اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدRelativistic exchange interactions in CrX$_3$ (X=Cl, Br, I) monolayers
68
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
It has been predicted theoretically and indirectly confirmed experimentally that single-layer CrX$_3$ (X=Cl, Br, I) might be the prototypes of topological magnetic insulators (TMI). In this work, by using first-principles calculations combined with atomistic spin dynamics we provide a complete picture of the magnetic interactions and magnetic excitations in CrX$_3$. The focus is here on the two most important aspects for the actual realization of TMI, namely the relativistic magnetic interactions and the finite-size (edge) effects. We compute the full interaction tensor, which includes both Kitaev and Dzyaloshinskii-Moriya terms, which are considered as the most likely mechanisms for stabilizing topological magnons. First, we instigate the properties of bulk CrI$_3$ and compare the simulated magnon spectrum with the experimental data [Phys. Rev. X 8, 041028 (2018)]. Our results suggest that a large size of topological gap, seen in experiment ($approx$ 4 meV), can not be explained by considering pair-wise spin interactions only. We identify several possible reasons for this disagreement and suggest that a pronounced magneto-elastic coupling should be expected in this class of materials. The magnetic interactions in the monolayers of CrX$_3$ are also investigated. The strength of the anisotropic interactions is shown to scale with the position of halide atom in the Periodic Table, the heavier the element the larger is the anisotropy. Comparing the magnons for the bulk and single-layer CrI$_3$, we find that the size of the topological gap becomes smaller in the latter case. Finally, we investigate finite-size effects in monolayers and demonstrate that the anisotropic couplings between Cr atoms close to the edges are much stronger than those in ideal periodic structure. This should have impact on the dynamics of the magnon edge modes in this class of materials.
قيم البحث
اقرأ أيضاً
We present a comprehensive theory of the magnetic phases in twisted bilayer Cr-trihalides through a combination of first-principles calculations and atomistic simulations. We show that the stacking-dependent interlayer exchange leads to an effective
moire field that is mostly ferromagnetic with antiferromagnetic patches. A wide range of noncollinear magnetic phases can be stabilized as a function of the twist angle and Dzyaloshinskii-Moriya interaction as a result of the competing interlayer antiferromagnetic coupling and the energy cost for forming domain walls. In particular, we demonstrate that for small twist angles various skyrmion crystal phases can be stabilized in both CrI$_3$ and CrBr$_3$. Our results provide an interpretation for the recent observation of noncollinear magnetic phases in twisted bilayer CrI$_3$ and demonstrate the possibility of engineering further nontrivial magnetic ground states in twisted bilayer Cr-trihalides.
To understand the magnetic property of layered van der Waals materials CrOX (X = Cl, Br), we performed the detailed first-principles calculations for both bulk and monolayer. We found that the charge-only density functional theory combined with the e
xplicit on-site interaction terms (so-called cDFT$+U$) well reproduces the experimental magnetic ground state of bulk CrOX, which is not the case for the use of spin-dependent density functional (so-called sDFT$+U$). Unlike some of the previous studies, our results show that CrOX monolayers are antiferromagnetic as in the bulk. It is also consistent with our magnetic force linear response calculation of exchange couplings $J_{rm ex}$. The result of orbital-decomposed $J_{rm ex}$ calculations shows that the Cr $t_textrm{2g}$-$t_textrm{2g}$ component mainly contributes to the antiferromagnetic order in both bulk and monolayer. Our result and analysis show that taking the correct Hunds physics into account is of key importance to construct the magnetic phase diagram and to describe the electronic structure.
Density-functional calculations of lattice dynamics and high-resolution synchrotron powder diffraction uncover antiferroelectric distortion in the kagome francisite Cu$_3$Bi(SeO$_3$)$_2$O$_2$Cl below 115K. Its Br-containing analogue is stable in the
room-temperature crystal structure down to at least 10K, although the Br compound is on the verge of a similar antiferroelectric instability and reveals local displacements of Cu and Br atoms. The I-containing compound is stable in its room-temperature structure according to density-functional calculations. We show that the distortion involves cooperative displacements of Cu and Cl atoms, and originates from the optimization of interatomic distances for weakly bonded halogen atoms. The distortion introduces a tangible deformation of the kagome spin lattice and may be responsible for the reduced net magnetization of the Cl compound compared to the Br one. The polar structure of Cu$_3$Bi(SeO$_3$)$_2$O$_2$Cl is only slightly higher in energy than the non-polar antiferroelectric structure, but no convincing evidence of its formation could be obtained.
Quantum Spin Hall (QSH) insulators with a large topologically nontrivial bulk gap are crucial for future applications of the QSH effect. Among these, group III-V monolayers and their halides with chair structure (regular hexagonal framework, RHF) wer
e widely studied. Using first-principles calculations, we propose a new structure model for the functionalized group III-V monolayers, which consist of rectangular GaBi-X2 (X=I, Br, Cl) monolayers with a distorted hexagonal framework (DHF). These structures have a much lower energy than the GaBi-X2 monolayers with chair structure. Remarkably, the DHF GaBi-X2 monolayers are all QSH insulators, which exhibit sizeable nontrivial band gaps ranging from 0.17 eV to 0.39 eV. Those band gaps can be widely tuned by applying different spin-orbit coupling (SOC) strengths, resulting in a distorted Dirac cone.
(BEDT-TFF)$_2$I$_3$ charge transfer salts are reported to show superconductivity and pressure induced quasi two-dimensional Dirac cones at the Fermi level. By performing state of the art ab initio calculations in the framework of density functional t
heory, we investigate the structural and electronic properties of the three structural phases $alpha$, $beta$ and $kappa$. edit{We furthermore report about the irreducible representations of the corresponding electronic band structures, symmetry of their crystal structure, and discuss the origin of band crossings. Additionally, we discuss the chemically induced strain in $kappa$-(BEDT-TTF)$_2$I$_3$ achieved by replacing the Iodine layer with other Halogens: Fluorine, Bromine and Chlorine. In the case of $kappa$-(BEDT-TTF)$_2$F$_3$, we identify topologically protected crossings within the band structure. These crossings are forced to occur due to the non-symmorphic nature of the crystal.} The calculated electronic structures presented here are added to the organic materials database (OMDB).
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
