112 research outputs found
Paired cut-wire arrays for enhanced transmission of transverse-electric fields through sub-wavelength slits in a thin metallic screen
It has recently been shown that the transmission of electromagnetic fields
through sub-wavelength slits (parallel to the electric field direction) in a
thin metallic screen can be greatly enhanced by covering one side of the screen
with a metallic cut-wire array laid on a dielectric layer. In this Letter, we
show that a richer phenomenology (which involves both electric- and
magnetic-type resonances) can be attained by pairing a second cut-wire array at
the other side of the screen. Via a full-wave comprehensive parametric study,
we illustrate the underlying mechanisms and explore the additional degrees of
freedom endowed, as well as their possible implications in the engineering of
enhanced transmission phenomena.Comment: 4 pages, 8 figures; slight corrections in Figs. 1, 2, and
Bandgap properties of low index contrast aperiodically ordered photonic quasicrystals
We numerically analyze, using Finite Difference Time Domain simulations, the
bandgap properties of photonic quasicrystals with a low index contrast. We
compared 8-, 10- and 12-fold symmetry aperiodically ordered lattices with
different spatial tiling. Our results show that tiling design, more than
symmetry, determines the transmission properties of these structures.Comment: 8 pages, 4 figures. To be published in Microwave and Optical
Technologies Letter
Superlensing properties of one-dimensional dielectric photonic crystals
We present the experimental observation of the superlensing effect in a slab
of a one-dimensional photonic crystal made of tilted dielectric elements. We
show that this flat lens can achieve subwavelength resolution in different
frequency bands. We also demonstrate that the introduction of a proper
corrugation on the lens surface can dramatically improve both the transmission
and the resolution of the imaged signal.Comment: 9 pages, 9 figure
Universal electronic structure of polar oxide hetero-interfaces
The electronic properties of NdGaO3/SrTiO3, LaGaO3/SrTiO3, and LaAlO3/SrTiO3 interfaces, all showing an insulator-to-metal transition as a function of the overlayer-thickness, are addressed in a comparative study based on x-ray absorption, x-ray photoemission and resonant photoemission spectroscopy. The nature of the charge carriers, their concentration and spatial distribution as well as the interface band alignments and the overall interface band diagrams are studied and quantitatively evaluated. The behavior of the three analyzed heterostructures is found to be remarkably similar. The valence band edge of all the three overlayers aligns to that of bulk SrTiO3. The near-interface SrTiO3 layer is affected, at increasing overlayer thickness, by the building-up of a confining potential. This potential bends both the valence and the conduction band downwards. The latter one crossing the Fermi energy in the proximity of the interface and determines the formation of an interfacial band offset growing as a function of thickness. Quite remarkably, but in agreement with previous reports for LaAlO3/SrTiO3, no electric field is detected inside any of the polar overlayers. The essential phenomenology emerging from our findings is discussed on the base of different alternative scenarios regarding the origin of interface carriers and their interaction with an intense photon beam
Experimental evidence of cut-wire-induced enhanced transmission of transverse-electric fields through sub-wavelength slits in a thin metallic screen
Recent numerical studies have demonstrated the possibility of achieving
substantial enhancements in the transmission of transverse-electric-polarized
electromagnetic fields through subwavelength slits in a thin metallic screen by
placing single or paired metallic cut-wire arrays at a close distance from the
screen. In this Letter, we report on the first experimental evidence of such
extraordinary transmission phenomena, via microwave (X/Ku-band) measurements on
printed-circuit-board prototypes. Experimental results agree very well with
full-wave numerical predictions, and indicate an intrinsic robustness of the
enhanced transmission phenomena with respect to fabrication tolerances and
experimental imperfections.Comment: 6 pages, 4 figures (slight revision
Persistent photoconductivity in 2-dimensional electron gases at different oxide interfaces
We report on the transport characterization in dark and under light
irradiation of three different interfaces: LaAlO3/SrTiO3, LaGaO3/SrTiO3, and
the novel NdGaO3/SrTiO3 heterostructure. All of them share a perovskite
structure, an insulating nature of the single building blocks, a polar/non-
polar character and a critical thickness of four unit cells for the onset of
conductivity. The interface structure and charge confinement in NdGaO3/SrTiO3
are probed by atomic-scale- resolved electron energy loss spectroscopy showing
that, similarly to LaAlO3/SrTiO3, extra electronic charge confined in a sheet
of about 1.5 nm in thickness is present at the NdGaO3/SrTiO3 interface.
Electric transport measurements performed in dark and under radiation show
remarkable similarities and provide evidence that the persistent perturbation
induced by light is an intrinsic peculiar property of the three investigated
oxide-based polar/non-polar interfaces. Our work sets a framework for
understanding the previous contrasting results found in literature about
photoconductivity in LaAlO3/SrTiO3 and highlights the connection between the
origin of persistent photoconductivity and the origin of conductivity itself.
An improved understanding of the photo- induced metastable electron-hole pairs
might allow to shed a direct light on the complex physics of this system and on
the recently proposed perspectives of oxide interfaces for solar energy
conversion.Comment: 11 pages, 7 figure
Multiple-magnon excitations shape the spin spectrum of cuprate parent compounds
Thanks to high resolution and polarization analysis, resonant inelastic x-ray
scattering (RIXS) magnetic spectra of La2CuO4, Sr2CuO2Cl2 and CaCuO2 reveal a
rich set of properties of the spin 1/2 antiferromagnetic square lattice of
cuprates. The leading single-magnon peak energy dispersion is in excellent
agreement with the corresponding inelastic neutron scattering measurements.
However, the RIXS data unveil an asymmetric lineshape possibly due to odd
higher order terms. Moreover, a sharp bimagnon feature emerges from the
continuum at (1/2,0), coincident in energy with the bimagnon peak detected in
optical spectroscopy. These findings show that the inherently complex spin
spectra of cuprates, an exquisite manifestation of quantum magnetism, can be
effectively explored by exploiting the richness of RIXS cross sections.Comment: 7 pages, 3 figure
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