Goldstone-Mode Phonon Dynamics in the Pyrochlore Cd2Re2O7

We have measured the polarized Raman scattering spectra of Cd2Re2O7, the first superconducting pyrochlore, as a function of temperature. For temperatures below the cubic-to-tetragonal structural phase transition (SPT) at 200K, a peak with B1 symmetry develops at zero frequency with divergent intensity. We identify this peak as the first observation of the Goldstone phonon in a crystalline solid. The Goldstone phonon is a collective excitation that exists due to the breaking of the continuous symmetry with the SPT. Its emergence coincides with that of a Raman-active soft mode. The order parameter for both features derives from an unstable doubly-degenerate vibration (with Eu symmetry) of the O1 atoms which drives the SPT.Comment: 4+ pages, 4 figures. Updated figures and text. Accepted to PR

An investigation of the parametric X-ray along the velocity of emitting particle

Parametric X-rays (PXR) along the velocity of relativistic electrons crossing a crystalline target is studied in this work. The detailed theory of PXRfor Laue scattering geometry is developed with account of contributions of both PXRand transition radiation (TR) to the total emission yield. An influence of photoabsorption and interference between PXRand TRon the forward PXR properties are studied. Most appropriate conditions for the real experiment devoted to forward PXRobservation are elucidated on the basis of the developed theory. The advantage of the use of heavy crystals with this aim in mind is shown. The expected experimental results are discussedyesBelgorod State Universit

On the effect of anomalous photoabsorption in parametric X radiation

The parametric X radiation of relativistic electrons passing through a monocrystal is considered. It is demonstrated that, contrary to widespread option, conditions for the effect of anomalous photoabsorption to show up can be realized in the Laue scattering geometryye

Role of the Dzyaloshinskii-Moriya interaction in multiferroic perovskites

With the perovskite multiferroic RMnO3 (R = Gd, Tb, Dy) as guidance, we argue that the Dzyaloshinskii-Moriya interaction (DMI) provides the microscopic mechanism for the coexistence and strong coupling between ferroelectricity and incommensurate magnetism. We use Monte-Carlo simulations and zero temperature exact calculations to study a model incorporating the double-exchange, superexchange, Jahn-Teller and DMI terms. The phase diagram contains a multiferroic phase between A and E antiferromagnetic phases, in excellent agreement with experiments.Comment: 6 pages, 5 figure

НВЧ аплікатор для гіпертермії на основі спіральної періодичної структури

The use of periodic structures for creation of applicators with the homogeneous or near to him distributing of the electromagnetic field is offered. The given results of modeling of the offered structure and the numerical accounts show prospects of such applicators.Предложено использование периодических структур для создания аппликаторов с однородным или близким к нему распределением электромагнитного поля. Результаты моделирования и числовые расчёты показывают перспективность таких аппликаторов.Запропоновано використання періодичних структур для створення аплікаторів з однорідним або близьким до нього розподілом електромагнітного поля. Наведені результати моделювання запропонованої структури та числові розрахунки показують перспективність аплікаторів такого типу

Полярные сияния в каспе и его приполюсной окрестности: исследование отдельного события

Summary We present a case study of the dayside aurora observed simultaneously with optical instruments from the ground and with auroral particle spectrometers aboard the DMSP F16 and F17 satellites. Optical observations were carried out with an all-sky camera at the Polar Geophysical Institute (PGI) observatory Barentsburg on Svalbard. The aurora as a whole moved equatorward in response to negative turning of the IMF Bz component and then the distinct faint rayed arc intensified, moved to the north and faded. Satellite DMSP F17 crossed the cusp twenty minutes after Bz turned southward. Joint analysis of optical and satellite data showed that faint auroral structures are embedded into the cusp precipitations and correspond to the bursts of electron precipitations with energy below 100 eV. The next satellite crossed the camera field-of-view ten minutes later and the data showed that the source of the faded poleward moving rayed arc was located, most probably, on the non-closed magnetic field lines. This finding and the presence of ion-energy dispersion in the DMSP data allows us to make the conclusion that the dayside reconnection may be considered as the reason for this kind of aurora activity. In this study we also estimated the altitude and horizontal scale of auroral rays in the cusp.Исследован редкий случай одновременной регистрации дневных полярных сияний наземной оптической аппаратурой и детектором высыпающихся частиц на спутниках DMSP F16 и F17. Оптические измерения проводились камерой полного обзора неба Полярного геофизического института, установленной в обсерватории Баренцбург на арх. Шпицберген. Следуя развороту вертикальной компоненты межпланетного магнитного поля (Bz-компоненты ММП) в область отрицательных значений, система слабых лучистых дуг сместилась к югу, после чего одна из дуг начала дрейфовать обратно к полюсу и пропала. Спутник DMSP F17 пересек касп спустя двадцать минут после разворота Bz-компоненты. Совместный анализ оптических и спутниковых данных показал, что наблюдаемые слабые лучистые структуры находятся в области каспенных высыпаний и пространственно связаны с всплеском высыпающихся электронов с энергией менее 100 эВ. Следующий спутник DMSP пересек поле  зрения камеры спустя десять минут после первого,  и анализ его данных показал, что эта дуга в момент исчезновения находилась в области разомкнутых силовых линий. Этот результат, дополненный специфической формой протонных высыпаний в данных спутника DMSP, которую традиционно связывают с пересоединением, позволил нам прийти к выводу, что смещавшаяся к полюсу слабая лучистая дуга могла представлять собой ионосферный след только что пересоединившейся магнитной силовой трубки, уносимой солнечным ветром в антисолнечном направлении. Оценена высота и поперечный размер элемента лучистой структуры в каспе

Metallic "Ferroelectricity" in the Pyrochlore Cd2Re2O7

A class of materials known as ``ferroelectric metals'' was discussed theoretically by Anderson and Blount in 1965 [Phys. Rev. Lett. 14, 217 (1965)], but to date no examples of this class have been reported. Here we present measurements of the elastic moduli of Cd2Re2O7 through the 200 K cubic-to-tetragonal phase transition. A Landau analysis of the moduli reveals that the transition is consistent with Cd2Re2O7 being classified as a ``ferroelectric metal'' in the weaker sense described by Anderson and Blount (loss of a center of symmetry). First-principles calculations of the lattice instabilities indicate that the dominant lattice instability corresponds to a two-fold degenerate mode with Eu symmetry, and that motions of the O ions forming the O octahedra dominate the energetics of the transition.Comment: 4 pages, 2 figure

Improvement of Adhesion of the Wheels of the Railway Carriage to the Rails by Means of Supply of the Scale and Magnetite Particles to the Contact Zone

The article proposes a method to improve adhesion of the wheels to the rails of the railway carriage by means of supply of abrasive loose materials as an alternative to quartz sand to the zone of their contact: metal scale (Fe₃O₄ ) being the waste of rolling and forging, as well as the iron oxide—magnetite (FeO·Fe₂O₃) of the natural origin. The comparative assessment of efficiency of use of scale and magnetite was carried out in relation to quartz sand traditionally used for railway transport. The adhesion coefficient and wear intensity are used as comparison criteria

Angular dependence of the coherent peak position in the polarization bremsstrahlung spectrum of relativistic electrons in polycrystalline targets

The spectra of the polarization bremsstrahlung (PB) in the X-ray range induced by 7-MeV electrons in polycrystalline Al, Cu, and Ni polycrystalline films have been measured and the angular dependences of the PB characteristics have been studiedyesBelgorod State Universit