Unconventional Superconductivity in the BiS_{2}-Based Layered Superconductor NdO_{0.71}F_{0.29}BiS_{2}.

We investigate the superconducting-gap anisotropy in one of the recently discovered BiS_{2}-based superconductors, NdO_{0.71}F_{0.29}BiS_{2} (T_{c}∼5 K), using laser-based angle-resolved photoemission spectroscopy. Whereas the previously discovered high-T_{c} superconductors such as copper oxides and iron-based superconductors, which are believed to have unconventional superconducting mechanisms, have 3d electrons in their conduction bands, the conduction band of BiS_{2}-based superconductors mainly consists of Bi 6p electrons, and, hence, the conventional superconducting mechanism might be expected. Contrary to this expectation, we observe a strongly anisotropic superconducting gap. This result strongly suggests that the pairing mechanism for NdO_{0.71}F_{0.29}BiS_{2} is an unconventional one and we attribute the observed anisotropy to competitive or cooperative multiple paring interactions.

Advancement of Periosteal and Capsular Complexes With or Without Augmentation Using a Free Graft From Lower Extensor Retinaculum: A Comparative Study With Propensity Score Matching.

Background: This study compared the outcome of the L-shaped (L-AD) advancement of the periosteal and capsular complexes with or without augmentation using a free graft of the lower extensor retinaculum (AUG) in patients with chronic lateral ankle instability. Methods: A matched pair analysis was performed of retrospectively collected medical records of patients undergoing lateral ankle ligament repair who had completed at least 2 years of follow-up. Patients who underwent L-AD with AUG and patients undergoing L-AD alone were matched for age, sex, stress radiography findings, and body mass index. Patients with general joint laxity, osteoarthritic changes in the ankle, and subtalar symptoms and who underwent simultaneous surgical treatment for conditions other than that for lateral ankle ligament were excluded. A total of 46 patients were included in the study (23 patients in each group). Clinical outcome scores and postoperative mechanical instability were compared. Results: The median American Orthopaedic Foot & Ankle Society (AOFAS) score improved significantly (P < .001) from 72 to 97 in the L-AD alone group and from 77 to 100 in the L-AD with AUG group. The mean (±SD) talar tilt angles improved significantly from 11.1 to 4.7 degrees postoperatively (P < .001) in the L-AD alone group vs 9.7 to 5.2 degrees (P < .001) in the L-AD with AUG group. The mean anterior drawer distances were improved significantly postoperatively from 6.4 to 4.7 mm (P < .001) in the L-AD alone group, and from 6.5 to 4.5 mm (P < .001) in the L-AD with AUG group. Conclusion: The L-AD technique significantly improved AOFAS scores and mechanical instability of ankles with chronic lateral instability with a very low complication rate. Additional augmentation using a free graft showed no advantages in the ankle with a talar tilt of <20 degrees. Level of Evidence: Level III, retrospective case-control series.

Solvothermal synthesis of n-type Bi2(SexTe1-x)3 nanoplates for high-performance thermoelectric thin films on flexible substrates.

To improve thermoelectric performance of materials, the utilization of low-dimensional materials with a multi-alloy system is a promising approach. We report on the enhanced thermoelectric properties of n-type Bi2(SexTe1-x)3 nanoplates using solvothermal synthesis by tuning the composition of selenium (Se). Variation of the Se composition within nanoplates is demonstrated using X-ray diffraction and electron probe microanalysis. The calculated lattice parameters closely followed Vegard's law. However, when the Se composition was extremely high, an impurity phase was observed. At a reduced Se composition, regular-hexagonal-shaped nanoplates with a size of approximately 500 nm were produced. When the Se composition was increased, the shape distribution became random with sizes more than 5 µm. To measure the thermoelectric properties, nanoplate thin films (NPTs) were formed on a flexible substrate using drop-casting, followed by thermal annealing. The resulting NPTs sufficiently adhered to the substrate during the bending condition. The electrical conductivity of the NPTs increased with an increase in the Se composition, but it rapidly decreased at an extremely high Se composition because of the presence of the impurity phase. As a result, the Bi2(SexTe1-x)3 NPTs exhibited the highest power factor of 4.1 µW/(cm∙K2) at a Se composition of x = 0.75. Therefore, it was demonstrated that the thermoelectric performance of Bi2(SexTe1-x)3 nanoplates can be improved by tuning the Se composition.

Bose-Einstein condensation superconductivity induced by disappearance of the nematic state.

