Probing confined interfacial excitations in buried layers by Brillouin light scattering

Brillouin light scattering from silicon oxynitride films grown on GaAs reveals a low frequency elastic wave excitation at frequencies lying below that of the Rayleigh surface wave. This mode, identified as an excitation localized by the interface, arises from the presence of a soft, thin transition layer between the film and substrate. Observations of this low frequency excitation offer a previously unexplored approach to characterize, non-destructively, the properties of buried interfaces.Comment: 4 pages, 4 figures, key words: interface, interfacial waves, guided acoustic waves, acoustic waveguid

Magnetic imaging of layer-by-layer reversal in Co/Pt multilayers with perpendicular anisotropy

For very thin Co layers, the exchange coupling between adjacent Co layers in Co∕Pt multilayers is ferromagnetic and the coupling strength varies nonmonotonically as the nonmagnetic Pt layer thickness (t_Pt) ranges from 3 to 75 Å. We report on the magnetization reversal process in a series of [Co(4 Å)/Pt(t_Pt)]_N multilayers observed by magneto-optical Kerr microscopy as a function of t_Pt and layer repetition N. The images reveal the evolution of magnetic reversal processes that strongly depend on t_Pt and therefore on the interlayer coupling. For Co/Pt multilayers with small t_Pt, e.g., 11 Å, where the Co layers are strongly coupled, the whole multilayer switches as a single ferromagnet. As Co layers are separated farther and become weakly coupled, e.g., at t_Pt=41 Å, layer-by-layer magnetic reversal is observed. The Kerr images reveal metastable magnetic domain configurations during layer-by-layer switching which is not evident in the measured hysteresis loops during the abrupt magnetic reversal for Co∕Pt multilayers with weak interlayer coupling at large t_Pt

Magnetic Wire Traps and Programmable Manipulation of Biological Cells

We present a multiplex method, based on microscopic programmable magnetic traps in zigzag wires patterned on a platform, to simultaneously apply directed forces on multiple fluid-borne cells or biologically inert magnetic microparticles or nanoparticles. The gentle tunable forces do not produce damage and retain cell viability. The technique is demonstrated with T-lymphocyte cells remotely manipulated (by a joystick) along desired trajectories on a silicon surface with average speeds up to 20 μm/s

Dispersive Gap Mode of Phonons in Anisotropic Superconductors

We estimate the effect of the superconducting gap anisotropy in the dispersive gap mode of phonons, which is observed by the neutron scattering on borocarbide superconductors. We numerically analyze the phonon spectrum considering the electron-phonon coupling, and examine contributions coming from the gap suppression and the sign change of the pairing function on the Fermi surface. When the sign of the pairing function is changed by the nesting translation, the gap mode does not appear. We also discuss the suppression of the phonon softening of the Kohn anomaly due to the onset of superconductivity. We demonstrate that observation of the gap dispersive mode is useful for sorting out the underlying superconducting pairing function.Comment: 7 pages, 12 figures, to be published in J. Phys. Soc. Jp

Many-body correlations probed by plasmon-enhanced drag measurements in double quantum well structures

Electron drag measurements of electron-electron scattering rates performed close to the Fermi temperature are reported. While evidence of an enhancement due to plasmons, as was recently predicted [K. Flensberg and B. Y.-K. Hu, Phys. Rev. Lett. 73, 3572 (1994)], is found, important differences with the random-phase approximation based calculations are observed. Although static correlation effects likely account for part of this difference, it is argued that correlation-induced multiparticle excitations must be included to account for the magnitude of the rates and observed density dependences.Comment: 4 pages, 3 figures, revtex Accepted in Phys. Rev.

Nano/micro-scale magnetophoretic devices for biomedical applications

In recent years there have been tremendous advances in the versatility of magnetic shuttle technology using nano/micro-scale magnets for digital magnetophoresis. While the technology has been used for a wide variety of single-cell manipulation tasks such as selection, capture, transport, encapsulation, transfection, or lysing of magnetically labeled and unlabeled cells, it has also expanded to include parallel actuation and study of multiple bio-entities. The use of nano/micro-patterned magnetic structures that enable remote control of the applied forces has greatly facilitated integration of the technology with microfluidics, thereby fostering applications in the biomedical arena. The basic design and fabrication of various scaled magnets for remote manipulation of individual and multiple beads/cells, and their associated energies and forces that underlie the broad functionalities of this approach, are presented. One of the most useful features enabled by such advanced integrated engineering is the capacity to remotely tune the magnetic field gradient and energy landscape, permitting such multipurpose shuttles to be implemented within lab-on-chip platforms for a wide range of applications at the intersection of cellular biology and biotechnology. © 2016 IOP Publishing Ltd.

RAMAN SPECTRA OF SOLID MOLECULAR NITROGEN

($^{\ast}$) Laboratoire d'Infrarouge, Associ\'e au CNRS, B$\hat{a}t.$ 350, Universit\'e Paris XI, 91405 ORSAY-C\'edex, FRANCE. ($^{\ast\ast}$) Dept. of Physics, Ohio State University, 174 West, 18th Avenue, Columbus Ohio, 43210, USA. ($^{\ast\ast\ast}$) Dept. of Physics and Astronomy, The University of Alabama, Tuscaloosa Alabama, 35487, USA.Author Institution: Laboratoire d'Infrarouge, Associ\'e CNRS, B$\hat{a}t$ 350, Universit\'e; Dept. of Physics, Ohio State University; Dept. of Physics and Astronomy, The University of AlabamaDue to the simpler geometrical arrangement, the theoretical interpretation of molecular interactions may be easier in the lattice than in the gas phase. In the case of the nitrogen molecule, the structure of the solid at normal pressure is known. A phase transition occurs at a temperature $T_{ph} = 35.6K$. The crystal is cubic $(\alpha-N_{2}$ ) for $T T_{ph}$. This paper reports preliminary results of a Raman scattering study on single crystal $N_{2}$. The experiment is specifically designed to investigate the effect of the above structural phase transition on the molecular and phonon excitations. The crystal $(4\times 2 \times 2 cm)$ is grown in a cryostat where the temperature is servo controlled over a large domain by appropriate heating of a flow of gaseous helium. The spectra are excited with a krypton laser and the scattered beam recorded with a spectral resolution equal to about $1 cm^{-1}$. The crystal cell, the optical system to enhance the signal to noise ratio and the growth technique are also described