BaCu3O4: High Temperature Magnetic Order in One-Dimensional S=1/2 Diamond-Chains

The magnetic properties of the alkaline earth oxocuprate BaCu3O4 are investigated. We show that the characteristic Cu3O4 layers of this material can be described with diamond chains of antiferromagnetically coupled Cu 1/2 spins with only a weak coupling between two adjacent chains. These Cu3O4 layers seem to represent a so far unique system of weakly coupled one-dimensional magnetic objects where the local AF ordering of the Cu2+ ions leads to an actual net magnetic moment of an isolated diamond chain. We demonstrate a magnetic transition at a high N\'eel temperature T_{N}=336 K

Infrared phonon dynamics of multiferroic BiFeO3 single crystal

We discuss the first infrared reflectivity measurement on a BiFeO3 single crystal between 5 K and room temperature. The 9 predicted ab-plane E phonon modes are fully and unambiguously determined. The frequencies of the 4 A1 c-axis phonons are found. These results settle issues between theory and data on ceramics. Our findings show that the softening of the lowest frequency E mode is responsible for the temperature dependence of the dielectric constant, indicating that the ferroelectric transition in BiFeO3 is soft-mode driven.Comment: 5 pages (figures included

Incommensurate spin density wave in Co-doped BaFe2As2

57Fe Mossbauer spectroscopy measurements are presented in the underdoped Ba(Fe{1-x}Cox)2As2 series for x=0.014 (T_c < 1.4K) and x=0.03 and 0.045 (T_c ~ 2 and 12K respectively). The spectral shapes in the so-called spin-density wave (SDW) phase are interpreted in terms of incommensurate modulation of the magnetic structure, and allow the shape of the modulation to be determined. In undoped BaFe2As2, the magnetic structure is commensurate, and we find that incommensurability is present at the lowest doping level (x=0.014). As Co doping increases, the low temperature modulation progressively loses its "squaredness" and tends to a sine-wave. The same trend occurs for a given doping level, as temperature increases. We find that a magnetic hyperfine component persists far above the SDW transition, its intensity being progressively tranferred to a paramagnetic component on heating.Comment: 7 pages, 8 figures, published in EP

Photon emission by an ultra-relativistic particle channeling in a periodically bent crystal

This paper is devoted to a detailed analysis of the new type of the undulator radiation generated by an ultra-relativistic charged particle channeling along a crystal plane, which is periodically bent by a transverse acoustic wave, as well as to the conditions limiting the observation of this phenomenon. This mechanism makes feasible the generation of electromagnetic radiation, both spontaneous and stimulated, emitted in a wide range of the photon energies, from X- up to gamma-rays

Orbital dichotomy of Fermi liquid properties in Sr2_2RuO4_4 revealed by Raman spectroscopy

We report a polarization-resolved Raman spectroscopy study of the orbital dependence of the quasiparticles properties in the prototypical multi-band Fermi liquid Sr\textsubscript{2}RuO\textsubscript{4}. We show that the quasiparticle scattering rate displays $\omega^{2}$ dependence as expected for a Fermi liquid. Besides, we observe a clear polarization-dependence in the energy and temperature dependence of the quasiparticle scattering rate and mass, with the $d_{xz/yz}$ orbital derived quasiparticles showing significantly more robust Fermi liquid properties than the $d_{xy}$ orbital derived ones. The observed orbital dichotomy of the quasiparticles is consistent with the picture of Sr\textsubscript{2}RuO\textsubscript{4} as a Hund's metal. Our study establishes Raman scattering as a powerful probe of Fermi liquid properties in correlated metals.Comment: 9 pages, 4 figures, Supplementary Materials available at publisher sit

Data reduction pipelines for the Keck Observatory Archive

The Keck Observatory Archive (KOA) currently serves ~ 42 TB of data spanning over 20 years from all ten past and current facility instruments at Keck. Although most of the available data are in the raw form, for four instruments (HIRES, NIRC2, OSIRIS, LWS), quick-look, browse products generated by automated pipelines are also offered to facilitate assessment of the scientific content and quality of the data. KOA underwrote the update of the MAKEE package to support reduction of the CCD upgrade to HIRES, developed scripts for reduction of NIRC2 data and automated the existing OSIRIS and LWS data reduction packages. We describe in some detail the recently completed automated pipeline for NIRSPEC, which will be used to create browse products in KOA and made available for quicklook of the data by the observers at the telescope. We review the currently available data reduction tools for Keck data, and present our plans and anticipated priorities for the development of automated pipelines and release of reduced data products for the rest of the current and future instruments. We also anticipate that Keck's newest instrument, NIRES, which will be delivered with a fully automated pipeline, will be the first to have both raw and level-1 data ingested at commissioning

Quantum cascade laser-based reflectance spectroscopy: a robust approach for the classification of plastic type

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Michel, A. P. M., Morrison, A. E., Colson, B. C., Pardis, W. A., Moya, X. A., Harb, C. C., & White, H. K. Quantum cascade laser-based reflectance spectroscopy: a robust approach for the classification of plastic type. Optics Express, 28(12), (2020): 17741-17756, doi:10.1364/OE.393231.The identification of plastic type is important for environmental applications ranging from recycling to understanding the fate of plastics in marine, atmospheric, and terrestrial environments. Infrared reflectance spectroscopy is a powerful approach for plastics identification, requiring only optical access to a sample. The use of visible and near-infrared wavelengths for plastics identification are limiting as dark colored plastics absorb at these wavelengths, producing no reflectance spectra. The use of mid-infrared wavelengths instead enables dark plastics to be identified. Here we demonstrate the capability to utilize a pulsed, widely-tunable (5.59 - 7.41 µm) mid-infrared quantum cascade laser, as the source for reflectance spectroscopy, for the rapid and robust identification of plastics. Through the application of linear discriminant analysis to the resulting spectral data set, we demonstrate that we can correctly classify five plastic types: polyethylene terephthalate (PET), high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS), with a 97% accuracy rate.Richard Saltonstall Charitable Foundation; National Academies Keck Futures Initiative (NAKFI DBS13)

Charge order near the antiferromagnetic quantum critical point in the trilayer high TcT_c cuprate HgBa2_2Ca2_2Cu3_3O8+δ_{8+ \delta}

We study the transport properties of underdoped trilayer cuprate HgBa$_2$Ca$_2$Cu$_3$O$_{8+ \delta}$ with doping level $p$ = 0.1 - 0.12 in magnetic field up to 88 T. We report for the first time in a cuprate superconductor a dramatic change of the quantum oscillation spectrum versus temperature, which is accompanied by a sign change of the Hall effect below $T \approx$ 10 K. Based on numerical simulations, we infer a Fermi surface reconstruction in the inner plane from an antiferromagnetic state (hole pockets) to a biaxial charge density wave state (electron pockets). We show that both orders compete and share the same hotspots of the Fermi surface and we discuss our result in the context of spin-fermion models.Comment: Main + Supplemental Informatio