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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Magnon-spinon dichotomy in the Kitaev hyperhoneycomb β-Li 2 IrO 3

The family of edge-sharing tricoordinated iridates and ruthenates has emerged in recent years as a major platform for Kitaev spin-liquid physics, where spins fractionalize into emergent magnetic fluxes and Majorana fermions with Dirac-like dispersions. While such exotic states are usually preempted by long-range magnetic order at low temperatures, signatures of Majorana fermions with long coherent times have been predicted to manifest at intermediate and higher energy scales, similar to the observation of spinons in quasi-one-dimensional spin chains. Here in this paper we present a resonant inelastic x-ray scattering study of the magnetic excitations of the hyperhoneycomb iridate β-Li 2 IrO 3 under a magnetic field with a record-high-resolution spectrometer. At low temperatures, dispersing spin waves can be resolved around the predicted intertwined incommensurate spiral and field-induced zigzag orders, whose excitation energy reaches a maximum of 16 meV. A 2 T magnetic field softens the dispersion around Q = 0. The behavior of the spin waves under magnetic field is consistent with our semiclassical calculations for the ground state and the dynamical spin structure factor, which further predicts that the ensued intertwined uniform states remain robust up to very high fields (100 T). Most saliently, the low-energy magnonlike mode is superimposed by a broad continuum of excitations, centered around 35 meV and extending up to 100 meV. This high-energy continuum survives up to at least 300 K—well above the ordering temperature of 38 K—and gives evidence for pairs of long-lived Majorana fermions of the proximate Kitaev spin liquid.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Signatures of non-Loudon-Fleury Raman scattering in the Kitaev magnet 𝛽−Li 2 ⁢IrO 3

We investigate the magnetic excitations of the hyperhoneycomb Kitaev magnet 𝛽−Li 2 ⁢IrO 3 by means of inelastic Raman scattering. The spectra exhibit the coexistence of a broad scattering continuum and two sharp low-energy peaks at 2.5 and 3 meV, with a distinctive polarization dependence. While the continuum is suggestive of fractional quasiparticles emerging from a proximate quantum spin liquid phase, the sharp peaks provide the first experimental signature of the “non-Loudon- Fleury” one-magnon scattering processes proposed recently. The corresponding microscopic mechanism is similar to the one leading to the symmetric off-diagonal exchange interaction Γ (because it involves a combination of both direct and ligand-mediated exchange paths) but is otherwise completely unexpected within the traditional Loudon-Fleury theory of Raman scattering. Furthermore, the present experimental verification therefore calls for a drastic reevaluation of Raman scattering in similar systems with strong spin-orbit coupling and multiple exchange paths.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Controllable Emergent Spatial Spin Modulation in Sr 2 IrO 4 by In Situ Shear Strain

Symmetric anisotropic interaction can be ferromagnetic and antiferromagnetic at the same time but for different crystallographic axes. We show that the competition of anisotropic interactions of orthogonal irreducible representations can be a general route to obtain new exotic magnetic states. We demonstrate it here by observing the emergence of a continuously tunable 12-layer spatial spin modulation when distorting the square-lattice planes in the quasi-two-dimensional antiferromagnetic Sr 2 IrO 4 under in situ shear strain. Furthermore, this translation-symmetry-breaking phase is a result of an unusual strain-activated anisotropic interaction which is at the fourth order and competing with the inherent quadratic anisotropic interaction. Such a mechanism of competing anisotropy is distinct from that among the ferromagnetic, antiferromagnetic, and/or the Dzyaloshinskii-Moriya interactions, and it could be widely applicable and highly controllable in low-dimensional magnets.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Multiple Reaction Pathways for the Oxygen Evolution Reaction May Contribute to IrO 2 (110)’s High Activity

