Strong Spin-Phonon Coupling Mediated by Single Ion Anisotropy in the All-In-All-Out Pyrochlore Magnet Cd_{2}Os_{2}O_{7}.

Spin-phonon coupling mediated by single ion anisotropy was investigated using optical spectroscopy and first-principles calculations in the all-in-all-out pyrochlore magnet Cd_{2}Os_{2}O_{7}. Clear anomalies were observed in both the phonon frequencies and linewidths at the magnetic ordering temperature. The renormalization of the phonon modes was exceptionally large, signifying the presence of an unconventional magnetoelastic term from large spin-orbit coupling. In addition, the relative phonon frequency shifts show a strong correlation with the modulation of noncubic crystal field by the corresponding lattice distortion. Our observation establishes a new type of spin-phonon coupling through single ion anisotropy, a second-order spin-orbit coupling term, in Cd_{2}Os_{2}O_{7}.

One-Third Magnetization Plateau with a Preceding Novel Phase in Volborthite.

We have synthesized high-quality single crystals of volborthite, a seemingly distorted kagome antiferromagnet, and carried out high-field magnetization measurements up to 74 T and ^{51}V NMR measurements up to 30 T. An extremely wide 1/3 magnetization plateau appears above 28 T and continues over 74 T at 1.4 K, which has not been observed in previous studies using polycrystalline samples. NMR spectra reveal an incommensurate order (most likely a spin-density wave order) below 22 T and a simple spin structure in the plateau phase. Moreover, a novel intermediate phase is found between 23 and 26 T, where the magnetization varies linearly with magnetic field and the NMR spectra indicate an inhomogeneous distribution of the internal magnetic field. This sequence of phases in volborthite bears a striking similarity to those of frustrated spin chains with a ferromagnetic nearest-neighbor coupling J_{1} competing with an antiferromagnetic next-nearest-neighbor coupling J_{2}.

Optical Spectroscopic Studies of the Metal-Insulator Transition Driven by All-In-All-Out Magnetic Ordering in 5d Pyrochlore Cd(2)Os(2)O(7).

We investigated the metal-insulator transition (MIT) driven by all-in-all-out (AIAO) antiferromagnetic ordering in the 5d pyrochlore Cd(2)Os(2)O(7) using optical spectroscopy and first-principles calculations. We showed that the temperature evolution in the band-gap edge and free carrier density were consistent with rigid upward (downward) shifts of electron (hole) bands, similar to the case of Lifshitz transitions. The delicate relationship between the band gap and free carrier density provides experimental evidence for the presence of an AIAO metallic phase, a natural consequence of such MITs. The associated spectral weight change at high energy and first-principles calculations further support the origin of the MIT from the band shift near the Fermi level. Our data consistently support that the MIT induced by AIAO ordering in Cd(2)Os(2)O(7) is not close to a Slater type but instead to a Lifshitz type.

Tetrahedral magnetic order and the metal-insulator transition in the pyrochlore lattice of Cd2Os2O7.

Cd2Os2O7 shows a peculiar metal-insulator transition at 227 K with magnetic ordering in a frustrated pyrochlore lattice, but its magnetic structure in the ordered state and the transition origin are yet uncovered. We observed a commensurate magnetic peak by resonant x-ray scattering in a high-quality single crystal. X-ray diffraction and Raman scattering experiments confirmed that the transition is not accompanied with any spatial symmetry breaking. We propose a noncollinear all-in-all-out spin arrangement on the tetrahedral network made of Os atoms. Based on this we suggest that the transition is not caused by the Slater mechanism as believed earlier but by an alternative mechanism related to the formation of the specific tetrahedral magnetic order on the pyrochlore lattice in the presence of strong spin-orbit interactions.

De novo sequencing of highly modified therapeutic oligonucleotides by hydrophobic tag sequencing coupled with LC-MS.

Correct sequences are prerequisite for quality control of therapeutic oligonucleotides. However, there is no definitive method available for determining sequences of highly modified therapeutic RNAs, and thereby, most of the oligonucleotides have been used clinically without direct sequence determination. In this study, we developed a novel sequencing method called 'hydrophobic tag sequencing'. Highly modified oligonucleotides are sequenced by partially digesting oligonucleotides conjugated with a 5'-hydrophobic tag, followed by liquid chromatography-mass spectrometry analysis. 5'-Hydrophobic tag-printed fragments (5'-tag degradates) can be separated in order of their molecular masses from tag-free oligonucleotides by reversed-phase liquid chromatography. As models for the sequencing, the anti-VEGF aptamer (Macugen) and the highly modified 38-mer RNA sequences were analyzed under blind conditions. Most nucleotides were identified from the molecular weight of hydrophobic 5'-tag degradates calculated from monoisotopic mass in simple full mass data. When monoisotopic mass could not be assigned, the nucleotide was estimated using the molecular weight of the most abundant mass. The sequences of Macugen and 38-mer RNA perfectly matched the theoretical sequences. The hydrophobic tag sequencing worked well to obtain simple full mass data, resulting in accurate and clear sequencing. The present study provides for the first time a de novo sequencing technology for highly modified RNAs and contributes to quality control of therapeutic oligonucleotides. Copyright © 2016 John Wiley & Sons, Ltd.

Two-magnon scattering in the 5d all-in-all-out pyrochlore magnet Cd2Os2O7.

