The detection of small changes in the wavelength position of localized surface plasmon resonances in metal nanostructures has been used successfully in applications such as label-free detection of ...biomarkers. Practical implementations, however, often suffer from the large spectral width of the plasmon resonances induced by large radiative damping in the metal nanocavities. By means of a tailored design and using a reproducible nanofabrication process, high quality planar gold plasmonic nanocavities are fabricated with strongly reduced radiative damping. Moreover, additional substrate etching results in a large enhancement of the sensing volume and a subsequent increase of the sensitivity. Coherent coupling of bright and dark plasmon modes in a nanocross and nanobar is used to generate high quality factor subradiant Fano resonances. Experimental sensitivities for these modes exceeding 1000 nm/RIU with a Figure of Merit reaching 5 are demonstrated in microfluidic ensemble spectroscopy.
Subradiant and superradiant plasmon modes in concentric ring/disk nanocavities are experimentally observed. The subradiance is obtained through an overall reduction of the total dipole moment of the ...hybridized mode due to antisymmetric coupling of the dipole moments of the parent plasmons. Multiple Fano resonances appear within the superradiant continuum when structural symmetry is broken via a nanometric displacement of the disk, due to coupling with higher order ring modes. Both subradiant modes and Fano resonances exhibit substantial reductions in line width compared to the parent plasmon resonances, opening up possibilities in optical and near IR sensing via plasmon line shape design.
Nanostructured superconductors Moshchalkov, Victor V; Moshchalkov, Victor V; Fritzsche, Joachim
2011., 2011, 2011-03-28
eBook
The main focus of the book is to present the effects of nanostructuring on superconducting critical parameters. Optimizing systematically flux and condensate confinement in various nanostructured ...superconductors, ranging from single nano-cells to their huge arrays, critical fields and currents can be increased up to their theoretical limits, thus drastically improving the potential for practical applications of nanostructured superconductors.
Unidirectional side scattering of light by a single-element plasmonic nanoantenna is demonstrated using full-field simulations and back focal plane measurements. We show that the phase and amplitude ...matching that occurs at the Fano interference between two localized surface plasmon modes in a V-shaped nanoparticle lies at the origin of this effect. A detailed analysis of the V-antenna modeled as a system of two coherent point-dipole sources elucidates the mechanisms that give rise to a tunable experimental directivity as large as 15 dB. The understanding of Fano-based directional scattering opens a way to develop new directional optical antennas for subwavelength color routing and self-referenced directional sensing. In addition, the directionality of these nanoantennas can increase the detection efficiency of fluorescence and surface enhanced Raman scattering.
We observe the appearance of Fano resonances in the optical response of plasmonic nanocavities due to the coherent coupling between their superradiant and subradiant plasmon modes. Two ...reduced-symmetry nanostructures probed via confocal spectroscopy, a dolmen-style slab arrangement and a ring/disk dimer, clearly exhibit the strong polarization and geometry dependence expected for this behavior at the individual nanostructure level, confirmed by full-field electrodynamic analysis of each structure. In each case, multiple Fano resonances occur as structure size is increased.
Crystalline and amorphous structures are two of the most common solid‐state phases. Crystals having orientational and periodic translation symmetries are usually both short‐range and long‐range ...ordered, while amorphous materials have no long‐range order. Short‐range ordered but long‐range disordered materials are generally categorized into amorphous phases. In contrast to the extensively studied crystalline and amorphous phases, the combination of short‐range disordered and long‐range ordered structures at the atomic level is extremely rare and so far has only been reported for solvated fullerenes under compression. Here, a report on the creation and investigation of a superconducting quasi‐1D material with long‐range ordered amorphous building blocks is presented. Using a diamond anvil cell, monocrystalline (TaSe4)2I is compressed and a system is created where the TaSe4 atomic chains are in amorphous state without breaking the orientational and periodic translation symmetries of the chain lattice. Strikingly, along with the amorphization of the atomic chains, the insulating (TaSe4)2I becomes a superconductor. The data provide critical insight into a new phase of solid‐state materials. The findings demonstrate a first ever case where superconductivity is hosted by a lattice with periodic but amorphous constituent atomic chains.
