Abstract
Intrinsic van der Waals materials layered magnets have attracted much attention, especially the air-stable semiconductor CrSBr. Herein, we carry out a comprehensive investigation of both ...bulk and monolayer CrSBr using the first-principles linear-response method. Through the calculation of the magnetic exchange interactions, it is confirmed that the ground state of bulk CrSBr is A-type antiferromagnetic, while there are five sizable large intralayer exchange interactions with small magnetic frustration, which results in a relatively high magnetic transition temperature of both bulk and monolayer CrSBr. Moreover, the significant electron doping effect and strain effect are demonstrated, with further increased Curie temperature for monolayer CrSBr, as well as an antiferromagnetic to ferromagnetic phase transition for bulk CrSBr. We also calculate the magnon spectra using linear spin-wave theory. These features of CrSBr can be helpful to clarify the microscopic magnetic mechanism and promote the application in spintronics.
We present a comprehensive investigation of the electronic properties of fluorinated monolayer violet phosphorus using first‐principles calculations. Our results reveal a strong dependence of the ...electronic properties on the different fluorine coverages of fluorination. As the fluorine coverage increases, monolayer violet phosphorus undergoes a significant transition from a wide direct bandgap semiconductor to a narrow indirect bandgap semiconductor. Moreover, both semi‐fluorinated and fully fluorinated monolayer violet phosphorus exhibit advantageous semiconducting characteristics, with a tunable bandgap of 0.50 ~ 1.04 eV under biaxial strain ranging from −6% to 6%. Notably, the fully fluorinated monolayer violet phosphorus demonstrates a higher coefficient of light absorption within the visible range. Therefore, our findings highlight the tunability of monolayer violet phosphorus properties through the absorption of various fluorine coverages, providing valuable insights for the design and development of novel semiconductor devices based on this material.
The optical absorption coefficient of fully fluorinated monolayer violet phosphorus is higher than that of monolayer violet phosphorus in the visible spectrum and is enhanced by a factor of two in a specific wavelength range.
The discovery of a new type‐II Dirac semimetal in Ir1−xPtxTe2 with optimized band structure is described. Pt dopants protect the crystal structure holding the Dirac cones and tune the Fermi level ...close to the Dirac point. The type‐II Dirac dispersion in Ir1−xPtxTe2 is confirmed by angle‐resolved photoemission spectroscopy and first‐principles calculations. Superconductivity is also observed and persists when the Fermi level aligns with the Dirac points. Ir1−xPtxTe2 is an ideal platform for further studies on the exotic properties and potential applications of type‐II DSMs, and opens up a new route for the investigation of the possible topological superconductivity and Majorana physics.
A type‐II Dirac semimetal in Ir1−xPtxTe2 with optimized Dirac dispersions is experimentally discovered by angle‐resolved photoemission spectroscopy. The Pt dopant protects the crystal structure holding the Dirac cones and tunes the Fermi level close to the Dirac point. Combining the type‐II Dirac cone, Fermi level tunability, and superconductivity together, Ir1−xPtxTe2 provides an ideal platform for more in‐depth research of type‐II DSMs.
Transition metal niobates MNb2O6 (M = Mn, Fe, Co, Ni) have attracted a lot of interest because of their low dimensional magnetic properties. We carry out a comprehensive study of the electronic and ...magnetic properties of NiNb2O6 and FeNb2O6 using density functional calculations. NiNb2O6 and FeNb2O6 are insulators with band gaps of 2.4 and 1.4 eV, respectively. We find that the state with the lowest total energy of FeNb2O6 is inconsistent with the experimental magnetic ground state. We estimate the exchange parameters for the two compounds and find that this difference is due to the presence of the relatively strong interchain exchange interactions along the a direction in FeNb2O6. We propose that the strong tilt of the magnetic structure, stemming from magnetic anisotropy, offsets the contributions of these interactions to some extent. Thus, unlike NiNb2O6, in order to describe FeNb2O6 correctly by Heisenberg model, the magnetic anisotropy is necessary. Our results indicate that the magnetic anisotropy plays an important role in determining the magnetic ground state for MNb2O6 type compounds.
Display omitted
•The electronic and magnetic properties of NiNb2O6 and FeNb2O6 are studied.•The exchange interaction parameters are estimated and it is found that the exchange interactions between chains are frustrated.•The magnetic anisotropy is necessary in order to correctly obtain the magnetic ground state of FeNb2O6 with the Heisenberg model.
