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| Issue 4, 2024 |
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Extracts from the Internet | ||
Anisotropic Ginzburg-Landau theory for the Ca0.8La0.2Fe0.98Co0.02As2 crystal1 October 2016Iron-based superconductors containing calcium or rare-earth elements possess a number of interesting properties, but their examination was earlier obstructed because of the absence of high-quality single crystals. High-quality 2×1×0.05 mm3 Ca0.8La0.2Fe0.98Co0.02As2 crystals were synthesized by X. Xing (Southwest University, Nanjing, Chinese People's Republic) and colleagues through a slow heating and cooling of a mixture of substances in a quartz tube. This superconductor proved to have a high critical current of 2×106 A cm-2 at a temperature of 5 K. The second peak on the hysteresis loop and the anisotropy of the upper critical field were investigated by varying the magnitude and direction of the external magnetic field. The upper field scaling was described by generalization of the Ginzburg – Landau theory undertaken by G. Blatter, V.B. Geshkenbein and A.I. Larkin (see Phys. Rev. Lett. 68 875 (1992)). The study of the normal state of Ca0.8La0.2Fe0.98Co0.02As2 has shown a nonmonotonic temperature dependence of the Hall coefficient with minimum at a temperature T≈175 K below which the Kohler’s rule is violated. Source: Supercond. Sci. Technol. 29 055005 (2016) Superconductivity in NbN nanowires1 October 2016K.Yu. Arutyunov (Moscow Institute of Electronics and Mathematics and P.L. Kapitza Institute for Physical Problems, Russia) with colleagues manufactured a set of NbN nanowires with different transverse sizes smaller than the superconducting coherence length and examined their electric properties. The measurements have shown that the critical current Tc follows the classical Ginzburg – Landau prediction for quasi-one-dimensional channel, Ic ∝ (1-T/Tc)3/2, and the temperature dependence of the resistance R(T) is indicative of the decisive role of the phase slip effect due to thermal fluctuations with a possible small contribution of the phase slip quantum effect (on account of quantum fluctuations). The intrinsic electronic inhomogeneities in the examined nanowires are either absent or have no significant effect on conductivity. Similar investigations of inhomogeneities in thin NbN films were earlier hampered by the shunting of some conducting film areas by other conducting areas. Source: arXiv:1602.07932 [cond-mat.supr-con] Anomalous Doppler effect in Bose-Einstein condensate1 October 2016The researchers from Germany and Italy J. Marino, A. Recati, and I. Carusotto have grounded the idea of the experiment aimed at studying analogs of some quantum effects. Proposed is observation of the atomic motion in Bose-Einstein condensate with a supersonic velocity in the condensate. Given this, the anomalous Doppler effect must take place, which was discussed by V.L. Ginzburg and colleagues (see, e.g., V.L. Ginzburg and V.P. Frolov, JETP Letters 43 339 (1986)), that is, transitions will proceed from lower to higher atomic electron levels and radiation (photons) will be emitted and the energy for transitions and radiation in this process will be drawn from the kinetic energy of the translational motion of the atom. Furthermore, an analog of the Casimir effect and quantum friction will be observed. It is proposed that as a particular realization the motion of 6Li atoms in Bose-Einstein condensate of 7Li atoms should be investigated and the transitions between the levels of hyper-fine splitting should be observed. Source: arXiv:1605.07642 [cond-mat.quant-gas] The existence of diphoton resonance at 750 GeV has not been confirmed1 October 2016The ATLAS and CMS collaborations operating at Large Hadron Collider have recently reported the observation of an unusual diphoton resonance at an energy of 750 GeV with statistical significance of ≈2-4 σ. Many hypotheses were put forward with possible explanations of this resonance, for example, the existence of new particles. However, according to the new data obtained in the same ATLAS and CMS experiments in 2016 at a pp-collision energy of 13 TeV the existence of the indicated resonance was not confirmed. No statistically significant excess over that predicted by the Standard Model was observed. This result in combination with the data obtained earlier at 8 TeV imposes restrictions on the parameters of some models involving the “new physics”. In particular, the now most stringent restrictions were obtained on the parameters of gravitons in the Randall-Sundrum theory that might split into two photons. Source: arXiv:1609.02507 [hep-ex] Black holes in a globular cluster1 October 2016When observing the radial distribution of stars in the globular cluster NGC 6101 E. Dalessandro (University of Bologna, Italy) with colleagues arrived at the conclusion that this cluster does not show mass segregation (concentration of more massive stars closer to the cluster center) that would have certainly occurred since the instant of its formation. M. Peuten and his colleagues from the University of Surrey (Great Britain) carried out computer simulation of cluster dynamics to establish that this contradiction can be eliminated by assuming a rather large fraction (≈1 %) of the whole cluster mass to exist in the form of stellar-mass black holes. The presence of a black hole with an intermediate mass of ≈103M☉ in the center of NGC 6101 is discussed as an alternative explanation. In his paper “What problems of physics and astrophysics seem now to be especially important and interesting” (see Phys. Usp. 42 353(1999)) V.L. Ginzburg referred the physics of black holes to most topical subjects in astrophysics. Source: Mon. Not. Roy. Astron. Soc. 462 2333 (2016) |
The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) — the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics. Permanent editor is Yu.N. Eroshenko. It is compiled from a multitude of Internet sources. | |
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