocatalytic reactions, where 5,5-dimethyl-1-pyrroline N-oxide (DMPO) is widely utilized as a trapping agent to detect OHË radicals in experiments. In this study, we carry out density functional theory calculations to reveal the origin and formation process of OHË radicals by investigating the interaction of water with DMPO on a rutile TiO2(110) surface. Our results clearly show that the OHË radicals trapped by DMPO stem from water upon illumination. The charge compensation mechanism dominates the formation of DMPO-OH from the reaction between DMPO and water on the rutile TiO2(110) surface. These findings provide new insights into the photocatalytic mechanism and may achieve new frontiers in photocatalytic research.
RESUMEN
The topological quantum states in two-dimensional (2D) materials are fascinating subjects of research, which usually highlight electron-related systems. In this work, we present a recipe that leads to Dirac phonon states with a quantized valley Berry phase in 2D hexagonal lattices by first-principles calculations. We show that candidates possessing the 3-fold rotational symmetry at the corners of the hexagonal Brillouin zone host valley Dirac phonons, which are guaranteed to remain intact with respect to perturbations. We identify that such special topological features populated by Dirac phonons can be realized in various 2D materials. In particular, the monolayer CrI3, an attractive 2D magnetic semiconductor with exotic applications in spintronics, is an ideal platform to investigate nontrivial phonons in experiments. We further confirm that the phonon Berry phase is quantized to ± π at two inequivalent valleys. The phonon edge states terminated at the projection of phonon Dirac cones are clearly visible. This work demonstrates that 2D hexagonal lattices with attractive valley Dirac phonons will extend the knowledge of valley physics, providing wide applications of topological phonons.
RESUMEN
The realization of topological quantum states in devices is an important subject. According to whether or not the time-reversal symmetry is broken, topological materials can be classified into magnetic and nonmagnetic ones. In particular, magnetic topological materials are of importance, in which the coexistence of nontrivial band topology and magnetic orders gives exotic spintronics-related applications. However, experimental observations of magnetic topological quantum states are extremely difficult. In this Perspective, we review the recent progress to explore and design magnetic topological oxides such as topological semimetals and three-dimensional quantum anomalous Hall insulators, which are robustly stable against oxidation at ambient conditions. Most of these materials possess high Curie temperatures and are widely used in industrial applications, stimulating considerable experimental interest. Moreover, further discussions related to the topological classification and topological transitions are also present.
RESUMEN
A mirror twin-domain boundary (MTB) in monolayer MoSe2 represents a (quasi) one-dimensional metallic system. Its electronic properties, particularly the low-energy excitations in the so-called 4|4P-type MTB, have drawn considerable research attention. Reports of quantum well states, charge density waves, and the Tomonaga-Luttinger liquid (TLL) have all been made. Here, by controlling the lengths of the MTBs and employing different substrates, we reveal by low-temperature scanning tunneling microscopy/spectroscopy, Friedel oscillations and quantum confinement effects causing the charge density modulations along the defect. The results are inconsistent with charge density waves. Interestingly, for graphene-supported samples, TLL in the MTBs is suggested, whereas that grown on gold, an ordinary Fermi liquid, is indicated.
RESUMEN
Monolayer (ML) tungsten ditelluride (WTe2) is a well-known quantum spin Hall (QSH) insulator with topologically protected gapless edge states, thus promising dissipationless electronic devices. However, experimental findings exhibit the fast oxidation of ML WTe2 in ambient conditions. To reveal the changes of topological properties of WTe2 arising from oxidation, we systematically study the surface oxidation reaction of ML 1T'-WTe2 using first-principles calculations. The calculated results indicate that the fast oxidation of WTe2 originates from the existence of H2O in air, which significantly promotes the oxidation of ML 1T'-WTe2. More importantly, this low-coverage oxidized WTe2 loses its topological features and is changed into a trivial insulator. Furthermore, we propose a fully oxidized ML WTe2 that can still possess the QSH insulator states. The topological phase transition induced by oxidation provides exotic insight into understanding the topological features of layered transition-metal dichalcogenide materials.
RESUMEN
Using first-principles calculations, we predict a family group of two-dimensional semimetals MX (M = Pd, Pt; X = S, Se, Te), which has a zig-zag type mono-layer structure in the Pmma (no. 41) layer group. Band structure analysis reveals that node-line features are caused by band inversion and the inversion exists even in the absence of spin-orbital-coupling. First-principles calculations show the robust lattice stability of these predicted materials. This work provides the possibility of making a group of novel two-dimensional materials with semimetal features.
RESUMEN
Weyl semimetals have recently attracted enormous attention due to their unusual features. So far, this novel state has been predicted theoretically and confirmed experimentally in several materials, such as HgTe, LaPtBi, Y2Ir2O7, TaAs, TaP, NbAs, NbP and HgCr2Se4. Doping plays an important role in the research of condensed-matter materials. However, its influence on the Weyl semimetal has been little investigated. Here, we present detailed first-principles and theoretical studies on HgCr2Se4 with doping of Te atoms at the Se sites. A special case where only one pair of crossing points locates at the Fermi level is realized in HgCr2Se3.5Te0.5 where one of the Se atoms in the primitive unit cell is replaced by a Te atom. A further study of k·p theory shows that the two points constitute a pair of Weyl nodes with opposite chiralities in the momentum space, and only one edge state and one single Fermi arc are obtained at each boundary of a film. Moreover, through investigations and analyses of different doping cases of HgCr2Se3.5Te0.5, we find that when the type of doping induces inversion symmetry or positional disorder, the Weyl nodes transform into Dirac points resulting in a change from a Weyl semimetal to a Dirac semimetal.