Tunable abundant valley Hall effect and chiral spin-valley locking in Janus monolayer VCGeN.

It is both conceptually and practically fascinating to explore fundamental research studies and practical applications of two-dimensional systems with the tunable abundant valley Hall effect. In this work, based on first-principles calculations, the tunable abundant valley Hall effect is proved to appear in Janus monolayer VCGeN. When the magnetization is along the out-of-plane direction, VCGeN is an intrinsic ferromagnetic semiconductor with a valley feature.

Novel valley character and tunable quasi-half-valley metal state in Janus monolayer VSiGeP.

The manipulation and regulation of valley characteristics have aroused widespread interest in emerging information fields and fundamental research. Realizing valley polarization is one crucial issue for spintronic and valleytronic applications, the concepts of a half-valley metal (HVM) and ferrovalley (FV) materials have been put forward. Then, to separate electron and hole carriers, a fresh concept of a quasi-HVM (QHVM) has been proposed, in which only one type of carrier is valley polarized for electron and hole carriers.

Electronic-correlation induced sign-reversible Berry phase and quantum anomalous valley Hall effects in Janus monolayer OsClBr.

Topological phase transition can be induced by electronic correlation effects combined with spin-orbit coupling (SOC). Here, based on the first-principles calculations + approach, the influence of electronic correlation effects and SOC on topological and electronic properties of the Janus monolayer OsClBr is investigated. With intrinsic out-of-plane (OOP) magnetic anisotropy, the Janus monolayer OsClBr exhibits a sequence of states, namely, the ferrovalley (FV) to half-valley-metal (HVM) to quantum anomalous valley Hall effect (QAVHE) to HVM to FV states with increasing values.

Spontaneous valley polarization and valley-nonequilibrium quantum anomalous Hall effect in Janus monolayer ScBrI.

Topology and ferrovalley (FV) are two essential concepts in emerging device applications and the fundamental research field. To date, relevant reports are extremely rare about the coupling of FV and topology in a single system. By Monte Carlo (MC) simulations and first-principles calculations, a stable intrinsic FV ScBrI semiconductor with high Curie temperature () is predicted.

Strain-tunable skyrmions in two-dimensional monolayer Janus magnets.

The Dzyaloshinskii-Moriya interaction (DMI), which only exists in noncentrosymmetric systems, plays an important role in the formation of exotic chiral magnetic states. However, the absence of the DMI occurs in most two-dimensional (2D) magnetic materials due to their intrinsic inversion symmetry. Here, by using first-principles calculations, we demonstrate that a significant DMI can be obtained in a series of Janus monolayers of dichalcogenides XSeTe (X = Nb, Re) in which the difference between Se and Te on the opposite sides of X breaks the inversion symmetry.

Two -dimensional semimetal AlSb monolayer with multiple nodal-loops and extraordinary transport properties under uniaxial strain.

Two-dimensional (2D) nodal-loop semimetal (NLSM) materials have attracted much attention for their high-speed and low-consumption transporting properties as well as their fantastic symmetry protection mechanisms. In this paper, using systematic first-principles calculations, we present an excellent NLSM candidate, a 2D AlSb monolayer, in which the conduction and valence bands cross with each other forming fascinating multiple nodal-loop (NL) states. The NLSM properties of the AlSb monolayer are protected by its glide mirror symmetry, which was confirmed using a symmetry-constrained six-band tight-binding model.

High excellent hydrogen evolution characteristics and novel mechanism of two-dimensional tetra-phase OsN and ReN.

It is essential to find a kind of electrocatalyst for hydrogen evolution reduction (HER) comparable with a noble metal that has good conductivity and abundant active sites. Based on systematic searches by first-principles calculations, we discovered two-dimensional transition-metal nitrides, tetra-phase OsN and ReN monolayers, as potential HER electrocatalysts with superior thermodynamic and kinetic stability. They exhibited excellent catalytic activity due to the presence of multiple active sites with a density of 8 × 10 site per cm and an overpotential close to 0.

Magnetic anisotropy and ferroelectric-driven magnetic phase transition in monolayer CrGeTe.

Monolayer CrGeTe (ML-CGT) has attracted broad interest due to its novel electronic and magnetic properties. However, there are still controversies on the origin of its intrinsic magnetism. Here, by exploring the electronic and magnetic properties of ML-CGT, we find that the magnetic shape anisotropy (MSA) is vital for establishing the long-range ferromagnetism, except for the contribution from magnetocrystalline anisotropy energy (MCA).

