Stoichiometric Ternary Superhydride LaBeH_{8} as a New Template for High-Temperature Superconductivity at 110 K under 80 GPa.

The search for high-temperature superconducting superhydrides has recently moved into a new phase by going beyond extensively probed binary compounds and focusing on ternary ones with vastly expanded material types and configurations for property optimization. Theoretical and experimental works have revealed promising ternary compounds that superconduct at or above room temperature, but it remains a pressing challenge to synthesize stoichiometric ternary compounds with a well-resolved crystal structure that can host high-temperature superconductivity at submegabar pressures. Here, we report on the successful synthesis of ternary LaBeH_{8} obtained via compression in a diamond anvil cell under 110-130 GPa. X-ray diffraction unveils a rocksalt-like structure composing La and BeH_{8} units in the lattice. Transport measurements determined superconductivity with critical temperature T_{c} up to 110 K at 80 GPa, as evidenced by a sharp drop of resistivity to zero and a characteristic shift of T_{c} driven by a magnetic field. Our experiment establishes the first superconductive ternary compound with a resolved crystal structure. These findings raise the prospects of rational development of the class of high-T_{c} superhydrides among ternary compounds, opening greatly expanded and more diverse structural space for exploration and discovery of superhydrides with enhanced high-T_{c} superconductivity.

Giant enhancement of superconducting critical temperature in substitutional alloy (La,Ce)H9.

A sharp focus of current research on superconducting superhydrides is to raise their critical temperature Tc at moderate pressures. Here, we report a discovery of giant enhancement of Tc in CeH9 obtained via random substitution of half Ce by La, leading to equal-atomic (La,Ce)H9 alloy stabilized by maximum configurational entropy, containing the LaH9 unit that is unstable in pure compound form. The synthesized (La,Ce)H9 alloy exhibits Tc of 148-178 K in the pressure range of 97-172 GPa, representing up to 80% enhancement of Tc compared to pure CeH9 and showcasing the highest Tc at sub-megabar pressure among the known superhydrides. This work demonstrates substitutional alloying as a highly effective enabling tool for substantially enhancing Tc via atypical compositional modulation inside suitably selected host crystal. This optimal substitutional alloying approach opens a promising avenue for synthesis of high-entropy multinary superhydrides that may exhibit further increased Tc at even lower pressures.

Effect of Magnetic Impurities on Superconductivity in LaH10.

Polyhydrides are a novel class of superconducting materials with extremely high critical parameters, which is very promising for sensor applications. On the other hand, a complete experimental study of the best so far known superconductor, lanthanum superhydride LaH10 , encounters a serious complication because of the large upper critical magnetic field HC2 (0), exceeding 120-160 T. It is found that partial replacement of La atoms by magnetic Nd atoms results in significant suppression of superconductivity in LaH10 : each at% of Nd causes a decrease in TC by 10-11 K, helping to control the critical parameters of this compound. Strong pulsed magnetic fields up to 68 T are used to study the Hall effect, magnetoresistance, and the magnetic phase diagram of ternary metal polyhydrides for the first time. Surprisingly, (La,Nd)H10 demonstrates completely linear HC2 (T) âˆ |T - TC |, which calls into question the applicability of the Werthamer-Helfand-Hohenberg model for polyhydrides. The suppression of superconductivity in LaH10 by magnetic Nd atoms and the robustness of TC with respect to nonmagnetic impurities (e.g., Y, Al, C) under Anderson's theorem gives new experimental evidence of the isotropic (s-wave) character of conventional electron-phonon pairing in lanthanum decahydride.

Quantification of Eccentric Fixation Using Spectral-Domain Optical Coherence Tomography.

