Traditional photonic structures such as photonic crystals utilize a) large arrays of small features with the same size and pitch and b) a small number of larger features such as diffraction outcouplers. In conventional nanofabrication, separate lithography and etch steps are used for small and large features in order to employ process parameters that lead to optimal pattern transfer and side-wall profiles for each feature-size category, thereby overcoming challenges associated with RIE lag. This approach cannot be scaled to more complex photonic structures such as those emerging from inverse design protocols. Those structures include features with a large range of sizes such that no distinction between small and large can be made. We develop a sleeve and bulk etch protocol that can be employed to simultaneously pattern features over a wide range of sizes while preserving the desired pattern transfer fidelity and sidewall profiles. This approach reduces the time required to develop a robust process flow, simplifies the fabrication of devices with wider ranges of feature sizes, and enables the fabrication of devices with increasingly complex structure.

As a prototypical Mott insulator with ferromagnetic ordering, YTiO3 (YTO) is of great interest in the study of strong electron correlation effects and orbital ordering. Here we report the first molecular beam epitaxy (MBE) growth of YTO films, combined with theoretical and experimental characterization of the electronic structure and charge transport properties. The obstacles of YTO MBE growth are discussed and potential routes to overcome them are proposed.DC transport and Seebeck measurements on thin films and bulk single crystals identify p-type Arrhenius transport behavior, with an activation energy of ~ 0.17 eV in thin films, consistent with the energy barrier for small hole polaron migration from hybrid density functional theory (DFT) calculations. Hard X-ray photoelectron spectroscopy measurements (HAXPES) show the lower Hubbard band (LHB) at 1.1 eV below the Fermi level, whereas a Mott-Hubbard band gap of ~1.5 eV is determined from photoluminescence (PL) measurements. These findings provide critical insight into the electronic band structure of YTO and related materials.

We present a combined Brillouin light scattering (BLS) and micromagnetic simulation investigation of the magnetic-field-dependent spin-wave spectra in a hybrid structure made of permalloy (NiFe) artificial spin-ice (ASI) systems, composed of stadium-shaped nanoislands, deposited on the top of an unpatterned permalloy film with a nonmagnetic spacer layer. The thermal spin-wave spectra were recorded by BLS as a function of the magnetic field applied along the symmetry direction of the ASI sample. Magneto-optic Kerr effect magnetometry was used to measure the hysteresis loops in the same orientation as the BLS measurements. The frequency and the intensity of several spin-wave modes detected by BLS were measured as a function of the applied magnetic field. Micromagnetic simulations enabled us to identify the modes in terms of their frequency and spatial symmetry and to extract information about the existence and strength of the dynamic coupling, relevant only to a few modes of a given hybrid system. Using this approach, we suggest a way to understand if the dynamic coupling between ASI and film modes is present or not, with interesting implications for the development of future three-dimensional magnonic applications and devices.

Disorder is an essential parameter in photonic systems and devices, influencing phenomena such as the robustness of topological photonic states and the Anderson localization of modes in waveguides. We develop and demonstrate a method for both analyzing and visualizing positional, size, and shape disorder in periodic structures such as photonic crystals. This analysis method shows selectivity for disorder type and sensitivity to disorder down to less than 1%. We show that the method can be applied to more complex shapes such as those used in topological photonics. The method provides a powerful tool for process development and quality control, including analyzing the precision of E-Beam Lithography before patterns are transferred; quantifying the precision limits of lithography, deposition, or etch processes; and studying the intentional displacement of individual objects within otherwise periodic arrays.

We report advancements in material growth, device design, and device fabrication that facilitate development of a scalable platform for quantum photonics using site-templated wavelength-tunable InAs quantum dot molecules to overcome spatial and spectral inhomogeneity.