Anisotropic nodal loop in NiB monolayer with nonsymmorphic configuration.

Two-dimensional (2D) materials featuring a nodal-loop (NL) state have been drawing considerable attention in condensed matter physics and materials science. Owing to their structural polymorphism, recent high-profile metal-boride films have great advantages and the potential to realize a NL. Herein, a 2D NiB monolayer with an anisotropic NL nature is proposed and investigated using first-principles calculations.

A novel spin-valley-coupled nodal-ring semimetal in single-layer TaC.

Nodal-ring semimetals with band crossing are the new type of quantum materials that have attracted considerable interest from scholars for research. In general, the spin-orbit coupling (SOC) effect opens a band gap at the Dirac point. Therefore, finding 2D nodal-ring semimetals with resistance to SOC has more challenges.

Two-dimensional Weyl semi-half-metallic NiCS with a band structure controllable by the direction of magnetization.

Two-dimensional (2D) Weyl semi-half-metals (WSHMs) have attracted tremendous interest for their fascinating properties combining half-metallic ferromagnetism and Weyl fermions. In this work, we present a NiCS3 monolayer as a new 2D WSHM material using systematic first-principles calculations. It has 12 fully spin-polarized Weyl nodal points in one spin channel with a Fermi velocity of 3.

Half-Dirac semimetals and the quantum anomalous Hall effect in Kagome CdN lattices.

Half-Dirac semimetals (HDSs), which possess 100% spin-polarizations for Dirac materials, are highly desirable for exploring various topological phases of matter as low-dimensionality opens unprecedented opportunities for manipulating the quantum state of low-cost electronic nanodevices. The search for high-temperature HDSs is still a current hotspot and yet challenging experimentally. Herein based on first-principles calculations, we propose the realization of Half Dirac semimetals (HDS) in two-dimensional (2D) Kagome transition-metal nitride CdN, which is robust against strain engineering.

Glide Mirror Plane Protected Nodal-Loop in an Anisotropic Half-Metallic MnNF Monolayer.

Two-dimensional (2D) nodal-loop (NL) semimetals have attracted tremendous attention for their abundant physics and potential device applications, whereas the realization of gapless NL semimetals robust against spin-orbit coupling (SOC) remains a big challenge. Recently, breakthroughs have been made with the realization of gapless NL semimetals in 2D half-metallic materials, where NLs were protected by a horizontal mirror plane symmetry. Here we first propose an alternative nonsymmorphic horizontal glide mirror plane symmetry which could protect the NLs in 2D materials.

Two-dimensional honeycomb-kagome TaS: a promising single-spin Dirac fermion and quantum anomalous hall insulator with half-metallic edge states.

Recent experimental success in the realization of two-dimensional (2D) magnetism has invigorated the search for new 2D magnetic materials with a large magnetocrystalline anisotropy, high Curie temperature, and high carrier mobility. Using first-principles calculations, here we predict a novel class of single-spin Dirac fermion states in a 2D Ta2S3 monolayer, characterized by a band structure with a large gap in one spin channel and a Dirac cone in the other with carrier mobility comparable to that of graphene. Ta2S3 is dynamically and thermodynamically stable under ambient conditions, and possesses a large out-of-plane magnetic anisotropy energy and a high Curie temperature (TC = 445 K) predicted from the spin-wave theory.

Discovery of a ferroelastic topological insulator in a two-dimensional tetragonal lattice.

Ferroelasticity and band topology are two intriguing yet distinct quantum states of condensed matter materials. Their coexistence in a single two-dimensional (2D) lattice, however, has never been observed. Here, we found that the 2D tetragonal HfC monolayer allowed simultaneous presence of ferroelastic and topological orders.

Strain-Tuned Topological Insulator and Rashba-Induced Anisotropic Momentum-Locked Dirac Cones in Two-Dimensional SeTe Monolayers.

Rashba spin-orbit coupling (SOC) in topological insulators (TIs) is a very interesting phenomenon and has received extensive attention in two-dimensional (2D) materials. However, the coexistence of Rashba SOC and band topology, especially for materials with a square lattice, is still lacking. Here, by using first-principles calculations, we propose for the first time a SeTe monolayer as a 2D candidate with these novel properties.

