Magnetic excitations in coupled Haldane spin chains near the quantum critical point

Two quasi-1-dimensional S=1 quantum antiferromagnetic materials, PbNi2V2O8 and SrNi2V2O8, are studied by inelastic neutron scattering on powder samples. While magnetic interactions in the two systems are found to be very similar, subtle differences in inter-chain interaction strengths and magnetic anisotropy are detected. The latter are shown to be responsible for qualitatively different ground state properties: magnetic long-range order in SrNi2V2O8 and disordered ``spin liquid'' Haldane-gap state in PbNi2V2O8.Comment: 15 figures, Figs. 5,9, and 10 in color. Some figures in JPEG format. Complete PostScript and PDF available from http://papillon.phy.bnl.gov/publicat.ht

Field-induced commensurate long-range order in the Haldane-gap system NDMAZ

High-field neutron diffraction studies of the new quantum-disordered S=1 linear-chain antiferromagnet Ni(C$_5$H$_{14}$N$_2$)$_2$N$_3$(ClO$_4$) (NDMAZ) are reported. At T=70 mK, at a critical field $H_c=13.4$ T applied along the (013) direction, a phase transition to a commensurate N\'{e}el-like ordered state is observed. The results are discussed in the context of existing theories of quantum phase transitions in Haldane-gap antiferromagnets, and in comparions with previous studies of the related system Ni(C$_5$H$_{14}$N$_2$)$_2$N$_3$(PF$_6$)

Using a Geographical Information System to Evaluate Contributing Factors to Deer-Vehicle Collisions

An expanding human population combined with a growing white-tailed deer (Odocoifeus virginianus) population has resulted in an increase of deer-vehicle collisions in Arkansas. In response to this increase, we are using spatially explicit datasets integrated within a geographic information system (GIS) to identify county-level and site-specific factors contributing to deer-vehicle collisions. County-level information, such as human population densities /urbanization, deer density indices, and road densities, is being evaluated for use in identifying potential aggregations of deer-vehicle collisions. Site-specific information being evaluated includes physical factors such as landcover composition and arrangement, topography, and road characteristics. By incorporating these multi-scale data sets in a GIS, spatial intersections of variables indicating potential current or future hotspots of deer-vehicle collisions can be identified and mapped. This information can then be used to aid administrators and natural resource managers in identifying locations where deer-vehicle collisions may be concentrated

Reduction of the spin susceptibility in the superconducting state of Sr2RuO4 observed by polarized neutron scattering

Recent observations [A.~Pustogow et al. Nature 574, 72 (2019)] of a drop of the $^{17}$O nuclear magnetic resonance (NMR) Knight shift in the superconducting state of Sr$_2$RuO$_4$ challenged the popular picture of a chiral odd-parity paired state in this compound. Here we use polarized neutron scattering to show that there is a $34 \pm 6$ % drop in the magnetic susceptibility at the ruthenium site below the superconducting transition temperature. Measurements are made at lower fields $H \sim \tfrac{1}{3} H_{c2}$ than a previous study allowing the suppression to be observed. Our results are consistent with the recent NMR observations and rule out the chiral odd-parity $\mathbf{d}=\hat{\mathbf{z}}(k_x\pm ik_y)$ state. The observed susceptibility is consistent with several recent proposals including even-parity $B_{1g}$ and odd-parity helical states.Comment: New version with Supplementary Material discussing orbital contributions to the susceptibility, Fermi liquid corrections and a two fluid mode

Novel Polyoxometalate- Ionic Liquid with Antibacterial and Antifungal Properties. Feasibility of Its Implementation As a Multifunctional Thin Coating

