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We conducted a high-throughput search for topological magnetic materials across 522 new, experimentally reported commensurate magnetic structures from MAGNDATA, doubling the number of available materials on the Topological Magnetic Materials database. This brings up to date the previous studies. For each material, we performed first-principles electronic calculations and diagnosed the topology as a function of the HubbardUparameter. Our high-throughput calculation led us to the prediction of 250 experimentally relevant topologically nontrivial materials, which represent 47.89% of the newly analyzed materials. We present five remarkable examples of these materials, each showcasing a different topological phase: Mn₂AlB₂(BCSID 1.508), which exhibits a nodal line semimetal to topological insulator transition as a function of SOC; CaMnSi (BCSID 0.599), a narrow gap axion insulator; UAsS (BCSID 0.594), a 5f-orbital Weyl semimetal; CsMnF₄(BCSID 0.327), a material presenting a new type of quasi-symmetry protected closed nodal surface; and FeCr₂S₄(BCSID 0.613), a symmetry-enforced semimetal with double Weyls and spin-polarized surface states. 

Abstract When two monolayer materials are stacked with a relative twist, an effective moiré translation symmetry emerges, leading to fundamentally different properties in the resulting heterostructure. As such, moiré materials have recently provided highly tunable platforms for exploring strongly correlated systems^1,2. However, previous studies have focused almost exclusively on monolayers with triangular lattices and low-energy states near the Γ (refs. ^3,4) or K (refs. ^5–9) points of the Brillouin zone (BZ). Here we introduce a new class of moiré systems based on monolayers with triangular lattices but low-energy states at the M points of the BZ. These M-point moiré materials feature three time-reversal-preserving valleys related by threefold rotational symmetry. We propose twisted bilayers of exfoliable 1T-SnSe₂and 1T-ZrS₂as realizations of this new class. Using extensive ab initio simulations, we identify twist angles that yield flat conduction bands, provide accurate continuum models, analyse their topology and charge density and explore the platform’s rich physics. Notably, the M-point moiré Hamiltonians exhibit emergent momentum-space non-symmorphic symmetries and a kagome plane-wave lattice structure. This represents, to our knowledge, the first experimentally viable realization of projective representations of crystalline space groups in a non-magnetic system. With interactions, these systems act as six-flavour Hubbard simulators with Mott physics. Moreover, the presence of a momentum-space non-symmorphic in-plane mirror symmetry renders some of the M-point moiré Hamiltonians quasi-one-dimensional in each valley, suggesting the possibility of realizing Luttinger-liquid physics. 

Abstract The discovery of topological semimetals with multifold band crossings has opened up a new and exciting frontier in the field of topological physics. These materials exhibit large Chern numbers, leading to long double Fermi arcs on their surfaces, which are protected by either crystal symmetries or topological order. The impact of these multifold crossings extends beyond surface science, as they are not constrained by the Poincar classification of quasiparticles and only need to respect the crystal symmetry of one of the 1651 magnetic space groups. Consequently, we observe the emergence of free fermionic excitations in solid-state systems that have no high-energy counterparts, protected by non-symmorphic symmetries. In this work, we review the recent theoretical and experimental progress made in the field of multifold topological semimetals. We begin with the theoretical prediction of the so-called multifold fermions and discuss the subsequent discoveries of chiral and magnetic topological semimetals. Several experiments that have realized chiral semimetals in spectroscopic measurements are described, and we discuss the future prospects of this field. These exciting developments have the potential to deepen our understanding of the fundamental properties of quantum matter and inspire new technological applications in the future. 

Spin-forbidden ( $\mathrm{\Delta }S\ne 0$) multiplet excitations and their coupling to magnetic properties are of increasing importance for magneto-optical studies of correlated materials. Nonetheless, the mechanisms for optically brightening these transitions and their generality remain poorly understood. Here, we report magnetic circular dichroism (MCD) spectroscopy on the van der Waals ferromagnet (FM) ${\mathrm{CrI}}_3$. Previously unreported spin-forbidden ( $\mathrm{\Delta }S=1$) ${{}^{4}A}_{2\mathrm{g}}\to {{}^{2}E}_{\mathrm{g}}/{{}^{2}T}_{1\mathrm{g}}$ ${\mathrm{Cr}}^{3+}$ $dd$excitations are observed near the ligand-to-metal charge-transfer excitation threshold. The assignment of these excitations and their ${\mathrm{Cr}}^{3+}$multiplet character is established through complementary Cr $L_3$-edge resonant inelastic x-ray scattering measurements along with charge-transfer multiplet calculations and chemical trends in the chromium trihalide series ( $\mathrm{Cr}{X}_3$, $X=$Cl, Br, I). We utilize the high sensitivity of MCD spectroscopy to study the thickness-dependent optical response. The spin-forbidden excitations remain robust down to the monolayer limit, and we observe a significant magnetic-field dependence of the MCD spectrum across the antiferromagnetic-to-FM transition in few-layer samples. We preliminarily attribute this behavior to changes in the metal-ligand covalency with magnetic state. Our results clarify the magneto-optical response of ${\mathrm{CrI}}_3$and identify covalency as a central mechanism for the brightening and field tunability of spin-forbidden multiplet excitations. 

Abstract Weyl semimetals exhibit exotic magnetotransport phenomena such as the chiral anomaly and surface-to-bulk quantum oscillations (Weyl orbits) due to chiral bulk states and topologically protected surface states. Here we report a unique transport property in crystals of the ferromagnetic nodal-line Weyl semimetal Co₂MnGa that have been polished to micron thicknesses using a focused ion beam. These thin crystals exhibit a large planar resistance anisotropy (10 × ) with axes that rotate by 90 degrees between opposite faces of the crystal. We use symmetry arguments and electrostatic simulations to show that the observed anisotropy resembles that of an isotropic conductor with surface states that are impeded from hybridization with bulk states. The origin of these states awaits further experiments that can correlate the surface bands with the observed 90° twist.