Role of Strain on Electronic and Mechanical Response of Semiconducting Transition-Metal Dichalcogenide Monolayers: an ab-initio study

We characterize the electronic structure and elasticity of monolayer transition-metal dichalcogenides MX2 (M=Mo, W, Sn, Hf and X=S, Se, Te) with 2H and 1T structures using fully relativistic first principles calculations based on density functional theory. We focus on the role of strain on the band structure and band alignment across the series 2D materials. We find that strain has a significant effect on the band gap; a biaxial strain of 1% decreases the band gap in the 2H structures, by as a much 0.2 eV in MoS2 and WS2, while increasing it for the 1T materials. These results indicate that strain is a powerful avenue to modulate their properties; for example, strain enables the formation of, otherwise impossible, broken gap heterostructures within the 2H class. These calculations provide insight and quantitative information for the rational development of heterostructures based on these class of materials accounting for the effect of strain.Comment: 16 pages, 4 figures, 1 table, supplementary materia

Shape evolution in Yttrium and Niobium neutron-rich isotopes

The isotopic evolution of the ground-state nuclear shapes and the systematics of one-quasiproton configurations are studied in neutron-rich odd-A Yttrium and Niobium isotopes. We use a selfconsistent Hartree-Fock-Bogoliubov formalism based on the Gogny energy density functional with two parametrizations, D1S and D1M. The equal filling approximation is used to describe odd-A nuclei preserving both axial and time reversal symmetries. Shape-transition signatures are identified in the N=60 isotopes in both charge radii and spin-parities of the ground states. These signatures are a common characteristic for nuclei in the whole mass region. The nuclear deformation and shape coexistence inherent to this mass region are shown to play a relevant role in the understanding of the spectroscopic features of the ground and low-lying one-quasiproton states. Finally, a global picture of the neutron-rich A=100 mass region from Krypton up to Molybdenum isotopes is illustrated with the systematics of the nuclear charge radii isotopic shifts.Comment: 21 pages, 14 figures. To be published in Phys. Rev.

Systematics of one-quasiparticle configurations in neutron-rich Sr, Zr, and Mo odd isotopes with the Gogny energy density functional

The systematics of one-quasiparticle configurations in neutron-rich Sr, Zr, and Mo odd isotopes is studied within the Hartree-Fock-Bogoliubov plus Equal Filling Approximation method preserving both axial and time reversal symmetries. Calculations based on the Gogny energy density functional with both the standard D1S parametrization and the new D1M incarnation of this functional are included in our analysis. The nuclear deformation and shape coexistence inherent to this mass region are shown to play a relevant role in the understanding of the spectroscopic features of the ground and low-lying one-quasineutron states.Comment: 11 page

Signatures of shape transition in odd-A neutron-rich Rubidium isotopes

The isotopic evolution of the ground-state nuclear shapes and the systematics of one-quasiproton configurations are studied in odd-A Rubidium isotopes. We use a selfconsistent Hartree-Fock-Bogoliubov formalism based on the Gogny energy density functional with two parametrizations, D1S and D1M, and implemented with the equal filling approximation. We find clear signatures of a sharp shape transition at N=60 in both charge radii and spin-parity of the ground states, which are robust, consistent to each other, and in agreement with experiment. We point out that the combined analysis of these two observables could be used to predict unambiguously new regions where shape transitions might develop.Comment: 6 pages, 7 figures. To appear in Phys. Rev. C (Rapid Communications

Microscopic description of quadrupole-octupole coupling in Sm and Gd isotopes with the Gogny Energy Density Functional

The interplay between the collective dynamics of the quadrupole and octupole deformation degree of freedom is discussed in a series of Sm and Gd isotopes both at the mean field level and beyond, including parity symmetry restoration and configuration mixing. Physical properties like negative parity excitation energies, E1 and E3 transition probabilities are discussed and compared to experimental data. Other relevant intrinsic quantities like dipole moments, ground state quadrupole moments or correlation energies associated to symmetry restoration and configuration mixing are discussed. For the considered isotopes, the quadrupole-octupole coupling is found to be weak and most of the properties of negative parity states can be described in terms of the octupole degree of freedom alone.Comment: 31 pages, 11 figure

Gravitational cooling of self-gravitating Bose-Condensates

Equilibrium configurations for a self-gravitating scalar field with self-interaction are constructed. The corresponding Schr\"odinger-Poisson (SP) system is solved using finite differences assuming spherical symmetry. It is shown that equilibrium configurations of the SP system are late-time attractor solutions for initially quite arbitrary density profiles, which relax and virialize through the emission of scalar field bursts; a process dubbed gravitational cooling. Among other potential applications, these results indicate that scalar field dark matter models (in its different flavors) tolerate the introduction of a self-interaction term in the SP equations. This study can be useful in exploring models in which dark matter in galaxies is not point-like.Comment: 10 aastex pages, 12 eps figures. Accepted for publication in Ap

