RESEARCH AREA – SENSORICS AND SPECTROMETRY
Research area: Sensorics
Major research activities in sensorics concern the development of high-Tc Josephson junctions and superconducting quantum interferometer devices (dc-SQUIDs) based on epitaxial YBaCuO films. The Josephson junctions are mainly of bicrystal type and used for Hilbert spectroscopy (single junction sensors) as well as for dc-SQUIDs (two junction sensors like one displayed in the picture on the right). The development of dc-SQUIDs includes also development of epitaxial superconducting multilayer flux transformers based on YBaCuO, PrBaCuO, SrTiO, and BaZrO perovskite films.
IFF-8 designed and fabricated dc-SQUIDs are used as very sensitive magnetic field sensors. In combination with a superconducting multilayer flux transformer IFF-8 has achieved a record magnetic field resolution of about 4 fT/sqrt(Hz) at 77 K. By construction of an electronic gradiometer comprising two such magnetometers a gradient resolution of about 1 fT/cm sqrt(Hz) at 77 K was achieved. IFF-8s high-Tc dc-SQUID sensors are available for internal and external customers since 1995 and used for, e.g., biomagnetic and geomagnetic sensing or for non-destructive evaluation as well as in elementary particles and material science.
The highest quality of epitaxial growth of the multilayer perovskite heterostructures is vital for the low noise performance of the sensors. This is strongly connected with further development of the deposition technology (sputtering machines) and microscopic methods (HRTEM) at IFF-8.
Research area: Spectrometry
IFF-8 in collaboration with Kotel'nikov Institute of Radio Engineering & Electronics of RAS develops Josephson detectors and spectroscopic applications of the ac Josephson effect to fill a spectral gap between the microwave and infrared ranges. Two types of spectroscopies are under study, namely, admittance spectroscopy and Hilbert spectroscopy, which are based on a modification of the dc I-V curve of a Josephson junction by external environment and external radiation, correspondingly. These spectroscopies might possess a unique combination of broad spectral span, high dynamic power range and fast electrically-driven scanning.
Development of special types of junctions, which should demonstrate Josephson oscillations with the narrowest linewidth and the broadest voltage-controlled frequency span, is a great challenge in this field. Due to the high energy gap of high-Tc superconductors, these materials have been chosen for junction development and, due to their small coherence lengths, only high-Tc grain-boundaries are considered for development of high-quality artificial junctions. An improvement of cation ordering and oxygen content at the grain-boundary region plus its impact on nonlinear static and dynamic characteristics of the high-Tc Josephson junctions are among the main goals of our research.
Spectral losses in the junction environment, associated with oxygen mobility in the grain boundary, optical phonon modes in high-Tc superconducting electrodes, substrate resonant modes, antennas, integrated with the junction, etc., are studied by admittance spectroscopy. Further development of the admittance spectroscopy to the stage, when it might be applied to any external sample in the junction environment, is one of the great challenges.
Spectra of various cw and pulsed radiation sources in the frequency range from a few GHz to a few THz are studied by Hilbert spectroscopy. Using radiation sources with continuous and polychromatic spectra, Hilbert spectroscopy might be applied for spectroscopic study of solid-state, liquid and gas samples in the applications, where high dynamic power range and high-speed measurements are required. A promising application of Hilbert spectroscopy to identification of bottled liquids in security systems, where speed and reliability of the measurements are of great importance, is under study.