The crossover from the superconductivity of the Bardeen-Cooper-Schrieffer (BCS) regime to the Bose-Einstein condensation (BEC) regime holds a key to understanding the nature of pairing and condensation of fermions. It has been mainly studied in ultracold atoms, but in solid systems, fundamentally previously unknown insights may be obtained because multiple energy bands and coexisting electronic orders strongly affect spin and orbital degrees of freedom. Here, we provide evidence for the BCS-BEC crossover in iron-based superconductors FeSe1 - x S x from laser-excited angle-resolved photoemission spectroscopy. The system enters the BEC regime with x = 0.21, where the nematic state that breaks the orbital degeneracy is fully suppressed. The substitution dependence is opposite to the expectation for single-band superconductors, which calls for a new mechanism of BCS-BEC crossover in this system.

Superconducting pairing of topological surface states in bismuth selenide films on niobium.

A topological insulator film coupled to a simple isotropic s-wave superconductor substrate can foster helical pairing of the Dirac fermions associated with the topological surface states. Experimental realization of such a system is exceedingly difficult, however using a novel "flip-chip" technique, we have prepared single-crystalline Bi2Se3 films with predetermined thicknesses in terms of quintuple layers (QLs) on top of Nb substrates fresh from in situ cleavage. Our angle-resolved photoemission spectroscopy (ARPES) measurements of the film surface disclose superconducting gaps and coherence peaks of similar magnitude for both the topological surface states and bulk states. The ARPES spectral map as a function of temperature and film thickness up to 10 QLs reveals key characteristics relevant to the mechanism of coupling between the topological surface states and the superconducting Nb substrate; the effective coupling length is found to be much larger than the decay length of the topological surface states.

Superconducting gap anisotropy sensitive to nematic domains in FeSe.

The structure of the superconducting gap in unconventional superconductors holds a key to understand the momentum-dependent pairing interactions. In superconducting FeSe, there have been controversial results reporting nodal and nodeless gap structures, raising a fundamental issue of pairing mechanisms of iron-based superconductivity. Here, by utilizing polarization-dependent laser-excited angle-resolved photoemission spectroscopy, we report a detailed momentum dependence of the gap in single- and multi-domain regions of orthorhombic FeSe crystals. We confirm that the superconducting gap has a twofold in-plane anisotropy, associated with the nematicity due to orbital ordering. In twinned regions, we clearly find finite gap minima near the vertices of the major axis of the elliptical zone-centered Fermi surface, indicating a nodeless state. In contrast, the single-domain gap drops steeply to zero in a narrow angle range, evidencing for nascent nodes. Such unusual node lifting in multi-domain regions can be explained by the nematicity-induced time-reversal symmetry breaking near the twin boundaries.

Observation of topological superconductivity on the surface of an iron-based superconductor.

Topological superconductors are predicted to host exotic Majorana states that obey non-Abelian statistics and can be used to implement a topological quantum computer. Most of the proposed topological superconductors are realized in difficult-to-fabricate heterostructures at very low temperatures. By using high-resolution spin-resolved and angle-resolved photoelectron spectroscopy, we find that the iron-based superconductor FeTe1-x Se x (x = 0.45; superconducting transition temperature Tc = 14.5 kelvin) hosts Dirac-cone-type spin-helical surface states at the Fermi level; the surface states exhibit an s-wave superconducting gap below Tc Our study shows that the surface states of FeTe0.55Se0.45 are topologically superconducting, providing a simple and possibly high-temperature platform for realizing Majorana states.

Establishment of serological test to detect antibody against ferret coronavirus.

Since there is no available serological methods to detect antibodies to ferret coronavirus (FRCoV), an enzyme-linked immunosorbent assay (ELISA) using recombinant partial nucleocapsid (N) proteins of the ferret coronavirus (FRCoV) Yamaguchi-1 strain was developed to establish a serological method for detection of FRCoV infection. Many serum samples collected from ferrets recognized both a.a. 1-179 and a.a. 180-374 of the N protein, but two serum samples did not a.a. 180-374 of the N protein. This different reactivity was also confirmed by immunoblot analysis using the serum from the ferret.Therefore, the a.a. 1-179 of the N protein was used as an ELISA antigen. Serological test was carried out using sera or plasma of ferrets in Japan. Surprisingly, 89% ferrets in Japan had been infected with FRCoV. These results indicated that our established ELISA using a.a. 1-179 of the N protein is useful for detection of antibody to FRCoV for diagnosis and seroepidemiology of FRCoV infection.