Ferroelectric domain walls are interfaces between areas of a material that exhibits different directions of spontaneous polarization. The properties of domain walls can be very different from those of the undisturbed material. Metallic-like conductivity of charged domain walls (CDWs) in nominally insulating ferroelectrics was predicted in 1973 and detected recently. This important effect is still in its infancy: The electric currents are still smaller than expected, the access to the conductivity at CDWs is hampered by contact barriers, and stability is low because of sophisticated domain structures or proximity of the Curie point. Here, we report on large, accessible, and stable conductivity at CDWs in lithium niobate (LN) crystals – a vital material for photonics. Our results mark a breakthrough: Increase of conductivity at CDWs by more than 13 orders of magnitude compared to that of the bulk, access to the effect via ohmic and diode-like contacts, and high stability for temperatures T ≤ 70 °C are demonstrated. A promising and now realistic prospect is to combine CDW functionalities with linear and nonlinear optical phenomena. Our findings allow new generations of adaptive-optical elements, of electrically controlled integrated-optical chips for quantum photonics, and of advanced LN-semiconductor hybrid optoelectronic devices.
Chip-integrated whispering-gallery resonators enable compact and wavelength-agile nonlinear optical frequency synthesizers. So far, the most flexible phase-matching technique, i.e. quasi phase matching, has not been applied in this configuration. The reason is the lack of suitable thin films with alternating crystal structure on a low-refractive-index substrate. Here, we demonstrate an innovative method of realizing thin film substrates suitable for quasi phase matching by field-assisted domain engineering of lithium niobate, and subsequent direct bonding and polishing. We are able to fabricate high-Q on-chip WGRs with these substrates by using standard semiconductor manufacturing techniques. The Q-factors of the resonators are up to one million, which allows us to demonstrate quasi-phase-matched second-harmonic generation in on-chip WGRs for the first time. The normalized conversion efficiency is 9 × 10 −4 mW −1 . This method can also be transferred to other material systems. * These authors contributed equally to this work.
Nonlinear interferometers allow for mid-infrared spectroscopy with near-infrared detection using correlated photons. Previous implementations have demonstrated a spectral resolution limited by spectrally selective detection. In our work, we demonstrate mid-infrared transmission spectroscopy in a nonlinear interferometer using single-pixel near-infrared detection and Fourier-transform analysis. A sub-wavenumber spectral resolution allows for rotational-lineresolving spectroscopy of gaseous samples in a spectral bandwidth of over 700 cm −1 . We use methane transmission spectra around 3.3 µm wavelength to characterize the spectral resolution, noise limitations and transmission accuracy of our device. The combination of nonlinear interferometry and Fourier-transform analysis paves the way towards performant and efficient mid-infrared spectroscopy with near-infrared detection.
Abstract:A new approach to the deposition of Mn12 single-molecule magnet monolayers on the functionalized Au(111) surface optimized for the investigation by means of scanning tunneling spectroscopy was developed. To demonstrate this method, the new Mn 12 complex [Mn12O12(O2CC6H4F)16(EtOH)4]‚ 4.4CHCl3 was synthesized and characterized. In MALDI-TOF mass spectra the isotopic distribution of the molecular ion peak of the latter complex was revealed. The complex was grafted to Au(111) surfaces via two different short conducting linker molecules. The Mn 12 molecules deposited on the functionalized surface were characterized by means of scanning tunneling microscopy showing homogeneous monolayers of highest quality. Scanning tunneling spectroscopy measurements over a wider energy range compared with previous results could be performed because of the optimized Au(111) surface functionalization. Furthermore, the results substantiate the general suitability of short acidic linker molecules for the preparation of Mn 12 monolayers via ligand exchange and represent a crucial step toward addressing the magnetic properties of individual Mn12 single-molecule magnets.
Despite the need for isotropic optical resolution in a growing number of applications, the majority of super-resolution fluorescence microscopy setups still do not attain an axial resolution comparable to that in the lateral dimensions. Three-dimensional (3D) nanoscopy implementations that employ only a single objective lens typically feature a trade-off between axial and lateral resolution. 4Pi arrangements, in which the sample is illuminated coherently through two opposing lenses, have proven their potential for rendering the resolution isotropic. However, instrument complexity due to a large number of alignment parameters has so far thwarted the dissemination of this approach. Here, we present a 4Pi-STED setup combination, also called isoSTED nanoscope, where the STED and excitation beams are intrinsically co-aligned. A highly robust and convenient 4Pi cavity allows easy handling without the need for readjustments during imaging experiments.
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