Nodal gap structure of BaFe_2(As_{1-x}P_x)_2 from angle-resolved thermal conductivity in a magnetic field

The structure of the superconducting order parameter in the iron-pnictide superconductor BaFe$_2$(As$_{0.67}$P$_{0.33}$)$_2$ ($T_c=31$\,K) with line nodes is studied by the angle-resolved thermal conductivity measurements in a magnetic field rotated within the basal plane. We find that the thermal conductivity displays distinct fourfold oscillations with minima when the field is directed at $\pm45^\circ$ with respect to the tetragonal a-axis. We discuss possible gap structures that can account for the data, and conclude that the observed results are most consistent with the closed nodal loops located at the flat parts of the electron Fermi surface with high Fermi velocity.Comment: 4 pages, 4 figure

Line nodes in the energy gap of high-temperature superconducting BaFe_2(As_{1-x}P_x)_2 from penetration depth and thermal conductivity measurements

We report magnetic penetration depth and thermal conductivity data for high-quality single crystals of BaFe$_2$(As$_{1-x}$P$_{x}$)$_2$ ($T_c=30$\,K) which provide strong evidence that this material has line nodes in its energy gap. This is distinctly different from the nodeless gap found for (Ba,K)Fe$_2$As$_2$ which has similar $T_c$ and phase diagram. Our results indicate that repulsive electronic interactions play an essential role for Fe-based high-$T_c$ superconductivity but that uniquely there are distinctly different pairing states, with and without nodes, which have comparable $T_c$.Comment: 4 pages, 3 figures, revised version to be published in Phys. Rev. B Rapid Communicatio

Superconducting Gap Structure of LaFePO Studied by Thermal Conductivity

The superconducting gap structure of LaFePO ($T_c=7.4$K) is studied by thermal conductivity ($\kappa$) at low temperatures in fields $H$ parallel and perpendicular to the c axis. A clear two-step field dependence of $\kappa(H)$ with a characteristic field $H_s(\sim 350$ Oe) much lower than the upper critical field $H_{c2}$ is observed. In spite of large anisotropy of $H_{c2}$, $\kappa(H)$ in both $H$-directions is nearly identical below $H_s$. Above $H_s$, $\kappa(H)$ grows gradually with $H$ with a convex curvature, followed by a steep increase with strong upward curvature near $H_{c2}$. These results indicate the multigap superconductivity with active two-dimensional (2D) and passive 3D bands having contrasting gap values. Together with the recent penetration depth results, we suggest that the 2D bands consist of nodal and nodeless ones, consistent with the extended s-wave symmetry

Mid-infrared emissivity of partially dehydrated asteroid (162173) Ryugu shows strong signs of aqueous alteration

The near-Earth asteroid (162173) Ryugu, the target of Hayabusa2 space mission, was observed via both orbiter and the lander instruments. The infrared radiometer on the MASCOT lander (MARA) is the only instrument providing spectrally resolved mid-infrared (MIR) data, which is crucial for establishing a link between the asteroid material and meteorites found on Earth. Earlier studies revealed that the single boulder investigated by the lander belongs to the most common type found on Ryugu. Here we show the spectral variation of Ryugu’s emissivity using the complete set of in-situ MIR data and compare it to those of various carbonaceous chondritic meteorites, revealing similarities to the most aqueously altered ones, as well as to asteroid (101955) Bennu. The results show that Ryugu experienced strong aqueous alteration prior to any dehydration

Functional Role of Dimerization of Human Peptidylarginine Deiminase 4 (PAD4)

Peptidylarginine deiminase 4 (PAD4) is a homodimeric enzyme that catalyzes Ca2+-dependent protein citrullination, which results in the conversion of arginine to citrulline. This paper demonstrates the functional role of dimerization in the regulation of PAD4 activity. To address this question, we created a series of dimer interface mutants of PAD4. The residues Arg8, Tyr237, Asp273, Glu281, Tyr435, Arg544 and Asp547, which are located at the dimer interface, were mutated to disturb the dimer organization of PAD4. Sedimentation velocity experiments were performed to investigate the changes in the quaternary structures and the dissociation constants (Kd) between wild-type and mutant PAD4 monomers and dimers. The kinetic data indicated that disrupting the dimer interface of the enzyme decreases its enzymatic activity and calcium-binding cooperativity. The Kd values of some PAD4 mutants were much higher than that of the wild-type (WT) protein (0.45 µM) and were concomitant with lower kcat values than that of WT (13.4 s−1). The Kd values of the monomeric PAD4 mutants ranged from 16.8 to 45.6 µM, and the kcat values of the monomeric mutants ranged from 3.3 to 7.3 s−1. The kcat values of these interface mutants decreased as the Kd values increased, which suggests that the dissociation of dimers to monomers considerably influences the activity of the enzyme. Although dissociation of the enzyme reduces the activity of the enzyme, monomeric PAD4 is still active but does not display cooperative calcium binding. The ionic interaction between Arg8 and Asp547 and the Tyr435-mediated hydrophobic interaction are determinants of PAD4 dimer formation

Sample collection from asteroid (162173) Ryugu by Hayabusa2: Implications for surface evolution

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