transition metal dichalcogenides (TMDCs) have been extensively studied. Among them, vanadium dichalcogenides, a unique metallic family of the TMDCs, have been considered as potential room temperature ferromagnetic materials at the monolayer scale. However, further progress has been hampered by the difficulties growing monolayer and the challenges making high-quality single crystalline VSe 2 , free from artificial factors. Here, we report high-quality octahedral 1T-VSe 2 single crystals grown by chemical vapor transport. Spectroscopic analyses identified that as-grown VSe 2 crystals were a single phase of VSe 2 and highly oriented along the (00l) plane. High-resolution scanning transmission electron microscopy verified that as-grown VSe 2 crystals not only had single crystalline nature, the octahedral 1T phase, and AAA stacking order in atomistic real space, but also supported valuable lattice information that differed from the predicted values of the previous calculation model. Mechanical exfoliation allowed our VSe 2 crystals to turn into largesized VSe 2 flakes with various thicknesses. With in-depth structural analyses, our findings provide insight into further research of the fundamental calculation model and the crystallographic tailoring for intrinsic room-temperature 2D ferromagnetic materials.

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An antiferromagnetic topological insulator has been predicted to be preserved by breaking both timereversal symmetry and primitive lattice translational symmetry. However, the topological surface state has often been observed to disappear in an antiferromagnetic phase because the doped magnetic impurity acts as an extrinsic defect. in this study, we report the experimental signature of topological surface states coexisting with antiferromagnetic order in Sm-doped Bi 2 te 3. We fabricate single crystals of Sm x Bi 2−x te 3 with x = 0.004, 0.010, and 0.025, where the Curie-Weiss law is satisfied at low temperatures but is violated at high temperatures due to the influence of the high energy states of J multiplets of Sm. for x = 0.025, e xotic physical properties are observed, such as the antiferromagnetic phase with the néel temperature T n = 3.3 K, multi-band Hall effect with two conduction channel, and anisotropic Shubnikov-de Haas oscillations. in the antiferromagnetic phase, we detect the signature of nontrivial topological surface states with surface electron density n s = 7.9 × 10 11 cm −2 and its high mobility μ s = 2,200 cm 2 /Vs, compared to n b = 2.0 × 10 19 cm −3 and μ b = 2.3 cm 2 /Vs for bulk electrons. these observations suggest that Sm x Bi 2−x te 3 is a candidate creating the new stage for the potential application of topological antiferromagnetic spintronics.

With the emergence of Dirac fermion physics in the field of condensed matter, magnetic quantum oscillations (MQOs) have been used to discern the topology of orbits in Dirac materials. However, many previous researchers have relied on the single-orbit Lifshitz–Kosevich (LK) formula, which overlooks the significant effect of degenerate orbits on MQOs. Since the single-orbit LK formula is valid for massless Dirac semimetals with small cyclotron masses, it is imperative to generalize the method applicable to a wide range of Dirac semimetals, whether massless or massive. This report demonstrates how spin-degenerate orbits affect the phases in MQOs of three-dimensional massive Dirac semimetal, NbSb2. With varying the direction of the magnetic field, an abrupt π phase shift is observed due to the interference between the spin-degenerate orbits. We investigate the effect of cyclotron mass on the π phase shift and verify its close relation to the phase from the Zeeman coupling. We find that the π phase shift occurs when the cyclotron mass is half of the electron mass, indicating the effective spin gyromagnetic ratio as gs = 2. Our approach is not only useful for analyzing MQOs of massless Dirac semimetals with a small cyclotron mass but also can be used for MQOs in massive Dirac materials with degenerate orbits, especially in topological materials with a sufficiently large cyclotron mass. Furthermore, this method provides a useful way to estimate the precise gs value of the material.

Antiferromagnetic topological insulators have attracted great attention in the condensed matter physics owing to the fundamental interest in exotic quantum states and topological antiferromagnetic spintronics. Starting with the typical topological insulator of Bi2Te3, we introduced the magnetic order by substituting Gd at the Bi site and tuned the Fermi level by substituting Se at the Te site. That is, we prepared single crystals of Gd xBi2− xTe3− ySe y with various x (= 0.02 and 0.06) and y (= 0.1, 0.2, 0.5, 0.7, 1.0, and 1.5). The magnetic data revealed an antiferromagnetic order for x = 0.06, and the transport data manifested the charge neutral point at y = 0.7. Combining all these results together, the material with x = 0.06 and y = 0.7 is characterized as an antiferromagnetic topological insulator, where we observed exotic magnetotransport properties such as weak antilocalization and negative longitudinal magnetoresistance that are frequently analyzed as chiral anomalies in Weyl materials.