The anomalous Hall effect (AHE) with multi-degree-of-freedom coupling has become a research hot spot in the condensed matter field due to its multiple tunable states, and exploring effective tuning methods for spin, valley, and layer degrees of freedom holds significant research value. Through the first-principles calculations and symmetry analysis, we investigate the properties of bilayer altermagnetic (AM) material Ca(CoN)2, which is protected by S4z symmetry, with a particular focus on the influence of interlayer coupling and sliding on the band structure. For bilayer Ca(CoN)2 with interlayer antiferromagnetic (AFM) coupling, the interlayer opposite spin sublattices can be connected by symmetries such as S4z, classifying it as an AM system. In contrast, systems with interlayer ferromagnetic (FM) coupling belong to the fully compensated ferrimagnetism category. Interlayer sliding breaks the S4z symmetry of the system, thereby controlling the coupling of spin, valley, and layer degrees of freedom. Sliding along the x or y axis breaks the S4z symmetry, inducing opposite valley polarization and layer polarization, which further leads to layer-locked Berry curvature and spin-valley-layer polarized AHE. Bilayer systems with interlayer AFM coupling can switch the spin, valley, and layer degrees of freedom via sliding, while those with interlayer FM coupling can only switch the valley and layer degrees of freedom. This work reveals the sliding rules of bilayer AM systems protected by S4z symmetry and expands the implementation methods for AHE with multi-degree of freedom tunability.

Topological superconductors (TSCs) provide an ideal platform for investigating fundamental quantum phenomena, including non-Abelian anyons and quantum entanglement, positioning them as a key area of focus in contemporary condensed matter physics research. Besides the widely explored transition metal sulfides (TMSs), transition metal nitrides (TMNs) may exhibit exceptional superconducting properties and non-trivial topological quantum numbers. Here, we report a first-principles study of the XMoN4 (X = transition metal elements) family and predict their superconducting and topological properties at ambient pressure. Through the first-principles calculations, we identify 7 stable superconductors, and NbMoN4 exhibits the highest value of 47 K. The nesting of the Fermi surfaces and the flat bands caused by the d-orbitals of metal atoms result in a high density of states, enhancing the pairing of electrons and phonons, thus leading to high Tc. We further study the topological properties and find that the stabilized compound HgMoN4, whose Tc is 35 K at ambient pressure, also exhibits surface states and a Z2 index of (1, 001). Our work predicts a stable superconductor with topological properties under ambient pressure from a constructed family of TMNs, expanding the study of combining the topological properties and superconductivity in bulk-phase materials.

Dynamic control of catalytic activity remains a major challenge for conventional single-atom catalysts (SACs) whose coordination environments are fixed after construction. In this work, CuInP2S6 (CIPS) was employed as a model ferroelectric support to explore how polarization switching modulates catalytic behavior in transition metal single atoms (TM@CIPS) for hydrogen and oxygen evolution reactions (HER and OER). Fifteen transition metals across the 3d-5d series were examined under two polarization states to evaluate the stability and catalytic properties. Polarization switching between upward and downward states was found to dynamically tune catalytic activity, markedly reducing OER overpotentials in systems such as Co@CIPS and Pt@CIPS by optimizing reaction pathways. This enhancement originated from polarization-induced redistribution of interfacial charge, which shifted the d-band center and modified TM-O bonding strength, thereby governing adsorption and reaction energetics. These results establish ferroelectric polarization as an effective strategy for real-time control of catalytic processes and provide fundamental insight for designing next-generation catalysts.

The combination of sliding ferroelectricity and valley properties holds significant potential for the development of next-generation ultrafast processors and memory devices. However, the traditional ferroelectric polarization based on special symmetry can reduce valley polarization. In this study, we propose the across-layer sliding ferroelectricity and robust valley polarization in inversion-symmetric lattices through symmetry analysis and first-principles calculations. In the case of trilayer or more layers, across-layer sliding can induce asymmetry, thereby breaking the overall P symmetry, and ferroelectric polarization occurs. Intriguingly, for the antiferromagnetic even layers, the valley polarization is insensitive to PT symmetry, allowing the coexistence of across-layer sliding ferroelectricity and robust valley polarization. We confirm this in real multilayer YI2 configuration through first-principles calculations. This finding provides a platform for the research sliding ferroelectricity and valleytronics.