The synthesis of hybrid materials, combining the properties of organic and inorganic components, results in composites with unique physical and chemical features. Polyoxometalates (POMs), i.e. inorganic anionic molecular metal oxides, are considered as promising future metallodrugs due to their antiviral, antitumoral and antibacterial activities. The combination of bulky organic cations with POMs results in composite ionic liquids (IL; melting point below 100°C) which combine the unique properties of both components. Pioneering studies have used composites of alkylammonium cations and POM anions for multifunctional water purification to remove toxic heavy materials, organic aromatics and microbes and for the inhibition of bio-corrosion on metal and stone surfaces due to coating formation.Fil: Enderle, Ana Gabriela. Universidad Nacional del Litoral; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Streb, C.. Universitat Ulm; AlemaniaFil: Bollini, Mariela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Bionanociencias "Elizabeth Jares Erijman"; ArgentinaFil: Culzoni, Maria Julia. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Química. Cátedra de Química Analítica; ArgentinaFil: Mitchell, S. G.. Universidad de Zaragoza; EspañaFil: Franco Castillo, I.. Universidad de Zaragoza; España2019 AIChE Annual MeetingOrlandoEstados UnidosAmerican Institute of Chemical Engineer

Jahn-Teller versus quantum effects in the spin-orbital material LuVO3

We report on combined neutron and resonant x-ray scattering results, identifying the nature of the spin-orbital ground state and magnetic excitations in LuVO3 as driven by the orbital parameter. In particular, we distinguish between models based on orbital Peierls dimerization, taken as a signature of quantum effects in orbitals, and Jahn-Teller distortions, in favor of the latter. In order to solve this long-standing puzzle, polarized neutron beams were employed as a prerequisite in order to solve details of the magnetic structure, which allowed quantitative intensity-analysis of extended magnetic excitation data sets. The results of this detailed study enabled us to draw definite conclusions about classical vs quantum behavior of orbitals in this system and to discard the previous claims about quantum effects dominating the orbital physics of LuVO3 and similar systems.Comment: Phys. Rev. B 91, 161104(R) (2015

Evidence for Kosterlitz-Thouless type orientational ordering of CF3_3Br monolayers physisorbed on graphite

Monolayers of the halomethane CF$_3$Br adsorbed on graphite have been investigated by x-ray diffraction. The layers crystallize in a commensurate triangular lattice. On cooling they approach a three-sublattice antiferroelectric pattern of the in-plane components of the dipole moments. The ordering is not consistent with a conventional phase transition, but points to Kosterlitz-Thouless behavior. It is argued that the transition is described by a 6-state clock model on a triangular lattice with antiferromagnetic nearest neighbor interactions which is studied with Monte-Carlo simulations. A finite-size scaling analysis shows that the ordering transition is indeed in the KT universality class.Comment: 4 pages, 5 figure

Longitudinal magnon in the tetrahedral spin system Cu2Te2O5Br2 near quantum criticality

We present a comprehensive study of the coupled tetrahedra-compound Cu2Te2O5Br2 by theory and experiments in external magnetic fields. We report the observation of a longitudinal magnon in Raman scattering in the ordered state close to quantum criticality. We show that the excited tetrahedral-singlet sets the energy scale for the magnetic ordering temperature T_N. This energy is determined experimentally. The ordering temperature T_N has an inverse-log dependence on the coupling parameters near quantum criticality

Coexistence of Haldane gap excitations and long range antiferromagnetic order in mixed-spin nickelates R_2 Ba Ni O_5

The spin dynamics of the S=1 Ni-chains in mixed-spin antiferromagnets Pr_2 Ba Ni O_5 and Nd_x Y_2-x Ba Ni O_5 is described in terms of a simple Ginzburg-Landau Lagrangian coupled to the sublattice of rare-earth ions. Within this framework we obtain a theoretical explanation for the experimentally observed coexistence of Haldane gap excitations and long-range magnetic order, as well as for the increase of the Haldane gap energy below the Neel point. We also predict that the degeneracy of the Haldane triplet is lifted in the magnetically ordered phase. The theoretical results are consistent with the available experimental data.Comment: 4 pages, 1 figure, submitted to PRL An alternative derivation of main results and new references adde