Large Variation of Dirac Semimetal State in Perovskite CaIrO_{3} with Pressure-Tuning of Electron Correlation

The impact of electron correlation on the Dirac semimetal state is investigated for perovskite CaIrO_{3} in terms of the magnetotransport properties under varying pressures. The reduction of electron correlation with a pressure of 1 GPa enhances the Fermi velocity as much as 40%, but it reduces the mobility by an order of magnitude by detuning the Dirac node from the Fermi energy. Moreover, the giant magnetoresistance at the quantum limit due to the one-dimensional confinement of Dirac electrons is critically suppressed under pressure. These results indicate that the electron correlation is a crucial knob for controlling the transport of a correlated Dirac semimetal.

Strong-correlation induced high-mobility electrons in Dirac semimetal of perovskite oxide

Electrons in conventional metals become less mobile under the influence of electron correlation. Contrary to this empirical knowledge, we report here that electrons with the highest mobility ever found in known bulk oxide semiconductors emerge in the strong-correlation regime of the Dirac semimetal of perovskite CaIrO₃. The transport measurements reveal that the high mobility exceeding 60,000 cm²V⁻¹s⁻¹ originates from the proximity of the Fermi energy to the Dirac node (ΔE < 10 meV). The calculation based on the density functional theory and the dynamical mean field theory reveals that the energy difference becomes smaller as the system approaches the Mott transition, highlighting a crucial role of correlation effects cooperating with the spin-orbit coupling. The correlation-induced self-tuning of Dirac node enables the quantum limit at a modest magnetic field with a giant magnetoresistance, thus providing an ideal platform to study the novel phenomena of correlated Dirac electron.

Electron correlation normally makes electrons less mobile, but it is still not clear when correlation becomes very strong in Dirac semimetals. Here, Fujioka et al. report a very high electron mobility exceeding 60,000 cm²V⁻¹s⁻¹ in correlated Dirac semimetal of perovskite CaIrO3, due to the enhanced electron correlation nearby the Mott transition.

Superconductivity at the Polar-Nonpolar Phase Boundary of SnP with an Unusual Valence State

Structural, magnetic, and electrical characterizations reveal that SnP with an unusual valence state (nominally Sn^{3+}) undergoes a ferroelectriclike structural transition from a simple NaCl-type structure to a polar tetragonal structure at approximately 250 K at ambient pressure. First-principles calculations indicate that the experimentally observed tetragonal distortion enhances the charge transfer from Sn to P, thereby making the polar tetragonal phase energetically more stable than the nonpolar cubic phase. Hydrostatic pressure is found to promptly suppress the structural phase transition in SnP, leading to the emergence of bulk superconductivity in a phase-competitive manner. These findings suggest that control of ferroelectriclike instability in a metal can be a promising way for creating novel superconductors.

Polar metal phase stabilized in strained La-doped BaTiO3films

Ferroelectric polarization and metallic conduction are two seemingly irreconcilable properties that cannot normally coexist in a single system, as the latter tends to screen the former. Polar metals, however, defy this rule and have thus attracted considerable attention as a new class of ferroelectrics exhibiting novel properties. Here, we fabricate a new polar metal film based on the typical ferroelectric material BaTiO₃by combining chemical doping and epitaxial strain induced by a substrate. The temperature dependences of the c-axis lattice constant and the second harmonic generation intensity of La-doped BaTiO₃films indicate the existence of polar transitions. In addition, through La doping, films become metallic at the polar phase, and metallicity enhancement at the polar state occurs in low-La-doped films. This intriguing behaviour is effectively explained by our first-principles calculations. Our demonstration suggests that the carrier doping to ferroelectric material with epitaxial strain serves as a new way to explore polar metals.

Superconductivity in a chiral nanotube

Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity—unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures.

Chirality affects many properties of materials, but how it affects superconductivity remains unclear. Here, Qin et al. report nonreciprocal supercurrent flows in individual nanotubes of WS₂ via ionic gating, evidencing chiral superconducting transport.

Ambipolar organic field-effect transistors based on solution-processed single crystal microwires of a quinoidal oligothiophene derivative

A simple and versatile solution-processing method based on molecular self-assembly is used to fabricate organic single crystal microwires of a low bandgap quinoidal oligothiophene derivative. Individual single crystal microwire transistors present well-balanced ambipolar behaviour with hole and electron mobilities as high as 0.4 and 0.5 cm(2) V(-1) s(-1), respectively.

Photophysical, amplified spontaneous emission and charge transport properties of oligofluorene derivatives in thin films

We investigate the charge transport, photophysical and amplified spontaneous emission properties of a series of monodisperse solution-processable oligofluorenes functionalized with hexyl chains at the C9 position of each fluorene unit.

A-type antiferro-orbital ordering with I4(1)/a symmetry and geometrical frustration in the spinel vanadate MgV2O4

We conduct a detailed structural analysis of the S=1 pyrochlore antiferromagnet MgV2O4, which exhibits an antiferromagnetic ordering marginally at TN=40  K, triggered by a structural transition from cubic to tetragonal symmetry at TS=62  K, using high resolution synchrotron x-ray diffraction and convergent beam electron diffraction. We reveal that the tetragonal phase below TS has the symmetry of I4(1)/a and that the distortion pattern of VO6 octahedra is consistent with A-type antiferro-orbital ordering with alternating stacking of layers with yz/xy orbital chains and zx/xy orbital chains along the tetragonal c axis. This implies that an anisotropic coupling of V moments produced by the orbital ordering below TS primarily brings about the antiferromagnetic ordering.