Electrides usually have topological properties and high electrical conductivity, so searching for superconducting electrides over a wide range of temperature and pressure is a hot topic in condensed matter physics. Based on high-throughput structure search and the first-principles calculations, we predict that 2H-VN2 is a thermodynamically and dynamically stable electride with the superconducting transition temperature (Tc) of 51 K at ambient pressure. From the calculations of the electronic localization function, it is found that the excess unpaired electrons of the V atoms are likely to exist in the lattice vacancies as interstitial electrons, which makes 2H-VN2 an electride. On the other hand, the existence of irreducible representation at the vacancies also confirms that 2H-VN2 is an electride. Moreover, the flat bands, primarily originating from the V-d orbitals, and the nesting of the Fermi surface induce a high density of states. This enhances the electron-phonon coupling (EPC) strength between the V-d orbitals and the phonon modes associated with the vibrations of N atoms. The calculated EPC strength of 2H-VN2 electride at ambient pressure is 1.06, and the superconducting gap vanishes at 51 K. We find that 2H-VN2 electride has a Tc of 51 K at ambient pressure, which gives a practicable method to connect the superconducting properties and the specificities of electrides in unitary material.

Altermagnets have attracted attention due to their compensating magnetic moments and nonrelativistic spin splitting. However, due to the limitation of the strict symmetry requirements, two-dimensional (2D) altermagnets are still rare, and the regulatory approaches are mostly volatile. Based on the low-energy effective k p model, a general approach to constructing bilayers with fully compensated ferrimagnetism (fFIM) whose properties are like altermagnets has been proposed, and the achieved layer-polarized anomalous Hall effect (LP-AHE) can be manipulated by the ferroelectric (FE) polarization in them. In the bilayers with fFIM, the coupling between FE polarization and interlayer A-type antiferromagnetism induces layer-locked Berry curvature, which provides advantages of antimagnetic interference and nonrelativistic spin splitting. Furthermore, during the symmetry operating of the bilayers with fFIM, the FE polarizations can be changed, and the reversals of the valley indices and the interlayer coupling energies can be achieved. The obtained tunable multiple couplings of spin, valley, and layer degrees of freedom induce LP-AHE in the bilayers with fFIM. Through first-principles calculations, we confirm this mechanism in the bilayer Co2NFCl lattice by performing Manipulatable LP-AHE can be achieved in bilayers with fFIM, which reveals a method for achieving a tunable Hall effect in a broader range of 2D magnets. Mz/ I/C2z symmetry operations.

Based on an effective k·p model, we form breathing Kagome bilayers with two different interlayer antiferroelectric (AFE) couplings, i.e., tail to tail and head to head, to study their magnetic and valley properties. Spin–orbit coupling and magnetic exchange interaction induce valley-layer locking when the bilayer is ferromagnetic, however, spin-layer locking appears for the case of antiferromagnetic states. The inequivalent interlayer antiferroelectric couplings correspond to different magnetic ground states, and the antiferroelectric states can be switched through the breathing process, so the ferroelectric, magnetic, and valley properties can be simultaneously modulated. Through first-principles calculations, we also predict a favorable breathing Kagome bilayer W3Br8, where the above coupling mechanism and tunable layer-locked valley Hall effects can be achieved. Our findings provide an applicable paradigm for achieving ferroelectric–magnetic–valley coupling in a single device, driving the development of next-generation electronic devices.

