Generation of surface plasmons by electron beam excitation

We report on the first demonstration of excitation of propagating surface plasmon polaritons (SPPs) by injection of a beam of free electrons on an unstructured metal interface, providing a highly localized and intense source of plasmon waves. The plasmons were detected by a grating-assisted decoupling into light at a set of distances from the excitation point. This technique allows the high-resolution mapping of plasmon and photon emission from metal nanostructures

Premartensitic transition driven by magnetoelastic interaction in bcc ferromagnetic Ni2MnGaNi_{2}MnGa

We show that the magnetoelastic coupling between the magnetization and the amplitude of a short wavelength phonon enables the existence of a first order premartensitic transition from a bcc to a micromodulated phase in $Ni_{2}MnGa$. Such a magnetoelastic coupling has been experimentally evidenced by AC susceptibility and ultrasonic measurements under applied magnetic field. A latent heat around 9 J/mol has been measured using a highly sensitive calorimeter. This value is in very good agreement with the value predicted by a proposed model.Comment: 4 pages RevTex, 3 Postscript figures, to be published in Physical Review Letter

Intermediate phase in the spiral antiferromagnet Ba_2CuGe_2O_7

The magnetic compound Ba_2CuGe_2O_7 has recently been shown to be an essentially two-dimensional spiral antiferromagnet that exhibits an incommensurate-to-commensurate phase transition when a magnetic field applied along the c-axis exceeds a certain critical value H_c. The T=0 dynamics is described here in terms of a continuum field theory in the form of a nonlinear sigma model. We are thus in a position to carry out a complete calculation of the low-energy magnon spectrum for any strength of the applied field throughout the phase transition. In particular, our spin-wave analysis reveals field-induced instabilities at two distinct critical fields H_1 and H_2 such that H_1 < H_c < H_2. Hence we predict the existence of an intermediate phase whose detailed nature is also studied to some extent in the present paper.Comment: 15 pages, 11 figures, 2 table

Application of a wavelet technique for the detection of earthquake signatures in the geomagnetic field

We developed an algorithm especially adapted to <i>single-station </i>wavelet detection of geomagnetic events, which precede or accompany the earthquakes. The detection problem in this situation is complicated by a great variability of earthquakes and accompanied phenomena, which aggravates finding characteristic features of the events. Therefore we chose to search for the characteristic features of both &quot;disturbed&quot; intervals (containing earthquakes) and &quot;quiet&quot; recordings. In this paper we propose an algorithm for solving the problem of detecting the presence of signals produced by an earthquake via analysis of its signature against the existing database of magnetic signals. To achieve this purpose, we construct the magnetic signature of certain earthquakes using the distribution of the energies among blocks, which consist of wavelet packet coefficients