Combination of long‐range ordered and short‐range disordered structures at the atomic level is demonstrated for a quasi‐1D linear chain compound. Under compression, the constituent atomic chains of the material are amorphized without breaking the orientational and periodic translation symmetries of the chain lattice. This lattice of amorphous atomic chains hosts a quantum condensate of Cooper pairs.
We present direct experimental mapping of the lateral magnetic near-field distribution in plasmonic nanoantennas using aperture scanning near-field optical microscopy (SNOM). By means of full-field ...simulations it is demonstrated how the coupling of the hollow-pyramid aperture probe to the nanoantenna induces an effective magnetic dipole which efficiently excites surface plasmon resonances only at lateral magnetic field maxima. This excitation in turn affects the detected light intensity enabling the visualization of the lateral magnetic near-field distribution of multiple odd and even order plasmon modes with subwavelength spatial resolution.
The emergence of superconductivity in doped insulators such as cuprates and pnictides coincides with their doping‐driven insulator–metal transitions. Above the critical doping threshold, a metallic ...state sets in at high temperatures, while superconductivity sets in at low temperatures. An unanswered question is whether the formation of Cooper pairsin a well‐established metal will inevitably transform the host material into a superconductor, as manifested by a resistance drop. Here, this question is addressed by investigating the electrical transport in nanoscale rings (full loops) and half loops manufactured from heavily boron‐doped diamond. It is shown that in contrast to the diamond half‐loops (DHLs) exhibiting a metal–superconductor transition, the diamond nanorings (DNRs) demonstrate a sharp resistance increase up to 430% and a giant negative “magnetoresistance” below the superconducting transition temperature of the starting material. The finding of the unconventional giant negative “magnetoresistance”, as distinct from existing categories of magnetoresistance, that is, the conventional giant magnetoresistance in magnetic multilayers, the colossal magnetoresistance in perovskites, and the geometric magnetoresistance in semiconductor–metal hybrids, reveals the transformation of the DNRs from metals to bosonic semiconductors upon the formation of Cooper pairs. DNRs like these could be used to manipulate Cooper pairs in superconducting quantum devices.
Nanoscale “diamond rings” provide unconventional giant “magnetoresistance” for the development of new quantum devices. The unconventional giant “magnetoresistance” caused by the trapping of Cooper pairs within the heavily boron‐doped diamond nanorings, distinguishes itself from the conventional giant magnetoresistance originating from spin‐dependent scattering of single electrons in layered magnetic materials.
Vortices play a crucial role in determining the properties of superconductors as well as their applications. Therefore, characterization and manipulation of vortices, especially at the single-vortex ...level, is of great importance. Among many techniques to study single vortices, scanning tunnelling microscopy (STM) stands out as a powerful tool, due to its ability to detect the local electronic states and high spatial resolution. However, local control of superconductivity as well as the manipulation of individual vortices with the STM tip is still lacking. Here we report a new function of the STM, namely to control the local pinning in a superconductor through the heating effect. Such effect allows us to quench the superconducting state at nanoscale, and leads to the growth of vortex clusters whose size can be controlled by the bias voltage. We also demonstrate the use of an STM tip to assemble single-quantum vortices into desired nanoscale configurations.
In nanoplasmonic sensing, the bulk refractive index sensitivity is often used as a metric for performance evaluation. However, for biosensing applications, which involve molecular binding events, ...only the refractive index in a confined region close to the metal surface is altered. The correlation between the bulk and the surface sensitivity strongly depends on the nanostructure geometry, especially in strongly coupled systems. In this paper, we thoroughly investigate the surface sensing performance of diffractively coupled plasmonic crystals using the atomic layer deposition of conformal Al2O3 layers with well-defined thickness and refractive index. It is demonstrated that the surface sensing capacity cannot be fully described by the bulk sensitivity. It not only shows opposite dependence on the coupling strength compared to the bulk sensitivity, but also the bulk sensitivity cannot reflect the fact that the surface sensitivity could be different in different thickness ranges on the metal surface. The reason rests on the different decay lengths of the plasmonic crystal arrays with different coupling strengths and can be well explained by the second order surface sensitivity that has recently been proposed. Furthermore, we provide a quantitative method to evaluate the surface sensing performance of specific target analyte. This method is generic and can be applied to other nanoplasmonic systems and a broad range of biomolecules with various sizes.
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