The efficient separation and purification of high-purity hydrogen is imperative and desirable. We systematically explored the H-2 purification performance of the T-C(3)N2 membrane with and without biaxial compressive (BC) strain and charge engineering by using MD simulations and DFT calculations. We found that the pure T-C3N2 membrane has relatively poor H-2 selectivity as CO2 can also permeate through the membrane, and two modulation methods of BC-strain and charge were thus introduced separately to enhance the H-2 separation performance for the first time. The T-C3N2 membrane with BC-strains modulation (1 %-3%) has excellent H-2 permeance of 1.60 x 10(7)-1.85 x 10(7) GPU at 300 K with 15.6 % enhancement with respect to the pure T-C3N2 membrane. The selectivity of H-2 over gases (CO, N-2, CO2, H2O, CH4) was drastically improved, for example, H-2/CH4 is enhanced from 5.8 x 1020 to 2.1 x 10(36) under 3 % strain engineering. The introduction of charge (1e-3e, 1e(-) -2e(-) ) also enhances the H2 permeance of 1.47 x 10(7)-1.68 x 10(7) GPU and the selectivity at 300 K. In particular, the charge (1e) and (1e- ) modulations exhibit a desired permeance-selectivity trade-off for H-2 purification with the enhancement of 5 % permeability and at least 1.3 times selectivity of H-2 to other gases, respectively. Finally, the synergistic effect of BC-strain and charge on the H-2 separation was studied, and it is much superior to separated BC-strain and charge engineering for H-2 purification, where the H-2 permeance enhances up to 1.86 x 10(7)-1.89 x 10(7) GPU, and the H-2 selectivity at 300 K is also enlarged at least ten times compared with that of the most effective modification of the isolated 2 % BC-strain and 1e charge, indicating synergistic effect further enhances the H-2 separation performance. Therefore, the excellent modulations of appropriate BC-strain and charge engineering, particularly for their synergistic effect make the T-C3N2 membrane a promising candidate for highly permeant and selective H-2 separation and purification that would be easily realized experimentally.

Exploring valley physics in materials with nonhexagonal crystal structures is a promising avenue for advancing the valley degree of freedom. Here, we explore the operability of layer-locked multiple valley Hall effects (VHEs) realized in tetragonal altermagnetic/ferromagnetic monolayers M2SiCX2 (M is a transition metal atom; X = S, Se). Using tetragonal monolayers Cr2SiCX2 as examples, we examine their collinear altermagnetic trivial state and collinear ferromagnetic nontrivial state through first-principles calculations. The net layer-locked VHE and anomalous dual VHE arise from valley-layer coupling, nonzero Berry curvature, and spin splitting. Additionally, the net layer-locked anomalous VHE can also be realized and switched by applying a vertical external electric field or uniaxial strain. Our results provide a platform for layer-locked multiple VHEs and highlight the potential of these materials in low-power-consumption spin valleytronic devices.

In this study, we employed the non-equilibrium Green's function method combined with density functional theory to investigate the spin transport properties of the actinide sandwich phthalocyanine molecule U(Pc)2.This study aims to provide beneficial assistance for the development of actinide phthalocyanine molecular spintronic devices.

The quantum anomalous Hall effect (QAHE) has gained significant attention in recent years due to its potential applications in low-power devices. However, the QAHE still faces the limitations of the relatively small global band gap and low Chern number. In this work, based on the tight-binding (TB) model with magnetic group P3m'1, we propose a mechanism whereby quadratic band crossing induces a stable global band gap which is larger than that formed by the linear band crossing. Additionally, the quadratic band crossing induces topological states with high Chern number when spin-orbit coupling is considered. We also propose monolayer MoTe2F2 to confirm the TB results by performing calculations of first-principles and low-energy k p model. The quadratic band crossing is formed by the hybridization of the orbitals from the Mo and the F atoms. The contributions of the d(xy) and dx(2)-y(2) orbitals at the quadratic band crossing are bigger than their contributions at the linear band crossing, so the global band gap induced by the quadratic band crossing is large. Furthermore, after biaxial strains are applied, the quadratic band crossing is destroyed and it transfers into a linear band crossing, and the global band gap becomes small. The quadratic band crossing can also be manipulated by a vertical electric field, and a phase transition from the QAHE to the anomalous valley Hall effect can be achieved. Our work not only provides a method to discover two-dimensional materials with a large global band gap and high Chern number but also integrates topological electronics and valleytronics, promoting the development of low-power devices.

