Magnetic excitations of the Cu2+^{2+} quantum spin chain in Sr3_3CuPtO6_6

We report the magnetic excitation spectrum as measured by inelastic neutron scattering for a polycrystalline sample of Sr$_3$CuPtO$_6$. Modeling the data by the 2+4 spinon contributions to the dynamical susceptibility within the chains, and with interchain coupling treated in the random phase approximation, accounts for the major features of the powder-averaged structure factor. The magnetic excitations broaden considerably as temperature is raised, persisting up to above 100 K and displaying a broad transition as previously seen in the susceptibility data. No spin gap is observed in the dispersive spin excitations at low momentum transfer, which is consistent with the gapless spinon continuum expected from the coordinate Bethe ansatz. However, the temperature dependence of the excitation spectrum gives evidence of some very weak interchain coupling.Comment: 9 pages, 5 figure

Assessing and Managing an Organization\u27s Green IT Maturity

Making information systems green and energy efficient is an important agenda item for many IT executives today. We present a framework of five categories (Work Practices, Office Environment, Data Centers, Procurement and Waste Management) and 64 indicators that can be customized by IT executives to assess their own organization\u27s green IT maturity. Findings based on a survey of large Korean firms using this framework are provided as an example, and guidelines for using the framework to achieve organization-specific green IT priorities are provided

Magnetic excitations of the Cu2+ quantum spin chain in Sr3CuPtO6

We report the magnetic excitation spectrum as measured by inelastic neutron scattering for a polycrystalline sample of Sr3CuPtO6. Modeling the data by the 2+4 spinon contributions to the dynamical susceptibility within the chains, and with interchain coupling treated in the random phase approximation, accounts for the major features of the powder-averaged structure factor. The magnetic excitations broaden considerably as temperature is raised, persisting up to above 100 K and displaying a broad transition as previously seen in the susceptibility data. No spin gap is observed in the dispersive spin excitations at low momentum transfer, which is consistent with the gapless spinon continuum expected from the coordinate Bethe ansatz. However, the temperature dependence of the excitation spectrum gives evidence of some very weak interchain coupling. © 2018 American Physical Societ

Mechanisms with Referrals: VCG Mechanisms and Multilevel Mechanisms

We study mechanisms for environments in which only some of the agents are directly connected to a mechanism designer and the other agents can participate in a mechanism only through the connected agents' referrals. In such environments, the mechanism designer and agents may have different interest in varying participants so that agents strategically manipulate their preference as well as their network connection to avoid competition or congestion; while the mechanism designer wants to elicit the agents' private information about both preferences and network connections. As a benchmark for an efficient mechanism, we re-define a VCG mechanism. It is incentive compatible and individually rational, but it generically runs a deficit as it requires too much compensation for referrals. Alternatively as a budget-surplus mechanism, we introduce a multilevel mechanism, in which each agent is compensated by the agents who would not be able to participate without her referrals. Under a multilevel mechanism, we show that fully referring one's acquaintances is a dominant strategy and agents have no incentive to under-report their preference if the social welfare is submodular

Magnon Breakdown in a Two Dimensional Triangular Lattice Heisenberg Antiferromagnet of Multiferroic LuMnO3

The breakdown of magnons, the quasiparticles of magnetic systems, has rarely been seen. By using an inelastic neutron scattering technique we report the observation of spontaneous magnon decay in multiferroic LuMnO$_3$, a simple two-dimensional Heisenberg triangular lattice antiferromagnet, with large spin, S = 2. The origin of this rare phenomenon lies in the non-vanishing cubic interaction between magnons in the spin Hamiltonian arising from the noncollinear 120$^o$ spin structure. We observed all three key features of the nonlinear effects as theoretically predicted: a roton-like minimum, a flat mode, and a linewidth broadening, in our inelastic neutron scattering measurements of single crystal LuMnO$_3$. Our results show that quasiparticles in a system hitherto thought of as "classical" can indeed break down