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| Issue 4, 2024 |
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Extracts from the Internet | ||
Spin Hall effect1 October 2006D.Awschalom and his colleagues from the University of California and Pennsylvania State University have detected the spin Hall effect at room temperature for the first time. The effect was observed in a nonmagnetic material in the absence of an external magnetic field and consisted in the fact that an electron spin flow developed perpendicular to the electric field direction - leading to a concentration difference between opposite spin electrons on the side faces of the sample. The reason for this phenomenon is that the scattering direction of an electron depends on precisely how the electron's spin is directed when participating in the spin- orbit interaction. The spin Hall effect was predicted by M.I.Dyakonov and V.I.Perel in 1971 and first discovered by D.Awschalom and his colleagues in their 2004 study on GaAs at 20K. In the new experiment, 1.5mk thick semiconducting films of chlorine-doped ZnSe were investigated using Kerr rotation spectroscopy. As the temperature increased from 10 to 295K, the size of the spin Hall effect (i. e., side face spin polarization) decreased by about ten times while still remaining measurable. The task for future research is to increase the spin coherence time and the fraction of polarized electrons at elevated temperatures. The spin Hall effect can find applications in designing spin current sources for spintronic devices. Source: Phys. Rev. Lett. 97 126603 (2006) Quantum cooling1 October 2006Measuring the quantum state of a system always exerts a perturbing effect on the system. Now an experiment on the practical use of this effect for cooling a microscopic beam has been performed at the University of Maryland. In the experiment, use was made of the fact the mechanical vibration amplitude of the beam could be put into correspondence with a certain effective temperature. Close to the beam, the team placed a superconducting single-electron transistor, the electromagnetic field in which depended on (and thus allowed measurement of) the level of vibrations in the beam. This quantum measurement led in some cases to smaller vibration amplitudes and thus to the cooling of the beam. The cooling obtained in the experiment was from 550 to 300K. The reason for the cooling lies in the asymmetric spectrum of the transistor's quantum noises that exert back-action on the beam being measured. It is believed that this method of cooling may in the future be useful for nanoelectronics device applications. Source: Nature 443 123 (2006) Superconducting qubits1 October 2006M.Steffen and his colleagues from the University of California at Santa Barbara have for the first time obtained a quantum-correlated (entangled) state of two superconducting Josephson tunnelling junctions. The researchers used the method of `quantum tomography' when performing the measurement of the quantum state of the system that confirmed the appearance of an entangled state. Because superconducting elements can store quantum bits (qubits) of information, creating coherent systems of superconducting elements is promising for the development of quantum computers. In one of the alternative approaches, as many as eight ions in an atomic trap were brought into an entangled state. Thus far, no difficulties of principle are known which would prevent creating similar entangled states in systems of more than two superconducting elements. Source: http://physicsweb.org/articles/news/10/9/3/1 Superhigh frequency nanotube resonators1 October 2006Researchers from Lawrence Berkeley National Laboratory and the University of California report creating a nanoelectromechanical resonator based on a carbon nanotube. The nanotube is attached to two metallic contacts 300nm apart, by means of which a high frequency alternating current is passed through the nanotube, and at a distance of 200nm from the tube, a third (gate) contact is placed, to which a signal of a different frequency is applied. While the electric field of the gate exerts a force on the nanotube, the vibrations of the nanotube, in turn, change the capacity between itself and the gate. All the contacts are connected to a radio scheme, which measures the amplitude and phase of the vibrations. At room temperature and an air pressure of 1atm., a resonance occurs between the mechanical vibrations of the tube and the electromagnetic oscillations at about 1.3GHz. That this frequency is somewhat lower than in vacuum is due to the air molecules depositing themselves on the nanotube surface. The dependence of the resonant frequency on the deposited mass allowed supersmall masses (10-18g) to be measured. The effective quality of the resonator reached Q=440. Source: Phys. Rev. Lett. 97 087203 (2006) Testing general relativity1 October 2006Of all currently known systems for probing the effects of general relativity, there are a number of reasons why the double pulsar PSR J0737-3039A/B is the most promising: both neutron stars (A and B) are observed as radio pulsars, the pair is relatively close to the Sun (500pc), and the orbital period is only 2.4 hours - leading to large orbital velocities and orbital accelerations and allowing an independent determination of the mass ratio of the stars. PSR J0737-3039A/B has been studied by several telescopes since its discovery 2.5 years ago. By observing the shape and spacing of the radio pulses from the pulsar, it proved possible to study such effects as orbit shrinking due to gravitational wave emission by the system; non-Keplerian corrections due to spacetime curvature; and the effect of gravitational field on signal propagation. All in all, a test of general relativity theory was carried out at 105 times solar system's gravitational field to within 0.005% - a record high accuracy for the high field range. Source: astro-ph/0609417 |
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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