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Los Alamos National LaboratoryCenter for Integrated Nanotechnologies
Helping you understand, create, and characterize nanomaterials
DOE

2014

Select science highlights from 2014.

Archived highlights

First Infrared Quantum Dots to Stop Blinking

quntum dots
October 3, 2013

Non-blinking excitonic emission from near-infrared (NIR) and type-II nanocrystal quantum dots (NQDs) is reported for the first time, coupled with suppressed Auger recombination (AR). To realize this unusual degree of stability at the single-dot level, novel InP/CdS core/shell NQDs were synthesized for a range of shell thicknesses (~1-11 monolayers of CdS).

quntum dots

Significance: This new system demonstrates that electronic structure and shell thickness can be employed together to effect control over key single-dot and ensemble NQD photophysical properties. Suppressed-blinking, NIR emitting NQDs are ideal candidates molecular probes for single-particle tracking; suppressed AR has important implications for optical amplification and lasing. quntum dots graph

Optimizing Electronic Correlations for Superconductivity

superconductivity
June 23, 2014

By incoporating the bad metal nature of the normal state, we have provided a unified understanding of superconducting pairing in diverse iron-based superconductors.

graph near a Mott transition

Above drawing shows a schematic phase diagram near a Mott transition. The parent compounds of alkaline iron selenides and iron pnictides are located on two sides of the Mott transition but exhibit similar strength of superconducting pairing upon carrier doping.

Significance: Our study reveals an important principle that superconductivity is optimized at the border between itinerancy and electronic localization. This principle should apply beyond the context of iron pnictides and chalcogenides, and is expected to guide the search for superconductors with even higher transition temperatres.

Research Details: We have applied a strong-coupling approach to reveal the comparable pairing strength in the alkaline iron selenides and iron pnictides. Our results uncover a univerality in the exitsing and emerging iron-based high-temperature superconductors with very diverse materials and Fermi-surface characteristics.

Strong coupling in the sub-wavelength limit using metamaterial nanocavities

quntum dots
June 25, 2014

Strong light-matter coupling between a metamaterial and an intersubband transition in semiconductor heterostructures is fully scalable from the mid-infrared (~10 mm) to the near-infrared (~1.5 mm) and happens on a single nanocavity level in deep sub-wavelength volumes.

graph near a Mott transition

(left) Schematic of a “dogbone” metamaterial nanocavity strongly coupled to optical dipoles (indicated by the vertical arrows). (right) Scanning electron micrograph image of a fabricated nanocavity with a resonance frequency of 22 THz.

Significance: Plasmonic metamaterials offer the possibility to control light in all three dimensions. Here, we experimentally demonstrate strong light-matter coupling between a single nanocavity and intersubband transitions in heterostructures. Such systems show great potential for the realization of electrically tunable optical filters and modulators at any given wavelength or for studying unusual effects such as superradiance.

Research Details:

  • The structure consists of metallic nanocavities fabricated using a combination of electron-beam lithography and metal evaporation. Typical feature sizes are approximately 100 nm for mid-infrared and 30 nm for near-infrared samples.
  • Transmission spectra were measured at CINT using a Fourier-transform infrared spectrometer. Numerical calculations were performed for a periodic array of “dogbone” nanocavities supporting strong field enhancement in their vicinity without the need of an additional ground plane.

Induced transparency by coupling of Tamm and defect states in tunable terahertz plasmonic crystals

tamm coupling
June 26, 2014

Observation of Tamm and Defect states in tunable THz plasmonic crystals. Resonant coupling between states on opposite edges of the crystal allowed observation of induced transparency across several crystal periods.

graph tamm states

Tamm states in plasmonic crystal-defect structures. (a) Schematic of the sample configured such that a four-period plasmonic crystal, tuned by G1, with adjacent plasmonic defect, tuned by G2, is formed between S and G3. (b) The plasmonic detection region is indicated in red. Plots of the plasmonic photovoltage spectra as a function of VG1 and VG2 are shown for 302.5 GHz excitation frequency. (c) The calculated bandgaps (grey) of the infinite plasmonic crystal and the plasmonic crystal–plasmonic defect system modes (blue) are plotted for 302.5 GHz.

Significance: The engineering of plasmonic resonators in situ rather than solely through lithographic tuning of the physical geometry opens a previously unexplored avenue for the study of strongly coupled electro-magnetic systems.

Research Details:

  • System studied is a high mobility two-dimensional electron gas device grown and fabricated at CINT.
  • Plasmonic crystals, which can be thought of as photonic crystals fabricated from plasmonic materials, Bragg scatter incident electromagnetic waves from a repeated unit cell. However, plasmonic crystals, like metamaterials, are composed of subwavelength unit cells.
  • Over 50% tuning of plasmonic crystal bandgaps demonstrated. Graphene and GaN may allow higher temperature (>77K) observation of these effects.
  • Plasmon-induced transparency phenomenon observed by electronic tuning of plasmonic modes with fixed excitation frequency.