The design of new high-performance membranes for separation and purification of hydrogen remains highly desirable for industrial applications. Herein, using the density functional theory calculations along with MD simulations, we demonstrated firstly a new 2D membrane based C3N monolayer (D-C3N) with intrinsic pores and then investigated its potential as gas separation membranes for H2 purification. The cohesive energy and ab initio MD simulations confirmed that the D-C3N monolayer is structurally and thermodynamically stable under 1800 K. All considered gas molecules are physisorbed on the D-C3N monolayer with small interaction energy. At room temperature, the D-C3N membrane for H2 gas has high selectivity over other gases such as 1.5×103, 1.8×105, 8.8×109, 1.4×1012, and 1.3×1019 for H2/N2, H2/CO2, H2/O2, H2/H2O, and H2/CH4 at 300K, respectively, and the H2 permeance is as high as 2.2×10-5mol·m-2·s-1·Pa-1, exceeding the industrially acceptable value and most of the carbon-based separation membranes. In addition, MD simulations further confirmed that the defective porous C3N monolayer has ideal selectivity and permeation as a promising separation membrane for H2 purification from other gases for industrial applications.

The layertronics based on the layer degree of freedom are of essential significance for the construction and application of new-generation electronic devices. Although the Hall layer effect has been realized theoretically and experimentally, it is mainly based on topological and antiferromagnetic lattices. On the basis of the low-energy effective kp model, the mechanism of the controllable valley-layer Hall effect (V-LHE) in a bilayer ferromagnetic lattice through interlayer sliding has been proposed. Due to the broken time-reversal and inversion symmetries, the V-LHE based on the valley, layer degree of freedom, ferromagnetism, and ferroelectricity can be predicted. In addition, valley and layer indexes can be controlled by magnetization orientation and slipping, respectively. The mechanism can be demonstrated in the real bilayer CrSI lattice through first-principles calculations. Moreover, V-LHE can be effectively tuned by the perpendicular external electric field in configurations without out-of-plane polarization. These findings provide a new platform for the research of valleytronics and layertronics.

The presence of the intrinsic fields in two-dimensional (2D) materials holds promise for photocatalysts, as it diminishes the band gap requirements of 1.23 eV and accelerates the separation of the photogenerated carriers. Inspired by the extensive application in MA2X4 families, we predict Janus ZMXAY derived from MA2X4 materials to introduce intrinsic fields suitable for photocatalysts from 512 candidates. These monolayers also exhibit high mobilities up to similar to 104 cm2V-1s-1 with strong anisotropy, and are accompanied by the inherent piezoelectric properties. Notably, all monolayers, except Janus SMoPGeAs, SeMoPSiAs, and SeMoPGeAs, demonstrate suitable band gaps (0.88-1.43 eV) and appropriate band edge positions without the need for any external potential to drive spontaneous overall water splitting. It also demonstrates visible optical absorption capacity and high solar-to-hydrogen conversion efficiency (16.06-41.08%). Our work identifies ideal candidates for multifunctional devices and provides theoretical guidance for future experimental research and application development.

The exploration of valley-related physics is essential to the development and refinement of valleytronics. Here, a paradigm called chiral breathing-valley locking (CBVL) is proposed, in which two chiral “breathing” phases are completely locked to their valley indexes. Utilizing first-principles calculations, a two-dimensional (2D) kagome lattice with large spontaneous valley polarization (VP), namely, monolayer Ta3I8, is proposed to realize CBVL. There are two breathing phases with chiral symmetry in Ta3I8, and they can change to each other under some conditions. The valley indexes change between “−K” and “K” along the breathing of the two chiral symmetric phases, so CBVL can be obtained. Remarkably, the VP is up to 199.7 meV, so CBVL can cause the obvious switching of the anomalous valley Hall effect (AVHE). Additionally, a 2D Janus Kagome structure TaI4X4 is constructed to confirm experimentally the feasibility of electric field modulation on the CBVL. The built-in electric field and the breathing mode can mutually influence each other in TaI4X4, which provides a synergistic regulation of the AVHE. Our findings broaden the horizon for exploring AVHE materials and provide a platform for future valleytronic applications.

