Enhanced quasiparticle heat conduction in the multigap superconductor Lu2Fe3Si5

Thermal transport measurements have been made on the Fe-based superconductor Lu2Fe3Si5 (T(c) ～ 6 K) down to a very low temperature T(c)/120. The field and temperature dependences of the thermal conductivity confirm the multigap superconductivity with fully opened gaps on the whole Fermi surfaces. In comparison to MgB2, Lu2Fe3Si5 reveals a remarkably enhanced quasiparticle heat conduction in the mixed state. The results can be interpreted as a consequence of the unequal weight of the Fe 3d-electron character among the distinct bands.     

Efficient catalytic decomposition of sulfuric acid with copper vanadates as an oxygen-generating reaction for solar thermochemical water splitting cycles

Copper pyrovanadate (Cu(2)V(2)O(7)) was found for the first time to achieve the high catalytic activity for the decomposition of sulfuric acid to evolve O(2) at moderate temperatures around 650 °C, which is essential for the development of solar thermochemical water splitting cycles.     

Oxidation of 4-Oxo-4H-1-Benzopyran-3-Carboxaldehydes with N-Bromosuccinimide

4-Oxo-4-H-1-benzopyran-3-carboxylic acids and their derivatives (esters and amides), 2, are known to possess interesting pharmacological activities.¹ As part of our synthetic studies of biologically active compounds, we needed to prepare a variety of 2 (carboxylic acids, esters, amides, etc.). An elegant method for the preparation of 4-oxo-4H-1-benzopyran-3-carboxaldehydes, 1, was reported independently by Nohara et al. ² and Harnish.³ However, despite a rather extensive effort by Nohara et al., the oxidation of 1 to 2 (Y=OH) has not been realized in good yield; thus the yields by Jones oxidation, the best reported method, ranged only from 9.5 to 39%.⁴     

Facile Synthesis of Selectively Monoprotected Unsymmetrical 1,3-Diketones from 2,2-Dimethoxyethyl Esters

Selectively monoprotected unsymmetrical 1,3-diketones were obtained by the reaction of 2,2-dimethoxyethyl esters with enamines in the presence of dichlorobis(trifiuoro-methanesulfonato)titanium.     

Effects of capacitive coupling on the escape rate in intrinsic Josephson junction stacks

We formulate a macroscopic quantum theory that can describe the macroscopic quantum tunneling (MQT) in intrinsic Josephson junctions (IJJs). The capacitively coupled IJJ model is quantized in terms of the canonical quantization method. The multi-junction effect for the MQT to the first resistive branch is clarified. It is shown that the escape rate is greatly enhanced by the capacitive coupling between junctions.     

Superconducting Pb island nanostructures studied by scanning tunneling microscopy and spectroscopy

Superconductivity of nanosized Pb-island structures whose radius is 0.8 to 2.5 times their coherence length was studied under magnetic fields using low-temperature scanning tunneling microscopy and spectroscopy. Spatial profiles of superconductivity were obtained by conductance measurements at zero-bias voltage. Critical magnetic fields for vortex penetration and expulsion and for superconductivity breaking were measured for each island. The critical fields depending on the lateral size of the islands and existence of the minimum lateral size for vortex formation were observed.     

Field-angle-dependent specific heat measurements and gap determination of a heavy fermion superconductor URu2Si2

To identify the superconducting gap structure in URu2Si2, we perform field-angle-dependent specific heat measurements for the two principal orientations in addition to field rotations, and a theoretical analysis based on microscopic calculations. The Sommerfeld coefficient gamma(H)'s in the mixed state exhibit a distinctly different field dependence. This comes from point nodes and the substantial Pauli paramagnetic effect of URu2Si2. These two features combined give rise to a consistent picture of superconducting properties, including a possible first order transition of Hc2 at low temperatures.     

Anomalous Josephson vortex solutions in Josephson junctions with multiple tunneling channels

We construct a theory for Josephson junction with multiple tunneling channels. We focus on two situations, i.e., a heterotic junction composed of two-gap-superconductor, insulator, and one-gap-superconductor, and a grain-boundary junction formed by two identical multi-gap superconductors. Then, we show that the magnetic field distribution of the Josephson vortex for ±s-wave superconductivity is much more enlarged than that for s-wave without sign change between the order parameters. We display such anomalous vortices and suggest how to evaluate the enlargement.     

Simulation study on the vortex penetration in the presence of the square antidot array

On the basis of the time-dependent Ginzburg–Landau theory we perform numerical simulations to study vortex penetration in the presence of the square antidot array. Two types of vortex penetration are demonstrated as the simulation results. The field-penetration-pattern is dependent on the size of the antidots, which is a critical factor for the direction of the vortex penetration.