Tracing the magnetic field of IRDC G028.23-00.19 using NIR polarimetry

The importance of the magnetic (B) field in the formation of infrared dark clouds (IRDCs) and massive stars is an ongoing topic of investigation. We studied the plane-of-sky B field for one IRDC, G028.23-00.19, to understand the interaction between the field and the cloud. We used near-IR background starlight polarimetry to probe the B field and performed several observational tests to assess the field importance. The polarimetric data, taken with the Mimir instrument, consisted of H-band and K-band observations, totaling 17,160 stellar measurements. We traced the plane-of-sky B-field morphology with respect to the sky-projected cloud elongation. We also found the relationship between the estimated B-field strength and gas volume density, and we computed estimates of the normalized mass-to-magnetic flux ratio. The B-field orientation with respect to the cloud did not show a preferred alignment, but it did exhibit a large-scale pattern. The plane-of-sky B-field strengths ranged from 10 to 165 μG, and the B-field strength dependence on density followed a power law with an index consistent with 2/3. The mass-to-magnetic flux ratio also increased as a function of density. The relative orientations and relationship between the B field and density imply that the B field was not dynamically important in the formation of the IRDC. The increase in mass-to-flux ratio as a function of density, though, indicates a dynamically important B field. Therefore, it is unclear whether the B field influenced the formation of G28.23. However, it is likely that the presence of the IRDC changed the local B-field morphology.We thank J. Montgomery, T. Hogge, and I. Stephens for constructive discussions on the analysis. We are grateful to R. Crutcher for permission to include his Zeeman data. This research was conducted in part using the Mimir instrument, jointly developed at Boston University and Lowell Observatory and supported by NASA, NSF, and the W.M. Keck Foundation. This research made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology (Caltech), under contract with NASA. This publication made use of data products from the Two Micron All Sky Survey, which was a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/Caltech, funded by NASA and NSF. This work is based in part on data obtained as part of the UKIRT Infrared Deep Sky Survey. The ATLAS-GAL project is a collaboration between the Max-PlanckGesellschaft, the European Southern Observatory (ESO), and the Universidad de Chile. It includes projects E-181.C-0885, E-078.F-9040(A), M-079.C-9501(A), M-081.C-9501(A), and Chilean data. This publication makes use of molecular line data from the Boston University-FCRAO Galactic Ring Survey (GRS). The GRS is a joint project of Boston University and Five College Radio Astronomy Observatory, funded by the National Science Foundation under grants AST-9800334, 0098562, 0100793, 0228993, and. 0507657. A.E.G. acknowledges support from FONDECYT 3150570. This work was supported under NSF grants AST 09-07790 and 14-12269 and NASA grant NNX15AE51G to Boston University. We thank the anonymous referee for valuable feedback, which improved the quality of this work. (NASA; NSF; W.M. Keck Foundation; E-181.C-0885 - Max-Planck-Gesellschaft; E-078.F-9040(A) - Max-Planck-Gesellschaft; M-079.C-9501(A) - Max-Planck-Gesellschaft; M-081.C-9501(A) - Max-Planck-Gesellschaft; E-181.C-0885 - European Southern Observatory (ESO); E-078.F-9040(A) - European Southern Observatory (ESO); M-079.C-9501(A) - European Southern Observatory (ESO); M-081.C-9501(A) - European Southern Observatory (ESO); E-181.C-0885 - Universidad de Chile; E-078.F-9040(A) - Universidad de Chile; M-079.C-9501(A) - Universidad de Chile; M-081.C-9501(A) - Universidad de Chile; AST-9800334 - National Science Foundation; 0098562 - National Science Foundation; 0100793 - National Science Foundation; 0228993 - National Science Foundation; 0507657 - National Science Foundation; 3150570 - FONDECYT; AST 09-07790 - NSF; 14-12269 - NSF; NNX15AE51G - NASA

Modelling the rotational curves of spiral galaxies with a scalar field

In a previous work (Mbelek 2001), we modelled the rotation curves (RC) of spiral galaxies by including in the equation of motion of the stars the dynamical terms from an external real self-interacting scalar field, $\psi$, minimally coupled to gravity and which respects the equivalence principle in the weak fields and low velocity approximation. This model appeared to have three free parameters : the turnover radius, $r_{0}$, the maximum tangential velocity, $v_{\theta max} = v_{\theta}(r_{0})$, plus a strictly positive integer, $n$. Here, we propose a new improved version where the coupling of the $\psi$-field to dark matter is emphasized at the expense of its self-interaction. This reformulation presents the very advantageous possibility that the same potential is used for all galaxies. Using at the same time a quasi-isothermal dark matter density and the scalar field helps to better fit the RC of spiral galaxies. In addition, new correlations are established.Comment: Latex, 5 pages with 3 Postscript figure