Localized ferromagnetic resonance force microscopy in permalloy-cobalt films

We report Ferromagnetic Resonance Force Microscopy (FMRFM) experiments on a justaposed continuous films of permalloy and cobalt. Our studies demonstrate the capability of FMRFM to perform local spectroscopy of different ferromagnetic materials. Theoretical analysis of the uniform resonance mode near the edge of the film agrees quantitatively with experimental data. Our experiments demonstrate the micron scale lateral resolution in determining local magnetic properties in continuous ferromagnetic samples.Comment: 7 pages, 3 figure

Mapping local optical densities of states in silicon photonic structures with nanoscale electron spectroscopy

Relativistic electrons in a structured medium generate radiative losses such as Cherenkov and transition radiation that act as a virtual light source, coupling to the photonic densities of states. The effect is most pronounced when the imaginary part of the dielectric function is zero, a regime where in a non-retarded treatment no loss or coupling can occur. Maps of the resultant energy losses as a sub-5nm electron probe scans across finite waveguide structures reveal spatial distributions of optical modes in a spectral domain ranging from near-infrared to far ultraviolet.Comment: 18 pages, 4 figure

Phase Transitions in the Two-Dimensional XY Model with Random Phases: a Monte Carlo Study

We study the two-dimensional XY model with quenched random phases by Monte Carlo simulation and finite-size scaling analysis. We determine the phase diagram of the model and study its critical behavior as a function of disorder and temperature. If the strength of the randomness is less than a critical value, $\sigma_{c}$, the system has a Kosterlitz-Thouless (KT) phase transition from the paramagnetic phase to a state with quasi-long-range order. Our data suggest that the latter exists down to T=0 in contradiction with theories that predict the appearance of a low-temperature reentrant phase. At the critical disorder $T_{KT}\rightarrow 0$ and for $\sigma > \sigma_{c}$ there is no quasi-ordered phase. At zero temperature there is a phase transition between two different glassy states at $\sigma_{c}$. The functional dependence of the correlation length on $\sigma$ suggests that this transition corresponds to the disorder-driven unbinding of vortex pairs.Comment: LaTex file and 18 figure

The Field-Tuned Superconductor-Insulator Transition with and without Current Bias

The magnetic-field-tuned superconductor-insulator transition has been studied in ultrathin Beryllium films quench-condensed near 20 K. In the zero-current limit, a finite-size scaling analysis yields the scaling exponent product vz = 1.35 +/- 0.10 and a critical sheet resistance R_{c} of about 1.2R_{Q}, with R_{Q} = h/4e^{2}. However, in the presence of dc bias currents that are smaller than the zero-field critical currents, vz becomes 0.75 +/- 0.10. This new set of exponents suggests that the field-tuned transitions with and without dc bias currents belong to different universality classes.Comment: RevTex 4 pages, 4 figures, and 1 table minor change

Can Short-Range Interactions Mediate a Bose Metal Phase in 2D?

We show here based on a 1-loop scaling analysis that short-range interactions are strongly irrelevant perturbations near the insulator-superconductor (IST) quantum critical point. The lack of any proof that short-range interactions mediate physics which is present only in strong coupling leads us to conclude that short-range interactions are strictly irrelevant near the IST quantum critical point. Hence, we argue that no new physics, such as the formation of a uniform Bose metal phase can arise from an interplay between on-site and nearest-neighbour interactions.Comment: 3 pages, 1 .eps file. SUbmitted to Phys. Rev.

24^{24}Mg(pp, α\alpha)21^{21}Na reaction study for spectroscopy of 21^{21}Na

The $^{24}$Mg($p$, $\alpha$)$^{21}$Na reaction was measured at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory in order to better constrain spins and parities of energy levels in $^{21}$Na for the astrophysically important $^{17}$F($\alpha, p$)$^{20}$Ne reaction rate calculation. 31 MeV proton beams from the 25-MV tandem accelerator and enriched $^{24}$Mg solid targets were used. Recoiling $^{4}$He particles from the $^{24}$Mg($p$, $\alpha$)$^{21}$Na reaction were detected by a highly segmented silicon detector array which measured the yields of $^{4}$He particles over a range of angles simultaneously. A new level at 6661 $\pm$ 5 keV was observed in the present work. The extracted angular distributions for the first four levels of $^{21}$Na and Distorted Wave Born Approximation (DWBA) calculations were compared to verify and extract angular momentum transfer.Comment: 11 pages, 6 figures, proceedings of the 18th International Conference on Accelerators and Beam Utilization (ICABU2014

Dispersity-Driven Melting Transition in Two Dimensional Solids

We perform extensive simulations of $10^4$ Lennard-Jones particles to study the effect of particle size dispersity on the thermodynamic stability of two-dimensional solids. We find a novel phase diagram in the dispersity-density parameter space. We observe that for large values of the density there is a threshold value of the size dispersity above which the solid melts to a liquid along a line of first order phase transitions. For smaller values of density, our results are consistent with the presence of an intermediate hexatic phase. Further, these findings support the possibility of a multicritical point in the dispersity-density parameter space.Comment: In revtex format, 4 pages, 6 postscript figures. Submitted to PR

Constellations of identity: place-ma(r)king beyond heritage

This paper will critically consider the different ways in which history and belonging have been treated in artworks situated in the Citadel development in Ayr on the West coast of Scotland. It will focus upon one artwork, Constellation by Stephen Hurrel, as an alternative to the more conventional landscapes of heritage which are adjacent, to examine the relationship between personal history and place history and argue the primacy of participatory process in the creation of place and any artwork therein. Through his artwork, Hurrel has attempted to adopt a material process through which place can be created performatively but, in part due to its non-representational form, proves problematic, aesthetically and longitudinally, in wholly engaging the community. The paper will suggest that through variants of ‘new genre public art’ such as this, personal and place histories can be actively re-created through the redevelopment of contemporary urban landscapes but also highlight the complexities and indeterminacies involved in the relationship between artwork, people and place

Freezing of dynamical exponents in low dimensional random media

A particle in a random potential with logarithmic correlations in dimensions $d=1,2$ is shown to undergo a dynamical transition at $T_{dyn}>0$. In $d=1$ exact results demonstrate that $T_{dyn}=T_c$, the static glass transition temperature, and that the dynamical exponent changes from $z(T)=2 + 2 (T_c/T)^2$ at high temperature to $z(T)= 4 T_c/T$ in the glass phase. The same formulae are argued to hold in $d=2$. Dynamical freezing is also predicted in the 2D random gauge XY model and related systems. In $d=1$ a mapping between dynamics and statics is unveiled and freezing involves barriers as well as valleys. Anomalous scaling occurs in the creep dynamics.Comment: 5 pages, 2 figures, RevTe

Dissociation of ssDNA - Single-Walled Carbon Nanotube Hybrids by Watson-Crick Base Pairing

The unwrapping event of ssDNA from the SWNT during the Watson-Crick base paring is investigated through electrical and optical methods, and binding energy calculations. While the ssDNA-metallic SWNT hybrid shows the p-type semiconducting property, the hybridization product recovered metallic properties. The gel electrophoresis directly verifies the result of wrapping and unwrapping events which was also reflected to the Raman shifts. Our molecular dynamics simulations and binding energy calculations provide atomistic description for the pathway to this phenomenon. This nano-physical phenomenon will open up a new approach for nano-bio sensing of specific sequences with the advantages of efficient particle-based recognition, no labeling, and direct electrical detection which can be easily realized into a microfluidic chip format.Comment: 4 pages, 4 figure