Recently, VIB-group layered transition metal dichalcogenides (TMDs), MX 2 (M = Mo, W; X = S, Se, Te), attracted extensive attention due to rich physiochemical properties, ranging from catalysis, [1][2][3] topological states, [4][5][6][7][8][9][10][11][12][13][14][15][16] valley polarization, [17][18][19][20][21][22] even to superconductivity. [23][24][25][26][27][28] These multiple electronic properties essentially originate from varied crystal structures of TMD materials. The typical crystal structure in TMD materials is the 2H-type structure with [X-M-X] atoms in ABA stacking in each monolayer (Figure S1a, Supporting Information). Usually, 2H MX 2 materials are semiconducting, such as, 2H MoS 2 , where the valley polarization was widely studied. [17][18][19] Also, Ising superconductivity was observed when the TMD materials are reduced down to a few or even oneRecently the metastable 1T′-type VIB-group transition metal dichalcogenides (TMDs) have attracted extensive attention due to their rich and intriguing physical properties, including superconductivity, valleytronics physics, and topological physics. Here, a new layered WS 2 dubbed "2M" WS 2 , is constructed from 1T′ WS 2 monolayers, is synthesized. Its phase is defined as 2M based on the number of layers in each unit cell and the subordinate crystallographic system. Intrinsic superconductivity is observed in 2M WS 2 with a transition temperature T c of 8.8 K, which is the highest among TMDs not subject to any fine-tuning process. Furthermore, the electronic structure of 2M WS 2 is found by Shubnikov-de Haas oscillations and first-principles calculations to have a strong anisotropy. In addition, topological surface states with a single Dirac cone, protected by topological invariant Z 2 , are predicted through first-principles calculations. These findings reveal that the new 2M WS 2 might be an interesting topological superconductor candidate from the VIB-group transition metal dichalcogenides.

The electronic structure of p-type semiconducting Sr 2 Cu 2 ZnO 2 S 2 (SCZOS) was examined experimentally and theoretically. The band gap of SCZOS estimated by the optical absorption of its thin film was 2.7 eV, which is relatively large in chalcogenide semiconductors. Normal and inverse photoemission spectra were measured to observe the valence band or conduction band structure of this material. The observed band structure revealed that the Fermi level of SCZOS was located at the top of the valence band, and the bottom of the conduction band was approximately 2.5 eV above the Fermi level. These results demonstrate the wide-gap and p-type semiconducting nature of SCZOS. Comparison of the photoemission spectra with the density of states calculated by the tight-binding method led to the conclusion that the top of the valence band is mainly composed of a hybridized (Cu 3d)-(S 3p) band, and the bottom of the conduction band primarily consists of a dispersed Zn 4s band.

Despite the fact that 1111-type iron arsenides hold the record transition temperature of ironbased superconductors, their electronic structures have not been studied much because of the lack of high-quality single crystals. In this study, we compehensively determine the Fermi surface in the antiferromagnetic state of CaFeAsF, a 1111 iron-arsenide parent compound, by performing quantum oscillation measurements and band-structure calculations. The determined Fermi surface consists of a symmetry-related pair of Dirac electron cylinders and a normal hole cylinder. From analyses of quantum-oscillation phases, we demonstrate that the electron cylinders carry a nontrivial Berry phase π. The carrier density is of the order of 10 −3 per Fe. This unusual metallic state with the extremely small carrier density is a consequence of the previously discussed topological feature of the band structure which prevents the antiferromagnetic gap from being a full gap. We also report a nearly linear-in-B magnetoresistance and an anomalous resistivity increase above about 30 T for B c, the latter of which is likely related to the quantum limit of the electron orbit. Intriguingly, the electrical resistivity exhibits a nonmetallic temperature dependence in the paramagnetic tetragonal phase (T > 118 K), which may suggest an incoherent state. Our study provides a detailed knowledge of the Fermi surface in the antiferromagnetic state of 1111 parent compounds and moreover opens up a new possibility to explore Dirac-fermion physics in those compounds.

Ferroic materials, such as ferromagnetic or ferroelectric materials, have been utilized as recording media for memory devices. A recent trend for downsizing, however, requires an alternative, because ferroic orders tend to become unstable for miniaturization. The domain wall nanoelectronics is a new developing direction for next-generation devices, in which atomic domain walls, rather than conventional, large domains themselves, are the active elements. Here we show that atomically thin magnetic domain walls generated in the antiferromagnetic insulator Cd2Os2O7 carry unusual ferromagnetic moments perpendicular to the wall as well as electron conductivity: the ferromagnetic moments are easily polarized even by a tiny field of 1 mT at high temperature, while, once cooled down, they are surprisingly robust even in an inverse magnetic field of 7 T. Thus, the magnetic domain walls could serve as a new-type of microscopic, switchable and electrically readable magnetic medium which is potentially important for future applications in the domain wall nanoelectronics.

In this study, we succeeded in synthesizing new antiperovskite phosphides MPd 3 P (M = Ca, Sr, Ba) and discovered the appearance of a superconducting phase (0.17 ≤ x ≤ 0.55) in a solid solution (Ca 1-x Sr x )Pd 3 P. Three perovskite-related crystal structures were identified in (Ca 1-x Sr x )Pd 3 P and a phase diagram was built on the basis of experimental results. The first phase transition from centrosymmetric (Pnma) to non-centrosymmetric orthorhombic (Aba2) occurred in CaPd 3 P near room temperature. The phase transition temperature decreased as Ca 2+ was replaced with a largersized isovalent Sr 2+ . Bulk superconductivity at a critical temperature (T c ) of approximately 3.5 K was observed in a range of x = 0.17-0.55; this was associated with the centrosymmetric orthorhombic phase. Thereafter, a non-centrosymmetric tetragonal phase (I4 1 md) remained stable for 0.6 ≤ x ≤ 1.0, and superconductivity was significantly suppressed as samples with x = 0.75 and 1.0 showed T c values as low as 0.32 K and 57 mK, respectively. For further substitution with a larger-sized isovalent Ba 2+ , namely (Sr 1-y Ba y )Pd 3 P, the tetragonal phase continued throughout the composition range. BaPd 3 P no longer showed superconductivity down to 20 mK. Since the inversion symmetry of structure and superconductivity can be precisely controlled in (Ca 1x Sr x )Pd 3 P, this material may offer a unique opportunity to study the relationship between inversion symmetry and superconductivity.