Infrared evidence of a Slater metal-insulator transition in NaOsO3

The magnetically driven metal-insulator transition (MIT) was predicted by Slater in the fifties. Here a long-range antiferromagnetic (AF) order can open up a gap at the Brillouin electronic band boundary regardless of the Coulomb repulsion magnitude. However, while many low-dimensional organic conductors display evidence for an AF driven MIT, in three-dimensional (3D) systems the Slater MIT still remains elusive. We employ terahertz and infrared spectroscopy to investigate the MIT in the NaOsO3 3D antiferromagnet. From the optical conductivity analysis we find evidence for a continuous opening of the energy gap, whose temperature dependence can be well described in terms of a second order phase transition. The comparison between the experimental Drude spectral weight and the one calculated through Local Density Approximation (LDA) shows that electronic correlations play a limited role in the MIT. All the experimental evidence demonstrates that NaOsO3 is the first known 3D Slater insulator.Comment: 4 figure

Mid-Infrared Plasmonic Biosensing with Graphene

Infrared spectroscopy is the technique of choice for chemical identification of biomolecules through their vibrational fingerprints. However, infrared light interacts poorly with nanometric-size molecules. We exploit the unique electro-optical properties of graphene to demonstrate a high-sensitivity tunable plasmonic biosensor for chemically specific label-free detection of protein monolayers. The plasmon resonance of nanostructured graphene is dynamically tuned to selectively probe the protein at different frequencies and extract its complex refractive index. Additionally, the extreme spatial light confinement in graphene—up to two orders of magnitude higher than in metals—produces an unprecedentedly high overlap with nanometric biomolecules, enabling superior sensitivity in the detection of their refractive index and vibrational fingerprints. The combination of tunable spectral selectivity and enhanced sensitivity of graphene opens exciting prospects for biosensing.Peer ReviewedPostprint (author's final draft

Resolving molecule-specific information in dynamic lipid membrane processes with multi-resonant infrared metasurfaces

A multitude of biological processes are enabled by complex interactions between lipid membranes and proteins. To understand such dynamic processes, it is crucial to differentiate the constituent biomolecular species and track their individual time evolution without invasive labels. Here, we present a label-free mid-infrared biosensor capable of distinguishing multiple analytes in heterogeneous biological samples with high sensitivity. Our technology leverages a multi-resonant metasurface to simultaneously enhance the different vibrational fingerprints of multiple biomolecules. By providing up to 1000-fold near-field intensity enhancement over both amide and methylene bands, our sensor resolves the interactions of lipid membranes with different polypeptides in real time. Significantly, we demonstrate that our label-free chemically specific sensor can analyze peptide-induced neurotransmitter cargo release from synaptic vesicle mimics. Our sensor opens up exciting possibilities for gaining new insights into biological processes such as signaling or transport in basic research as well as provides a valuable toolkit for bioanalytical and pharmaceutical applications

Investigation of Terahertz and Mid-Infrared Metamaterials

In this work metamaterial devices for the terahertz (THz) and mid-infrared (Mid-IR) spectral range have been simulated, fabricated by electron beam lithography and experimentally investigated by Fourier Transform Infrared Spectroscopy. We could implement active devices for the THz range, based on high temperature superconductors, exhibiting a tunable resonant response driven by temperature. Moreover we designed and studied plasmonic devices for the mid-IR range with optimized electric field profile and performance for high sensitivity surface plasmon-based environmental sensors

Investigation of Terahertz and Mid-Infrared Metamaterials

In this work metamaterial devices for the terahertz (THz) and mid-infrared (Mid-IR) spectral range have been simulated, fabricated by electron beam lithography and experimentally investigated by Fourier Transform Infrared Spectroscopy. We could implement active devices for the THz range, based on high temperature superconductors, exhibiting a tunable resonant response driven by temperature. Moreover we designed and studied plasmonic devices for the mid-IR range with optimized electric field profile and performance for high sensitivity surface plasmon-based environmental sensors

Substrateless micrometric metal mesh for mid-infrared plasmonic Sensors

We fabricated large-area substrateless metal meshes with micrometric period. The measured mid-infrared (IR) spectra display resonant features with high Q-factor due to the interaction of the radiation with Surface Plasmon (SP) modes on both faces of the film. The devices can be used for SP-based sensors. © 2010 IEEE

Substrateless micrometric metal mesh for mid-infrared plasmonic sensors

We report on the fabrication and optical properties of thin metal films periodically patterned with square hole arrays of 2 micron pitch, which behave as substrateless plasmonic devices at mid-infrared frequencies. Large (3x3 mm(2)) meshes were fabricated by metallizing a patterned silicon nitride membrane. The mid-infrared spectra display resonant absorption lines with a Q-factor up to 22 in both transmission and reflection, due to the interaction of the radiation with surface plasmon modes on both faces of the film, allowed by substrate removal. The devices can be used to fabricate surface plasmon-based chemical sensors employing mid-infrared radiation

Midinfrared surface plasmon sensor based on a substrateless metal mesh

A midinfrared mass sensor based on high quality factor surface plasmon modes was designed, fabricated, and tested by infrared spectroscopy for the detection of nanometric layers of dielectric materials. Substrate removal below a metal mesh with period of 2 mu m results in the coupling between degenerate surface plasmon modes on the two surfaces, resulting in a quality factor up to 33 for the antisymmetric mode. The presented substrateless metal mesh integrates mass sensing capability together with midinfrared spectroscopy, and is therefore of potential interest for substance-selective environmental and biomedical sensing applications (C) 2011 American Institute of Physics. [doi:10.1063/1.3559616

Self-Similar Multiresonant Nanoantenna Arrays for Sensing from Near- to Mid-Infrared

Tailoring nanoscale light concentration and electromagnetic near-field enhancement over a broad spectral range is crucial for many photonics applications such as infrared spectroscopy, photodetection, and light harvesting. So far, broadband light enhancement has faced significant challenges due to the difficulty of efficiently exciting resonances at spectrally separated wavelengths and the inability of current devices to individually tune each specific resonance. Here, we introduce a multiresonant structure based on the non-overlapping combination of plasmonic nano antenna arrays with multiple periodicities. The self-similarity of the multiperiodic array, obtained by a fractal-like generation procedure, enables the excitation of a high number of resonances without compromising their excitation efficiency. We experimentally demonstrate devices with up to four independent resonances covering an unprecedentedly wide spectral range from 10 to 1.5 mu m. Significantly, the reflectance signal is uniformly strong for all the resonances, reaching more than 70% amplitude and near-field intensity enhancements above 1000. We further show that each individual resonance wavelength can be independently controlled over a 50% spectral range by modifying a single geometrical antenna parameter, providing superior flexibility in tailoring the overall spectral response. Due to the self-similar layout and independent resonances, our design is well described by temporal coupled-mode theory, allowing for a straightforward extension for other nanophotonic applications. Finally, we demonstrate that the wide spectral coverage of our design enables a unique sensing method by simultaneously performing chemically specific mid-infrared detection and near infrared refractometry