Calibration of a Pt resistance thermometer (Netsushin) in magnetic fields and under pressure in the range of 1.5–300 K and below 1.5 GPa is presented. With the pressure medium, olefin olygomers, Daphne 7373, the pressure is continuous at its solidification and the pressure drop from 300 to 4.2 K by 0.15–0.17 GPa is constant, irrespective of the initial clamped pressure at 300 K. The applicability of the thermometer and the medium for precise study in field and pressure at low temperature is discussed.
We present a precision analysis of the 136 Xe two-neutrino ββ electron spectrum above 0.8 MeV, based on highstatistics data obtained with the KamLAND-Zen experiment. An improved formalism for the two-neutrino ββ rate allows us to measure the ratio of the leading and subleading 2νββ nuclear matrix elements (NMEs), ξ 2ν 31 ¼ −0.26 þ0.31 −0.25. Theoretical predictions from the nuclear shell model and the majority of the quasiparticle random-phase approximation (QRPA) calculations are consistent with the experimental limit. However, part of the ξ 2ν 31 range allowed by the QRPA is excluded by the present measurement at the 90% confidence level. Our analysis reveals that predicted ξ 2ν 31 values are sensitive to the quenching of NMEs and the competing contributions from low-and high-energy states in the intermediate nucleus. Because these aspects are also at play in neutrinoless ββ decay, ξ 2ν 31 provides new insights toward reliable neutrinoless ββ NMEs.
A novel scheme for the focusing of high-energy leptons in future linear colliders was proposed in 2001 [P. Raimondi and A. Seryi, Phys. Rev. Lett. 86, 3779 (2001)]. This scheme has many advantageous properties over previously studied focusing schemes, including being significantly shorter for a given energy and having a significantly better energy bandwidth. Experimental results from the ATF2 accelerator at KEK are presented that validate the operating principle of such a scheme by demonstrating the demagnification of a 1.3 GeV electron beam down to below 65 nm in height using an energy-scaled version of the compact focusing optics designed for the ILC collider.
The suppression of superconductivity by nonmagnetic disorder is investigated systematically in the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2. We introduce a nonmagnetic disorder arising from molecule substitution in part with deuterated BEDT-TTF or BMDT-TTF for BEDT-TTF molecules and molecular defects introduced by X-ray irradiation. A quantitative evaluation of the scattering time τ dHvA is carried out by de Haas-van Alphen (dHvA) effect measurement. A large reduction in Tc with a linear dependence on 1/τ dHvA is found in the small-disorder region below 1/τ dHvA ≃ 1 × 10 12 s −1 in both the BMDT-TTF moleculesubstituted and X-ray-irradiated samples. The observed linear relation between Tc and 1/τ dHvA is in agreement with the Abrikosov-Gorkov (AG) formula, at least in the small-disorder region. This observation is reasonably consistent with the unconventional superconductivity proposed thus far for the present organic superconductor. A deviation from the AG formula, however, is observed in the large-disorder region above 1/τ dHvA ≃ 1 × 10 12 s −1 , which reproduces the previous transport study (J. G. Analytis et al.: Phys. Rev. Lett. 96 (2006) 177002). We present some interpretations of this deviation from the viewpoints of superconductivity and the inherent difficulties in the evaluation of scattering time.
We investigated the propagation of the threading dislocations in the GaN layer grown by facet-controlled epitaxial lateral overgrowth (FACELO). The mixed-type dislocations were bent toward the mask areas and they were terminated at the voids on the SiO2 masks. On the other hand, the pure edge dislocations were bent in the direction of the mask stripe. No dislocations originating from the GaN/sapphire interface propagated to the surface. As a result, it was confirmed that a large reduction of dislocation density was achieved. Therefore, FACELO seems to be a promising technique for the realization of a GaN wafer of low dislocation density.
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