PURPOSE: This study aimed to evaluate the utility of optical coherence tomography (OCT) in the quantification of eccentric fixation in amblyopic patients. MATERIAL AND METHODS: In this study, 14 amblyopic patients and 10 healthy volunteers were enrolled. Under non-mydriatic conditions, fixation tests were performed directly using a fixation ophthalmoscope and indirectly using spectral-domain OCT. For evaluations using OCT, the distance between the fovea and the fixation point, which was determined by a cross-sectional image, was measured. RESULTS: On evaluations of healthy volunteers by OCT, the mean distance between the fixation point and the fovea was 80.4 ± 37.7 µm for the dominant eyes and 63.7 ± 36.4 µm for non-dominant eyes (p = 0.41). In amblyopic patients, on evaluation by OCT, the mean distance between the fixation point and the fovea was 193.8 ± 188.3 µm in amblyopic eyes and 83.5 ± 39.3 µm in paired fellow eyes (p = 0.02). Although OCT could detect eccentric fixation points in all the affected eyes of amblyopic patients, fixation ophthalmoscope was unable to quantify them in 2 of 14 affected eyes. CONCLUSIONS: Compared with a fixation ophthalmoscope, our method using OCT seems to be superior both in quantification and detection of eccentric fixation in amblyopic patients, without the need for mydriasis.

Emergence of double-dome superconductivity in ammoniated metal-doped FeSe.

The pressure dependence of the superconducting transition temperature (Tc) and unit cell metrics of tetragonal (NH3)yCs0.4FeSe were investigated in high pressures up to 41 GPa. The Tc decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The Tc vs. c plot is compared with those of various (NH3)yMxFeSe (M: metal atoms) materials exhibiting different Tc and c, showing that the Tc is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the Tc. No superconductivity was observed down to 4.3 K in (NH3)yCs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the Tc reaching 49 K at 21 GPa. The appearance of a new superconducting phase is not accompanied by a structural transition, as evidenced by pressure-dependent XRD. Furthermore, Tc slowly decreased with increasing pressure above 21 GPa, and at 41 GPa superconductivity disappeared entirely at temperatures above 4.9 K. The observation of a double-dome superconducting phase may provide a hint for pursuing the superconducting coupling-mechanism of ammoniated/non-ammoniated metal-doped FeSe.

Ca-VII: a chain ordered host-guest structure of calcium above 210 GPa.

The recently discovered high pressure phase VII of calcium [M. Sakata et al., Phys. Rev. B 83, 220512(R) (2011)] has the highest superconducting transition temperature (T(c)) of 29 K among all the elements. Understanding the cause for such a high T(c) state is necessary to clarify its crystal structure. The structure of this phase was determined by an x-ray powder diffraction experiment and a density functional theory calculation and was not found to be the usual host-guest type but consisted of a 2×2 supercell in the tetragonal ab plane with a commensurate host-guest ratio of 4/3 along the c axis containing 128 atoms.

Comparative study of FDG PET/CT and conventional imaging in the staging of rhabdomyosarcoma.

OBJECTIVE: The current study was conducted to compare the diagnostic accuracy between (18)F-fluoro-2-deoxy-D: -glucose (FDG) positron emission tomography (PET)/computed tomography (CT), and conventional imaging (CI) for the staging and re-staging of patients with rhabdomyosarcomas. METHODS: Thirty-five patients who underwent FDG PET/CT prior to treatment were evaluated retrospectively. CI methods consisted of (99m)Tc-hydroxymethylene diphosphonate bone scintigraphy, chest radiograph, whole body CT, and magnetic resonance imaging of the primary site. The images were reviewed and two boardcertified radiologists reached a diagnostic consensus. Tumor stage was confirmed by histological examination and/or follow-up examinations. RESULTS: Interpretation on the basis of FDG PET/CT, and CI, diagnostic accuracies of the T and N stages were similar. Using FDG PET/CT, the M stage was correctly assigned in 31 patients (89%), whereas the accuracy of CI in M stage was 63%. TNM stage was correctly assessed with FDG PET/CT in 30 of 35 patients (86%) and with CI in 19 of 35 patients (54%). The overall TNM staging and M staging accuracies of FDG PET/CT were significantly higher than that of CI (P < 0.01). CONCLUSIONS: FDG PET/CT is more accurate than CI regarding clinical staging and re-staging of patients with rhabdomyosarcomas.

Crystal structures of calcium IV and V under high pressure.

High-pressure phases IV and V of calcium discovered in 2005 have the highest superconducting transition temperature of 25 K among all the elements; however, their crystal structures have not been determined. From the x-ray powder diffraction data, both Ca IV and V have been found to form unique and complex structures with a coordination number of 7. They were confirmed to be identical to the theoretical models that were recently predicted [Ishikawa, Phys. Rev. B 77 020101(R) (2008)].