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Issue 12, 2024
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Extracts from the Internet


Direct observation of the Landau levels

Ê. Hashimoto (Tohoku University, Japan) and colleagues were able to observe for the first time the spatial structure of electron wave functions corresponding to the Landau levels using scanning tunneling spectroscopy. Landau levels are the energy levels of quantized motion of electrons across the magnetic field. They studied two-dimensional electron gas in the surface layer of semiconducting InSb. The measurements were performed at 0.3 K in 6 T magnetic field under high vacuum conditions. Fourier analysis of the spectroscopic data made it possible to identify several oscillations of the radial wave functions of electrons for each Landau level. In some cases, the structure of the wave functions was also discernible in the real space, shaped into one, two or three concentric rings, although observation of oscillations of wave functions in real space is much more complicated due to the drift and chaotic motions of the centers of electron orbitals. The results of these studies are important, among other things, for applications of the quantum Hall effect. Source: Phys. Rev. Lett. 109 116805 (2012)

The impact of ions on the surface

The properties of surface defects on CaF2 arising from collisions with this surface of slow multiply charged Xeq+ ions, where the ion charge q in the experiment was varied from 10 to 33, were studied at the Helmholtz Dresden--Rossendorf Centre (Germany). The surface topography was investigated using the atomic force microscope. It was possible to establish the conditions under which specific types of defects arise and construct the “phase diagram” of how they form depending on the kinetic energy of ions and their charges. It was found that at low q an ion can cause the formation of a cluster of defects in such a way that the surface remains even nonetheless. The presence of a cluster of triangular shape (due to the configuration of the crystal lattice) became noticeable only after chemical etching of the surface. If q was sufficiently high, nanoscale hillocks would form on the surface in addition to defect clusters; the hillocks were visible even without etching. This growth of hillocks is caused by melting of the crystal lattice around the ion that penetrated into the subsurface layers, by excitation and ejection of atoms. The position of the hillocks on the “phase diagram” mainly depends on the ion charge and only very weakly on ions' kinetic energy. However, the boundary of the area in which triangular defects are visible after etching depends essentially on both these parameters. Source: Phys. Rev. Lett. 109 117602 (2012)

Magnetic anisotropy of the complexes Fe4

Å. Burzuri et al. (Delft University of Technology, The Netherlands) investigated the magnetic anisotropy of single-molecule Fe4 complexes consisting of four iron atoms embedded in a non-magnetic organic molecule. The complexes were placed between three gold electrodes in the FET configuration. A Fe4 complex could capture electrons and the resulting electronic states could be measured by applying a potential to the gate electrode. The magnetic properties of Fe4 varied significantly from one electron state to another. The current-voltage characteristic of the system was built depending on the electron state of the Fe4 complex, the external magnetic field and the orientation of Fe4 relative to the direction of the magnetic field. The resulting dependence proved to be nonlinear in a certain range of parameters, pointing to the magnetic anisotropy of Fe4 complexes. Source: Phys. Rev. Lett. 109 147203 (2012)

Plasma in spheromak

A team of researchers at the University of Washington led by T.R. Jarboe conducted experiments on stable injection of plasma into improved spheromak — a device for self-confinement of plasma by the magnetic field it carries. Spheromaks may find applications in thermonuclear fusion energy production. They are not only of interest as such but can also be used as auxiliary systems for the injection of plasma into tokamaks. The installation consists of the central toroidal chamber incorporating two additional semi-toroidal “mug handles”. Plasma with self-twisted magnetic field (magnetic helicity) is injected into these handles. This geometry produces a configuration of electric currents and magnetic fields capable of containing plasma without external magnetic field, and such that its power requirements are two orders of magnitude lower than for magnetic confinement. The experiment reported threefold increase in electric current in the plasma, up to more than 40 kA. The designed facility is merely a prototype: the experiment has shown good results but under conditions far less demanding than the real conditions in a thermonuclear fusion reactor. Larger-scale studies will be required for more complete assessment of the effectiveness and feasibility of this technique. Source: University of Washington

“Lost baryons” in the Galaxy

Observations with space x-ray telescopes of the environment around the Galaxy discovered a massive halo of hot gas which perhaps contains the so-called “lost baryons”. The problem of “lost baryons” lies in the fact that direct observations identified only about a half of the amount of baryonic matter that was produced in the Universe by the primeval nucleosynthesis and that is implied by the observations of anisotropy of the primeaval microwave background. A. Gupta (University of Ohio, United States) et al. studied non-shifted (having z = 0) absorption lines of oxygen ions in the emission of eight active galactic nuclei observed by the Chandra X-ray Observatory. The character of lines is such that they appear to arise when radiation passes through the gas halo of greater than 100 kps radius and temperature of 1-2.5 million K. This halo envelops the mass comparable with that of all starts in the Galactic disk. It may comprise even the entire local group of galaxies. In addition, Gupta et al used the data from the telescopes XMM-Newton and Suzaku which recorded the emission from gases in the halo, allowing more accurate calculation of the mass of hot gas. Earlier observations by the Hubble Space Telescope already indicated that such massive hot gas halos do exist around very distant galaxies observed in the early universe. Source: Astrophys. J. Lett. 756 L8 (2012)

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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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