Motivated by the development of high-performance gas sensors using two-dimensional (2D) nanomaterials, herein using the combination methods of density functional theory (DFT) and nonequilibrium Green’s function (NEGF), the structural, electronic, transport, and gas sensing properties of the B3C2P3 monolayer adsorbed with various gases (NO2, NO, NH3, SO2, H2S, CO2, CO, H2O, O2 and CH2O) have been systematically studied. The NO2 (or NO) molecules were chemically adsorbed (or strong physisorbed) on the B3C2P3 monolayer, while other molecules were weak-physically adsorbed on the substrate. Furthermore, only the NO2 and NO adsorption results in the remarkable change in electronic properties of B3C2P3. The transport properties such as current-voltage (I-V) characteristics and transmission functions indicate the B3C2P3 monolayer is highly sensitive and selective towards NO2 and NO gases. The recovery times of NO2 and NO were calculated to be 2.27 and 0.0785 ms at 300 K, indicating the reusability of the B3C2P3-based NO2 (NO) sensors. The existence of moisture hardly influences the adsorption of NO and NO2 on the B3C2P3 monolayer. Our results indicated that the B3C2P3 monolayer, as a room-temperature reusable gas sensor, is highly sensitive and selective for NO2 and NO detection regardless of the existence of moisture, O2 and CO2.

The anomalous valley Hall effect (AVHE) can be used to explore and utilize valley degrees of freedom in materials, which has potential applications in fields such as information storage, quantum computing and optoelectronics. AVHE exists in two-dimensional (2D) materials possessing valley polarization (VP), and such 2D materials usually belong to the hexagonal honeycomb lattice. Therefore, it is necessary to achieve valleytronic materials with VP that are more readily to be synthesized and applicated experimentally. In this topical review, we introduce recent developments on realizing VP as well as AVHE through different methods, i.e., doping transition metal atoms, building ferrovalley heterostructures and searching for ferrovalley materials. Moreover, 2D ferrovalley systems under external modulation are also discussed. 2D valleytronic materials with AVHE demonstrate excellent performance and potential applications, which offer the possibility of realizing novel low-energy-consuming devices, facilitating further development of device technology, realizing miniaturization and enhancing functionality of them.

The design, electronic and gas-sensing properties of the CN/C3N2 heterostructures with and without the adsorption of H2S, SO2, HF, SOF2, and SO2F2 were systematically investigated by using DFT calculations. All SF6 decomposition gases can physically adsorb on both sides of the CN/C3N2 heterostructure with significant adsorption strength and charge transfer. Although the adsorption of these gases, in general, hardly affects the electronic properties, but can remarkably tune the work function (Φ) of the heterostructure. The CN/C3N2 heterostructure as Φ-type gas sensors has an ultra-high sensitivity for SF6 decomposed gases (at least over 71.2 %), especially for the C3N2 side (at least over 568.7 %), and has relatively low recovery times for HF, H2S, SOF2, and SO2F2 gases at 300 K, indicating the reusability of the heterostructure at room temperature, but much more favorable at 350∼400 K for SO2 gas. Further, the heterostructure as adsorbents for the capture and scavenging of SF6 decomposition gases has high adsorption capacity and strength. Therefore, our findings reveal that the CN/C3N2 heterostructure is a promising candidate as Φ-type gas sensors with high sensitivity and reusability for the detection of SF6 decomposition gases, while as an optimal scavenger for removing these toxic gases.