Displacement-type ferroelectricity with off-center magnetic ions in perovskite Sr(1-x)Ba(x)MnO3

We report a ferroelectric transition driven by the off-centering of magnetic Mn(4+) ions in antiferromagnetic Mott insulators Sr(1-x)Ba(x)MnO(3) with a perovskite structure. As x increases, the perovskite lattice shows the typical soft-mode dynamics, as revealed by the momentum-resolved inelastic x-ray scattering and far-infrared spectroscopy, and the ferroelectricity shows up for x ≥ 0.45. The observed polarization is comparable to that for a prototypical ferroelectric BaTiO(3). We further demonstrate that the magnetic order suppresses the ferroelectric lattice dilation by ∼70% and increases the soft-phonon energy by ∼50%, indicating the largest magnetoelectric effects yet attained.

Anomalous metallic state in the vicinity of metal to valence-bond solid insulator transition in LiVS2

We investigate LiVS2 and LiVSe2 with a triangular lattice as itinerant analogues of LiVO2 known for the formation of a valence-bond solid (VBS) state out of an S=1 frustrated magnet. LiVS2, which is located at the border between a metal and a correlated insulator, shows a first order transition from a paramagnetic metal to a VBS insulator at Tc approximately 305 K upon cooling. The presence of a VBS state in the close vicinity of insulator-metal transition may suggest the importance of itinerancy in the formation of a VBS state. We argue that the high temperature metallic phase of LiVS2 has a pseudogap, likely originating from the VBS fluctuation. LiVSe2 was found to be a paramagnetic metal down to 2 K.

Two-component molecular crystals from N-heteroaromatics and nitrobenzoic acids

Five two-component molecular crystals, benzimidazolium 3-nitrobenzoate, C(7)H(7)N(2)(+).C(7)H(4)NO(4)(-), (I), benzimidazolium 4-nitrobenzoate, C(7)H(7)N(2)(+).C(7)H(4)NO(4)(-), (II), 1H-benzotriazole-3-nitrobenzoic acid (1/1), C(6)H(5)N(3).C(7)H(5)NO(4), (III), imidazolium 3-nitrobenzoate, C(3)H(5)N(2)(+).C(7)H(4)NO(4)(-), (IV), and imidazolium 4-nitrobenzoate, C(3)H(5)N(2)(+).C(7)H(4)NO(4)(-), (V), were prepared with the aim of making chiral crystals. Only (I) crystallizes in a chiral space group. The molecules of (I) and (II) are linked by hydrogen bonds to form 2(1) spiral chains. In (III), (IV) and (V), macrocyclic structures are formed from two acid and two base components, by an alternate arrangement of the acid and base moieties.

Radical-copper wheels: structure and magnetism of hexanuclear hybrid arrays

Complexation of copper(II) bromide and chloride with 4-pyrimidinyl nitronyl nitroxide (4PMNN) as a bridging ligand gave discrete hexanuclear complexes carrying 12 spins, [CuX(2).(4PMNN)](6) [X = Br (1), Cl (2)], which crystallize in a trigonal space group. The crystallographic parameters are C(11)H(15)Br(2)CuN(4)O(2).0.3H(2)O, a = 28.172(2), c = 12.590(2) A, V = 8653(2) A(3), and Z = 18 for 1, and C(11)H(15)Cl(2)CuN(4)O(2).0.3H(2)O, a = 28.261(2), c = 12.378(1) A, and Z = 18 for 2. The hexanuclear arrays construct a perfect column perpendicular to the molecular plane. The diameter of the resultant honeycomblike channel is ca. 11.5 A defined by the interatomic distance of two opposing copper ions. Their magnetic behavior is interpreted as the simultaneous presence of ferro and antiferromagnetic couplings. The ferromagnetic couplings are attributed to the interactions between a copper spin and the axially coordinated nitronyl nitroxide spin and between nitronyl nitroxide groups through van der Waals contacts. The antiferromagnetic coupling is due to the interaction between copper ions across the pyrimidine bridges.

Four polymorphs of a cobaloxime complex with different solid-state photoisomerization rates

The complex (2-cyanoethyl)bis(dimethylglyoximato)(triphenylphosphine)cobalt(III), [Co(C4H7N2O2)2(C3H4N){P(C6H5)3}], when it was crystallized rapidly from an aqueous methanol solution, has four crystal forms, three of which were obtained separately from different solvents in large amounts. The crystal structures of the four forms were determined by X-rays. The molecular structures in the four forms have different conformations around the Co—C and Co—P bonds. The packing energy calculation indicated that the four forms have approximately the same energy. The 2-cyanoethyl group of this complex was isomerized to the 1-cyanoethyl group when the powdered sample of the complex was irradiated with a xenon lamp. For three crystal forms prepared separately, the solid-state photoisomerization rates were measured from the change in the IR spectra, assuming first-order kinetics. A quantitative relationship between the rate constant and the size of the reaction cavity for the 2-cyanoethyl group has been obtained for the three crystal forms.