Hermann Group

Superconductivity was discovered in 1911, but the discovery by Dr. Hermann's group of a Tl-Ca-Ba-Cu-O superconductor with a critical-temperature of 125°K, on the heels of a 1987 Nobel-prize-winning discovery of high temperature superconductivity in the La-Ba-Ca-O system, helped spark a world-wide race to understand and develop oxide superconductors. Anticipated applications for bulk superconductors include no-loss transmission of electricity, inexpensive energy storage, and high-speed, magnetically levitated trains. In addition, superconductors may be used in thin film form for passive microwave applications.

Research by Dr. Hermann's group includes bulk synthesis and doping of new high critical temperature (Tc) superconducting compounds, single crystal growth of high Tc superconductors, thin film deposition of precursor films and subsequent vapor phase Tl reaction (including substrate studies), and superconductor thin film deposition by laser ablation.

Additionally, an array of measurement techniques have been established in the CU superconductor laboratory, including automated resistance and ac susceptibility measurements using a closed-cycle refrigerator, flux creep in superconducting single crystals by high field ac susceptibility measurements, thermoelectric power and Nernst effect measurements, