RESUMEN
We demonstrate a new nanoscale spectroscopic technique that combines subwavelength near-field imaging with broadband interference spectroscopy. We apply this technique to study phase spectra of surface plasmons in individual gold nanoparticles and nanoparticle dimers. Collective plasmon oscillations in selected nanostructures are excited by a femtosecond white-light continuum transmitted through a subwavelength aperture. The interference spectra detected in the far field result from the coherent superposition of the aperture field and the secondary field re-emitted by the nanostructure. The analysis of these spectra allows us to accurately measure the positions and damping constants of single-nanostructure plasmon resonances.
RESUMEN
The magnetization, M(H< or =30 T,0.7< or =T< or =300 K), of (C5H12N)2CuBr4 has been used to identify this system as an S = 1/2 Heisenberg two-leg ladder in the strong-coupling limit, J( perpendicular) = 13.3 K and J( parallel) = 3.8 K, with H(c1) = 6.6 T and H(c2) = 14.6 T. An inflection point in M(H,T = 0.7 K) at half saturation, M(s)/2, is described by an effective XXZ chain. The data exhibit universal scaling behavior in the vicinity of H(c1) and H(c2), indicating that the system is near a quantum critical point.