Density functional theory calculations in conjunction with statistical mechanical arguments are performed on the rutile IrO 2 (110) facet in order to characterize multiple reaction pathways on the surface at the highest active limit (the stoichiometric surface with all metal sites available) and at the lowest active limit (the oxygen-terminated surface). Alternative pathways to the oxygen evolution reaction (OER) are found, with multiple pathways determined at each step of the four proton-coupled electron transfer reaction. Of particular interest is the detailed characterization of a co-adsorption pathway utilizing neighboring, adsorbed O, OH species in order to evolve oxygen; activation energies of this pathway are <0.5 eV and therefore easily surmountable at the high operating potentials of OER. We also determined that surface Ir atoms can potentially participate in deprotonating an OOH* intermediate; the activation energy to this is 0.67 eV on the oxygen-terminated surface. These theoretical findings explain in part the high activity present in iridium oxide catalysts and also provide insight into the mechanistic pathways available on metal oxide catalysts, which may require the concerted interaction of nearest neighbor co-adsorbates to produce chemicals of interest.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

IROS 2023 Workshop Report: Draft Guidelines on Manufacturing Procedures, Test Methods and Reporting for Soft Robotics

Soft roboticists are facing challenges with reproducibility, which prevents researchers from making holistic comparisons to prior work, impedes full understanding of results, and forces the need to “reinvent the wheel,” delaying fundamental advances. Reproducibility of results is key to advancing science as well as achieving technology transfer from research laboratories to industrial applications. Recently, a discussion-based workshop dedicated to the topic, “Developing Standard Testing and Reporting Guidelines for Soft Robotics,” was held at IROS 2023 in Detroit, MI. The purpose of this document is to record a set of recommendations and voluntary draft guidelines for soft roboticists concerning fabrication/manufacturing, test procedures, and reporting, which were collectively developed at the workshop. Together as a community, we hope to improve the reporting standards of soft robotics and drive the field as a whole toward more rigorous research practices.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Materials Data on IrOs by Materials Project

OsIr is Magnesium-derived structured and crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Os is bonded to six equivalent Os and six equivalent Ir atoms to form OsIr6Os6 cuboctahedra that share corners with eighteen equivalent OsIr6Os6 cuboctahedra, edges with six equivalent OsIr6Os6 cuboctahedra, edges with twelve equivalent IrIr6Os6 cuboctahedra, faces with eight equivalent OsIr6Os6 cuboctahedra, and faces with twelve equivalent IrIr6Os6 cuboctahedra. All Os–Os bond lengths are 2.76 Å. All Os–Ir bond lengths are 2.71 Å. Ir is bonded to six equivalent Os and six equivalent Ir atoms to form IrIr6Os6 cuboctahedra that share corners with eighteen equivalent IrIr6Os6 cuboctahedra, edges with six equivalent IrIr6Os6 cuboctahedra, edges with twelve equivalent OsIr6Os6 cuboctahedra, faces with eight equivalent IrIr6Os6 cuboctahedra, and faces with twelve equivalent OsIr6Os6 cuboctahedra. All Ir–Ir bond lengths are 2.76 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CeB4(IrOs)2 by Materials Project

CeB4(OsIr)2 is alpha Pu-derived structured and crystallizes in the tetragonal P4_2 space group. The structure is three-dimensional. Ce3+ is bonded in a 4-coordinate geometry to four B+1.50- atoms. All Ce–B bond lengths are 2.92 Å. Os2- is bonded in a 4-coordinate geometry to four B+1.50- atoms. There are a spread of Os–B bond distances ranging from 2.13–2.18 Å. Ir+3.50+ is bonded in a 4-coordinate geometry to four B+1.50- atoms. There are a spread of Ir–B bond distances ranging from 2.12–2.19 Å. There are two inequivalent B+1.50- sites. In the first B+1.50- site, B+1.50- is bonded in a 5-coordinate geometry to one Ce3+, three equivalent Os2-, one Ir+3.50+, and one B+1.50- atom. The B–B bond length is 1.81 Å. In the second B+1.50- site, B+1.50- is bonded in a 6-coordinate geometry to one Ce3+, one Os2-, three equivalent Ir+3.50+, and one B+1.50- atom.

36 MATERIALS SCIENCE↗