Manipulating Dirac States in BaNiS2 by Surface Charge Doping.

In the Dirac semimetal BaNiS2, the Dirac nodes are located along the Γ-M symmetry line of the Brillouin zone, instead of being pinned at fixed high-symmetry points. We take advantage of this peculiar feature to demonstrate the possibility of moving the Dirac bands along the Γ-M symmetry line in reciprocal space by varying the concentration of K atoms adsorbed onto the surface of cleaved BaNiS2 single crystals. By means of first-principles calculations, we give a full account of this observation by considering the effect of the electrons donated by the K atom on the charge transfer gap, which establishes a promising tool for engineering Dirac states at surfaces, interfaces, and heterostructures.

Residential Greenspace Is Associated with Lower Levels of Depressive and Burnout Symptoms, and Higher Levels of Life Satisfaction: A Nationwide Population-Based Study in Sweden.

Population-based studies of individual-level residential greenspace and mental health outcomes are still limited. Thus, the present study investigates greenspace-mental health associations-including depressive symptoms, burnout symptoms, and life satisfaction-in a population-based sample of adults, the Swedish Longitudinal Occupational Survey of Health, in 2016 (n = 14,641). High-resolution land cover of greenspace and green-blue-space was assessed at 50, 100, 300 and 500 m buffers around residential addresses. Higher residential greenspace and green-blue-space were associated with lower levels of depressive and burnout symptoms among non-working individuals and with higher life satisfaction in the whole study population, after controlling for age, sex, individual income, and neighborhood socioeconomics. The immediate residential-surrounding environment (50 m) consistently showed the strongest associations with the outcomes. Having a partner was associated with better mental health outcomes and with having more residential greenspace, and adjusting for this rendered greenspace-health associations mostly statistically non-significant. In conclusion, higher levels of greenspace and green-blue-space in the immediate residential-surrounding environment were associated with better mental health outcomes in the present study, which contributes additional nuances to prior studies. The importance of residential greenspace for public health, urban planning, and development is discussed.

Thermoelectric materials taking advantage of spin entropy: lessons from chalcogenides and oxides.

The interplay between charges and spins may influence the dynamics of the carriers and determine their thermoelectric properties. In that respect, magneto-thermoelectric power MTEP, i.e. the measurements of the Seebeck coefficient S under the application of an external magnetic field, is a powerful technique to reveal the role of magnetic moments on S. This is illustrated by different transition metal chalcogenides: CuCrTiS4 and CuMnTiS4 magnetic thiospinels, which are compared with magnetic oxides, Curie-Weiss (CW) paramagnetic misfit cobaltites, ruthenates, either ferromagnetic perovskite or Pauli paramagnet quadruple perovskites, and CuGa1-x Mn x Te2 chalcopyrite telluride and Bi1.99Cr0.01Te3 in which diluted magnetism is induced by 3%-Mn and 1%-Cr substitution, respectively. In the case of a ferromagnet (below TC) and CW paramagnetic materials, the increase of magnetization at low T when a magnetic field is applied is accompanied by a decrease of the entropy of the carriers and hence S decreases. This is consistent with the lack of MTEP in the Pauli paramagnetic quadruple perovskites. Also, no significant MTEP is observed in CuGa1-x Mn x Te2 and Bi1.99Cr0.01Te3, for which Kondo-type interaction between magnetic moments and carriers prevails. In contrast, spin glass CuCrTiS4 exhibits negative MTEP like in ferromagnetic ruthenates and paramagnetic misfit cobaltites. This investigation of some chalcogenides and oxides provides key ingredients to select magnetic materials for which S benefits from spin entropy.

Moving Dirac nodes by chemical substitution.

Dirac fermions play a central role in the study of topological phases, for they can generate a variety of exotic states, such as Weyl semimetals and topological insulators. The control and manipulation of Dirac fermions constitute a fundamental step toward the realization of novel concepts of electronic devices and quantum computation. By means of Angle-Resolved Photo-Emission Spectroscopy (ARPES) experiments and ab initio simulations, here, we show that Dirac states can be effectively tuned by doping a transition metal sulfide, [Formula: see text], through Co/Ni substitution. The symmetry and chemical characteristics of this material, combined with the modification of the charge-transfer gap of [Formula: see text] across its phase diagram, lead to the formation of Dirac lines, whose position in k-space can be displaced along the [Formula: see text] symmetry direction and their form reshaped. Not only does the doping x tailor the location and shape of the Dirac bands, but it also controls the metal-insulator transition in the same compound, making [Formula: see text] a model system to functionalize Dirac materials by varying the strength of electron correlations.

