83 research outputs found
Topological Magnon Bands in a Kagome Lattice Ferromagnet
There is great interest in finding materials possessing quasiparticles with topological properties. Such materials may have novel excitations that exist on their boundaries which are protected against disorder. We report experimental evidence that magnons in an insulating kagome ferromagnet can have a topological band structure. Our neutron scattering measurements further reveal that one of the bands is flat due to the unique geometry of the kagome lattice. Spin wave calculations show that the measured band structure follows from a simple Heisenberg Hamiltonian with a Dzyaloshinkii-Moriya interaction. This serves as the first realization of an effectively two-dimensional topological magnon insulator—a new class of magnetic material that should display both a magnon Hall effect and protected chiral edge modes.United States. Dept. of Energy. Office of Basic Energy Sciences (Grant DE-FG02-07ER46134)National Science Foundation (U.S.) (Grant CHE 1041863
Detonation Initiation via Imploding Shock Waves
An imploding annular shock wave driven by a jet of air was used to initiate detonations
inside a 76 mm diameter tube. The tube was filled with a test gas composed of either
stoichiometric ethylene-oxygen or propane-oxygen diluted with nitrogen. The strength of
the imploding shock wave and the sensitivity of the test gas were varied in an effort to
find the minimum shock strength required for detonation of each test mixture. The results
show that the minimum required shock strength increases with mixture sensitivity and
suggest that impractically large shock driver pressures are required to initiate detonations
in ethylene-air or propane-air mixtures when using this technique
A Cu2+ (S = 1/2) Kagom\'e Antiferromagnet: MgxCu4-x(OH)6Cl2
Spin-frustrated systems are one avenue for inducing macroscopic quantum
states in materials. However, experimental realization of this goal has been
difficult because of the lack of simple materials and, if available, the
separation of the unusual magnetic properties arising from exotic magnetic
states from behavior associated with chemical disorder, such as site mixing.
Here we report the synthesis and magnetic properties of a new series of
magnetically frustrated materials, MgxCu4-x(OH)6Cl2. Because of the
substantially different ligand-field chemistry of Mg2+ and Cu2+, site disorder
within the kagom\'e layers is minimized, as directly measured by X-ray
diffraction. Our results reveal that many of the properties of these materials
and related systems are not due to disorder of the magnetic lattice but rather
reflect an unusual ground state.Comment: Accepted for publication in J. Am. Chem. Soc
Magnetic transitions in the topological magnon insulator Cu(1,3-bdc)
Topological magnon insulators are a new class of magnetic materials that
possess topologically nontrivial magnon bands. As a result, magnons in these
materials display properties analogous to those of electrons in topological
insulators. Here, we present magnetization, specific heat, and neutron
scattering measurements of the ferromagnetic kagome magnet Cu(1,3-bdc). Our
measurements provide a detailed description of the magnetic structure and
interactions in this material, and confirm that it is an ideal prototype for
topological magnon physics in a system with a simple spin Hamiltonian.Comment: 10 pages, 10 figure
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