6,295 research outputs found
Origin of the insulating state in honeycomb iridates and rhodates
A burning question in the emerging field of spin-orbit driven insulating
iridates, such as Na2IrO3 and Li2IrO3 is whether the observed insulating state
should be classified as a Mott-Hubbard insulator derived from a half-filled
relativistic j_eff=1/2 band or as a band insulator where the gap is assisted by
spin-orbit interaction, or Coulomb correlations, or both. The difference
between these two interpretations is that only for the former, strong
spin-orbit coupling (lambda >~ W, where W is the band width) is essential. We
have synthesized the isostructural and isoelectronic Li2RhO3 and report its
electrical resistivity and magnetic susceptibility. Remarkably it shows
insulating behavior together with fluctuating effective S=1/2 moments, similar
to Na2IrO3 and Li2IrO3, although in Rh4+ (4d5) the spin-orbit coupling is
greatly reduced. We show that this behavior has non-relativistic one-electron
origin (although Coulomb correlations assist in opening the gap), and can be
traced down to formation of quasi-molecular orbitals, similar to those in
Na2IrO3.Comment: 7 pages, 7 figure
Reinforcing the link between the double red clump and the X-shaped bulge of the Milky Way
The finding of a double red clump in the luminosity function of the Milky Way bulge has been interpreted as evidence for an X-shaped structure. Recently, an alternative explanation has been suggested, where the double red clump is an effect of multiple stellar populations in a classical spheroid. In this Letter we provide an observational assessment of this scenario and show that it is not consistent with the behaviour of the red clump across different lines of sight, particularly at high distances from the Galactic plane. Instead, we confirm that the shape of the red clump magnitude distribution closely follows the distance distribution expected for an X-shaped bulge at critical Galactic latitudes. We also emphasize some key observational properties of the bulge red clump that should not be neglected in the search for alternative scenarios
Photo-oxidative and soil burial degradation of irrigation tubes based on biodegradable polymer blends
Irrigation tubes based on biodegradable polymers were prepared via an extrusion-drawing process by Irritec and compared to conventional pipes made of high-density polyethylene (HDPE). A commercial polylactide/poly (butyleneadipate-co-butyleneterephthalate) (PLA/PBAT) blend (Bio-Flex®) and Mater-Bi® were used. The polymers were characterized from rheological and mechanical points of view. Irrigation pipes were subjected to photoaging with continued exposure to UV radiation up to 22 days. The degradability in the soil of irrigation tube samples was studied. The influence of temperature and UV irradiation on soil burial degradation was investigated. A soil burial degradation test was carried out at 30 °C and 50 °C for up to 70 days. The degree of degradation was evaluated from the weight loss percentage. The degradation rate of irrigation tube samples based on Mater-Bi® was higher at 30 °C and was stimulated after 14 days of UV irradiation. Higher temperatures or UV aging encouraged the disintegration in soil of Bio-Flex®-based irrigation tubes. Furthermore, tube samples, before and after UV and soil burial degradation, were analyzed by Attenuated Total Reflection-Fourier Transform Infra-Red (ATR-FTIR) spectroscop
Effect of isoelectronic doping on honeycomb lattice iridate A_2IrO_3
We have investigated experimentally and theoretically the series
(NaLi)IrO. Contrary to what has been believed so far,
only for the system forms uniform solid solutions. For larger Li
content, as evidenced by powder X-ray diffraction, scanning electron microscopy
and density functional theory calculations, the system shows a miscibility gap
and a phase separation into an ordered NaLiIrO phase with
alternating Na and LiIrO planes, and a Li-rich phase close to pure
LiIrO. For we observe (1) an increase of with Li
doping up to , despite the fact that in pure LiIrO is
smaller than in NaIrO, and (2) a gradual reduction of the
antiferromagnetic ordering temperature and ordered moment. The
previously proposed magnetic quantum phase transition at may
occur in a multiphase region and its nature needs to be re-evaluated.Comment: 8 pages, 9 figures including supplemental informatio
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