Centrosymmetry Breaking and Ferroelectricity Driven by Short-Range Magnetic Order in the Quadruple Perovskite (YMn3)Mn4O12.

By means of single-crystal X-ray diffraction, we give direct crystallographic evidence of a centrosymmetry breaking below TS = 200 K, concomitant with the onset of a commensurate structural modulation in the quadruple perovskite YMn3Mn4O12. This result, which explains the anomalously large thermal coefficient of the Y3+ ion in previously reported structural models, is attributed to the small size of the Y3+ ion, which causes its underbonding within the dodecahedral coordination polyhedron. The present data are consistent with a commensurate superstructure described by an I-centered pseudo-orthorhombic cell with polar Ia symmetry and a ≈ aF√2 = 10.4352(7) Å, b ≈ 2bF = 14.6049(9) Å, c ≈ cF√2 = 10.6961(7) Å, and ß = 90.110(3)°, where aF ≈ cF ≈ 7.45 Å, bF ≈ 7.34 Å, and ß ≈ 91° are the unit cell parameters of the I2/m structure observed at room temperature. Consistent with the above polar structure, at lower temperature, T* = 70 K, we observe in polycrystalline samples an anomaly of the direct current (DC) and alternating current (AC) magnetization, concomitant with the appearance of a net electric polarization, as indicated by pyrocurrent and dielectric constant measurements. These results, complemented by electrical transport measurements, suggest a magnetic ferroelectricity driven by short-range magnetic order in YMn3Mn4O12.

High-Pressure Control of Vanadium Self-Intercalation and Enhanced Metallic Properties in 1T-V1+xS2 Single Crystals.

By means of high-pressure synthesis in the 4-6 GPa range, we report on the successful growth of high-quality 1T-V1+xS2 single crystals with controlled concentration, x = 0.09-0.17, of self-intercalated V atoms in the van der Waals gap. A systematic X-ray diffraction and energy-dispersive X-ray spectroscopy study unveils a linear decrease of x with the synthesis pressure, dx/dP = -0.042 GPa(-1), suggesting that the stoichiometric (x = 0) phase is stable above 8 GPa. Transmission electron microscopy and electrical resistivity measurements show that, for all x values studied, the system is metallic up to 400 K, with no charge-density-wave order, contrary to the x = 0 composition. This finding clarifies the controversial electronic phase diagram of the 1T-V1+xS2 system and unveils a connection between the charge-density-wave phase observed at x = 0 and the itinerant antiferromagnetic phase stable for x > 0.25.

Rashba coupling amplification by a staggered crystal field.

There has been increasing interest in materials where relativistic effects induce non-trivial electronic states with promise for spintronics applications. One example is the splitting of bands with opposite spin chirality produced by the Rashba spin-orbit coupling in asymmetric potentials. Sizable splittings have been hitherto obtained using either heavy elements, where this coupling is intrinsically strong, or large surface electric fields. Here by means of angular resolved photoemission spectroscopy and first-principles calculations, we give evidence of a large Rashba coupling of 0.25 eV Å, leading to a remarkable band splitting up to 0.15 eV with hidden spin-chiral polarization in centrosymmetric BaNiS2. This is explained by a huge staggered crystal field of 1.4 V Å(-1), produced by a gliding plane symmetry, that breaks inversion symmetry at the Ni site. This unexpected result in the absence of heavy elements demonstrates an effective mechanism of Rashba coupling amplification that may foster spin-orbit band engineering.

Neutron diffraction study of the Li-ion battery cathode Li2FeP2O7.

With a combination of magnetic susceptibility measurements and low-temperature neutron diffraction analyses, the magnetic structure of Li2FeP2O7 cathode has been solved. This pyrophosphate Li2FeP2O7 compound stabilizes into a monoclinic framework (space group P2(1)/c), having a pseudolayered structure with the constituent Li/Fe sites distributed into MO6 and MO5 building units. The magnetic susceptibility follows a Curie-Weiss behavior above 50 K. Li2FeP2O7 shows a long-range antiferromagnetic ordering at T(N) = 9 K, as characterized by the appearance of distinct additional peaks in the neutron diffraction pattern below T(N). Its magnetic reflections can be indexed with a propagation vector k = (0,0,0). The magnetic moments inside the FeO6-FeO5 clusters are ferromagnetic, whereas these clusters are antiferromagnetic along the chains. The adjacent chains are in turn ferromagnetically arranged along the a-axis. The magnetic structure of Li2FeP2O7 cathode material is described focusing on their localized spin-spin exchange. The magnetic structure and properties have been generalized for Li2FeP2O7-Li2CoP2O7 binary solid solutions.