High Q dielectric resonators using YBa2Cu3Ox thick films and polycrystalline dielectrics

Published versio

Ultralow loss polycrystalline alumina

Published versio

On stoichiometry and intermixing at the spinel/perovskite interface in CoFe2O4/BaTiO3 thin films

The performance of complex oxide heterostructures depends primarily on the interfacial coupling of the two component structures. This interface character inherently varies with the synthesis method and conditions used since even small composition variations can alter the electronic, ferroelectric, or magnetic functional properties of the system. The focus of this article is placed on the interface character of a pulsed laser deposited CoFe2O4/BaTiO3 thin film. Using a range of state-of-the-art transmission electron microscopy methodologies, the roles of substrate morphology, interface stoichiometry, and cation intermixing are determined on the atomic level. The results reveal a surprisingly uneven BaTiO3 substrate surface formed after the film deposition and Fe atom incorporation in the top few monolayers inside the unit cell of the BaTiO3 crystal. Towards the CoFe2O4 side, a disordered region extending several nanometers from the interface was revealed and both Ba and Ti from the substrate were found to diffuse into the spinel layer. The analysis also shows that within this somehow incompatible composite interface, a different phase is formed corresponding to the compound Ba2Fe3Ti5O15, which belongs to the ilmenite crystal structure of FeTiO3 type. The results suggest a chemical activity between these two oxides, which could lead to the synthesis of complex engineered interfaces

Perspective on room-temperature solid-state masers

The first solid-state masers to operate at room-temperature and ambient air-pressure were recently demonstrated using optically pumped spin-triplet states as the gain medium. In this Perspective, we briefly review the previous state-of-the-art in cryogenic solid-state masers and then discuss the development of the room-temperature solid-state maser: from the organic pentacene pulsed maser to the diamond nitrogen-vacancy continuous-wave maser. We characterize the operation of these masers as coherent microwave sources and ultra-low noise amplifiers before outlining how they can be adapted to act as model systems in which to explore room-temperature cavity quantum electrodynamics. After discussing challenges facing current embodiments of the room-temperature solid-state maser, we explore how they might be addressed or by-passed altogether through the development of alternative materials and masing mechanisms. Finally, we speculate on how the advent of masers that can operate in ambient conditions might lead to novel applications in metrology and quantum technologies

Enhanced magnetic Purcell effect in room-temperature masers

Recently, the world’s first room-temperature maser was demonstrated. The maser consisted of a sapphire ring housing a crystal of pentacene-doped p-terphenyl, pumped by a pulsed rhodamine-dye laser. Stimulated emission of microwaves was aided by the high quality factor and small magnetic mode volume of the maser cavity yet the peak optical pumping power was 1.4 kW. Here we report dramatic miniaturization and 2 orders of magnitude reduction in optical pumping power for a room-temperature maser by coupling a strontium titanate resonator with the spin-polarized population inversion provided by triplet states in an optically excited pentacene-doped p-terphenyl crystal. We observe maser emission in a thimble-sized resonator using a xenon flash lamp as an optical pump source with peak optical power of 70 W. This is a significant step towards the goal of continuous maser operation

Microwave dielectric loss in oxides: Theory and experiment

Published versio

SUPERCONDUCTING CURRENT LEADS OF YBCO AND PB-BSCCO

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Obtaining strong ferromagnetism in diluted Gd-doped ZnO thin films through controlled Gd-defect complexes

We demonstrate the fabrication of reproducible long-range ferromagnetism (FM) in highly crystalline Gdx Zn 1−xO thin films by controlling the defects. Films are grown on lattice-matched substrates by pulsed laser deposition at low oxygen pressures (≤25 mTorr) and low Gd concentrations (x ≤ 0.009). These films feature strong FM (10 μB per Gd atom) at room temperature. While films deposited at higher oxygen pressure do not exhibit FM, FM is recovered by post-annealing these films under vacuum. These findings reveal the contribution of oxygen deficiency defects to the long-range FM. We demonstrate the possible FM mechanisms, which are confirmed by density functional theory study, and show that Gd dopants are essential for establishing FM that is induced by intrinsic defects in these films