5d pyrochlore oxides with all-in-all-out magnetic order are prime candidates for realizing strongly correlated, topological phases of matter. Despite significant effort, a full understanding of all-in-all-out magnetism remains elusive as the associated magnetic excitations have proven difficult to access with conventional techniques. Here we report a Raman spectroscopy study of spin dynamics in the all-in-all-out magnetic state of the 5d pyrochlore Cd2Os2O7. Through a comparison between the two-magnon scattering and spin-wave theory, we confirm the large single ion anisotropy in this material and show that the Dzyaloshinskii-Moriya and exchange interactions play a significant role in the spin-wave dispersions. The Raman data also reveal complex spin-charge-lattice coupling and indicate that the metal-insulator transition in Cd2Os2O7 is Lifshitz-type. Our work establishes Raman scattering as a simple and powerful method for exploring the spin dynamics in 5d pyrochlore magnets.Pyrochlore 5d transition metal oxides are expected to have interesting forms of magnetic order but are hard to study with conventional probes. Here the authors show that Raman scattering can be used to measure magnetic excitations in Cd2Os2O7 and that it exhibits complex spin-charge-lattice coupling.

Author Correction: Two-magnon scattering in the 5d all-in-all-out pyrochlore magnet Cd2Os2O7.

A correction to this article has been published and is linked from the HTML version of this article.

Isotropically gapped strong-coupling superconductivity in the beta-pyrochlore KOs2O6: evidence from penetration depth measurements.

We report on measurements of the temperature dependence of the magnetic penetration depth down to 0.04 K in a high-quality sample of the beta-pyrochlore KOs2O6 (Tc=9.65 K) with a spin-frustrated lattice. We observe temperature-independent behavior below T approximately 0.3Tc, which is firm evidence for the presence of an isotropic superconducting gap in this material. In the whole temperature range the superfluid density is very well described, without the need of adjustable parameters, by a strong-coupling extension of the BCS model for an isotropic gap. Thus, the penetration depth results indicate that KOs2O6 is a strong-coupling superconductor with a fully developed energy gap. No effect of the second phase transition taking place at Tp=7.5 K was observed on the penetration depth, which suggests that the Cooper pairs remain unperturbed across this transition.

Vortex redistribution below the first-order transition temperature in the beta-pyrochlore superconductor KOs2O6.

A miniature Hall-sensor array was used to detect magnetic induction locally in the vortex states of the beta-pyrochlore superconductor KOs2O6. Below the first-order transition at T{p} approximately 8 K, which is associated with a change in the rattling motion of K ions, the lower critical field and the remanent magnetization both show a distinct decrease, suggesting that the electron-phonon coupling is weakened below the transition. At high magnetic fields, the local induction shows an unexpectedly large jump at T{p} whose sign changes with position inside the sample. Our results demonstrate a novel redistribution of vortices whose energy is reduced abruptly below the first-order transition at T{p}.

effects of rattling phonons on the dynamics of quasiparticle excitation in the beta-pyrochlore KOs(2)O(6) Superconductor.

Microwave penetration depth lambda and surface resistance at 27 GHz are measured in high quality crystals of KOs(2)O(6). Firm evidence for fully gapped superconductivity is provided from lambda(T). Below the second transition at T(p) approximately 8 K, the superfluid density shows a steplike change with a suppression of effective critical temperature T(c). Concurrently, the extracted quasiparticle scattering time shows a steep enhancement, indicating a strong coupling between the anomalous rattling motion of K ions and quasiparticles. The results imply that the rattling phonons help to enhance superconductivity, and that K sites freeze to an ordered state with long quasiparticle mean free path below T(p).

Interplay of superconductivity and rattling phenomena in beta-pyrochlore KOs2O6 studied by photoemission spectroscopy.

The electronic structure near the Fermi level (EF) of the beta-pyrochlore superconductor KOs2O6 is studied using laser-excited ultrahigh-resolution photoemission spectroscopy. The superconducting gap clearly opens across the superconducting transition (Tc=9.6 K), with the strong electron-phonon coupling value of 2Delta(0)/k B Tc>or=4.56. A fitting analysis identifies clear anomalies at Tp=7.5 K in the temperature dependencies of the superconducting gap size and the quasiparticle relaxation lifetime. These anomalies and the fine spectral structures arising from phonons suggest that the existence of the rattling behavior of K ions significantly affects the superconductivity in KOs2O6.

A transient ghrelin surge occurs just before feeding in a scheduled meal-fed sheep.

Ghrelin, a gastric-derived peptide, has recently been identified as an endogenous natural ligand for the growth hormone (GH) secretagogue receptor. However, secretory characteristics of ghrelin are still obscure in ruminants. To investigate the diurnal rhythm in ghrelin secretion and its relationship to GH secretion, plasma ghrelin and GH concentrations were determined in Suffolk rams fed with a roughage diet once daily (Experiment 1). Abrupt increases (P<0.05) in plasma ghrelin occurred just before a meal-feeding compared with that at 1h before feeding, then rapidly fell with a minimum during the feeding. A pulsatile surge (P<0.01) in plasma GH concentrations, which seemed to follow a single surge in plasma ghrelin, was observed during the feeding. In Experiment 2, plasma ghrelin and GH were determined in sheep subjected to a pseudo-feeding of 2h to determine whether feed ingestion itself influences ghrelin and GH secretions. Compared with those at 1h before feeding, a tendency of increases (P<0.1) in plasma ghrelin and significant increases (P<0.05) in GH occurred just before and during a pseudo-feeding, respectively. Plasma ghrelin temporally declined within 1h after the start of the pseudo-feeding, and increased again and maintained higher levels during the last period of the pseudo-feeding. These results suggest that the transient surge of ghrelin secretion just before a scheduled meal feeding would not be due to the ingestion of feed, and that a pulsatile increase in plasma GH during the actual- or pseudo-feeding could be induced by the transient ghrelin surge.