Discovery of a novel spin-polarized nodal ring in a two-dimensional HK lattice.

Nodal-ring materials with a spin-polarized feature have attracted intensive interest recently due to their exotic properties and potential applications in spintronics. However, such a type of two-dimensional (2D) lattice is rather rare and difficult to realize experimentally. Here, we identify the first 2D Honeycomb-Kagome (HK) lattice, Mn-Cyanogen, as a new single-spin nodal-ring material by using first-principles calculations.

Nontrivial topology and topological phase transition in two-dimensional monolayer Tl.

Topological insulating material with dissipationless edge states is a rising star in spintronics. While most two-dimensional (2D) topological insulators belong to group-IV or -V elements in a honeycomb lattice, herein, we propose a new topological phase in the 2D hexagonal group-III crystal, h-Tl, based on a tight-binding model and density-functional theory calculation. Analysis of band dispersion reveals a Dirac nodal-ring near the Fermi level, which is attributed to px,y/pz band crossing.

Strain-Induced Quantum Spin Hall Effect in Two-Dimensional Methyl-Functionalized Silicene SiCH₃.

Quantum Spin Hall (QSH) has potential applications in low energy consuming spintronic devices and has become a researching hotspot recently. It benefits from insulators feature edge states, topologically protected from backscattering by time-reversal symmetry. The properties of methyl functionalized silicene (SiCH₃) have been investigated using first-principles calculations, which show QSH effect under reasonable strain.

Discovery of asymmetric NaXBi (X= Sn /Pb) monolayers with non-trivial topological properties.

Two-dimensional (2D) Bi-based films have attracted intensive attention recently. However, materials with spatial asymmetry are rarely reported, impeding their practical application. In the present work, based on density functional theory (DFT) calculations, we propose a new type of 2D asymmetric NaXBi (X = Sn and Pb) monolayer, which can realize the coexistence of a topological phase and the Rashba effect.

NaC monolayer: a novel 2p Dirac half-metal with multiple symmetry-protected Dirac cones.

A Dirac half-metal material, which has a gapped band structure in one spin channel but Dirac cones in the other, combines two intriguing properties of 100% spin polarization and massless Dirac fermions and has recently started to attract increasing attention. In this work, using first-principles calculations we predict that the disodium carbide (Na2C) monolayer is an intrinsic 2p Dirac half-metal material with 12 fully spin-polarized and symmetry-protected Dirac cones, and a slightly gapped (53 meV) spin-polarized nodal line coexisting in one spin channel, leaving the other spin channel insulated with a gap of 1.9 eV.

Quantum spin Hall insulator BiXH (XH = OH, SH) monolayers with a large bulk band gap.

A large bulk band gap is critical for the application of two-dimensional topological insulators (TIs) in spintronic devices operating at room temperature. On the basis of first-principles calculations, we predict BiXH (X = OH, SH) monolayers as TIs with an extraordinarily large bulk gap of 820 meV for BiOH and 850 meV for BiSH, and propose a tight-binding model considering spin-orbit coupling to describe the electronic properties of BiXH. These large gaps are entirely due to the strong spin-orbit interaction related to the pxy orbitals of the Bi atoms of the honeycomb lattice.

Tunable Electronic and Topological Properties of Germanene by Functional Group Modification.

Electronic and topological properties of two-dimensional germanene modified by functional group X (X = H, F, OH, CH₃) at full coverage are studied with first-principles calculation. Without considering the effect of spin-orbit coupling (SOC), all functionalized configurations become semiconductors, removing the Dirac cone at K point in pristine germanene. We also find that their band gaps can be especially well tuned by an external strain.

Correction: Prediction of topological property in TlPBr monolayer with appreciable Rashba effect.

Correction for 'Prediction of topological property in TlPBr monolayer with appreciable Rashba effect' by Min Yuan et al., Phys. Chem.

Bismuth oxide film: a promising room-temperature quantum spin Hall insulator.

Two-dimensional (2D) bismuth films have attracted extensive attention due to their nontrivial band topology and tunable electronic properties for achieving dissipationless transport devices. The experimental observation of quantum transport properties, however, are rather challenging, limiting their potential application in nanodevices. Here, we predict, based on first-principles calculations, an alternative 2D bismuth oxide, BiO, as an excellent topological insulator (TI), whose intrinsic bulk gap reaches up to 0.