Brownmillerite Ca2Fe2O5 has gained great interest due to its novel properties and wide range of applications. Here, we present a systematically study of the electronic and magnetic properties of ...Ca2Fe2O5 with first-principles calculations. Our calculation results indicate that the valences of both octahedral Fe and tetrahedral Fe are +3. Using the first-principle linear response (FPLR) method, we calculate the magnetic exchange interactions J's. J's are short-range and negligible for the Fe-Fe atomic pair longer than 6 Å. Three relatively large exchange interactions determine that the magnetic ground state is G-type antiferromagnetism, which is consistent with the experimental results. The magnetic transition temperature calculated with our J's is in agreement with the experiment. Based on the obtained magnetic exchange parameters, we calculate the spin-wave dispersion. We also use the FPLR method to calculate the Dzyaloshinskii-Moriya interactions.
•The electronic and magnetic properties of brownmillerite Ca2Fe2O5 are studied.•The magnetic exchange parameters of Ca2Fe2O5 are calculated.•The Néel temperature of Ca2Fe2O5 is calculated by mean field approximation theory.•The spin-wave dispersion of Ca2Fe2O5 is calculated.
Display omitted
•An exchange-transfer mechanism is proposed to understand the contact behaviors of boron sheets on Ag(111).•Unreconstructed clean Ag(111) surface has compressive surface ...stress.•Ag(111) surface covered by monolayer and bilayer boron sheets have opposite surface stress.•Surface stress depends on the atomic relaxation on surface and interfacial charge transfer.•Al(111) and Au(111) substrates are proposed as two potential substrates for growing boron sheets beyond a single layer.
The experimental synthesis of the boron sheets beyond a single layer is a challenge in low-dimensional physics, and the interaction mechanism between multilayered boron sheets and metal substrates remains unclear. Here, we propose an exchange-transfer mechanism to understand the distinctively different behaviors of monolayer (ML) and bilayer (BL) borophene contacts on Ag(111) based on first-principles calculations. It is shown that threefold enhancement of the tensile surface stress in the BL borophene plays a vital role in this exchange-transfer mechanism, while released compressive surface stress was found for ML borophene covers on Ag(111). The feature of the mechanism is that the dz2 electrons on the Ag(111) transferring to the pz orbital of the bridged B pillars are compensated mainly by the electrons from the bottom B px + py orbitals. This mechanism causes more interaction density states between the Ag(111) and BL borophene while not found in the ML borophene. In addition, the analysis of surface stress indicates that it has high feasibility of growing BL borophene by chemical vapor deposition method on Al and Au substrates.
Display omitted
Two-dimensional (2D) layered semiconductors with nonlinear optical properties hold great attention due to their potential in electronic-photonic integrated circuits. However, the ...development of 2D nonlinear optical semiconductors is hindered by limitations such as low nonlinear polarization strength, low carrier mobility, and narrow light absorption window. In this study, we investigate the 2D SnP2X6 family (X=S, Se, Te), a van der Waals material that exhibits nonlinear optical properties and high carrier mobility. In which, 1L SnP2Te6 demonstrates a remarkable carrier mobility ranging from 886 to 1024 cm2 v−1 s−1 at room temperature, comparable to that of black phosphorus. The introduction of metal vacancies in 2D SnP2X6 structure leads to asymmetric geometric configurations, resulting in pronounced anisotropy in electronic properties, while not found in the 2D Sn2P2X6. The distortion at the Sn4+ site in the 2D SnP2X6 (compared to the Sn2+ in pristine SnP2X6) not only leads to the dominance of hole carriers but also further enhances the structural asymmetry, thereby inducing pronounced electrical and optical anisotropy. Our findings provide direct theoretical evidence supporting the utilization of the 2D SnP2X6 family as promising nonlinear optical crystals.
Anisotropic magnetic exchange interactions lead to a surprisingly rich variety of the magnetic properties. Considering the spin orbit coupling (SOC) as perturbation, we extract the general expression ...of a bilinear spin Hamiltonian, including isotropic exchange interaction, antisymmetric Dzyaloshinskii-Moriya (DM) interaction and symmetric \(\Gamma \) term. Though it is commonly believed that the magnitude of the DM and \(\Gamma \) interaction correspond to the first and second order of SOC strength \(% \lambda \) respectively, we clarify that the term proportional to \(\lambda ^{2}\) also has contribution to DM interaction. Based on combining magnetic force theorem and linear-response approach, we have presented the method of calculating anisotropic magnetic interactions, which now has been implemented in the open source software WienJ. Furthermore, we introduce another method which could calculate the first and second order SOC contribution to the DM interaction separately, and overcome some shortcomings of previous methods. Our methods are successfully applied to several typical weak ferromagnets for \(3d\), \(4d\) and \(5d\) transition metal oxides. We also predict the conditions where the DM interactions proportional to \(\lambda \) are symmetrically forbidden while the DM interactions proportional to \(\lambda ^{2}\) are nonzero, and believe that it is widespread in certain magnetic materials.
PDF
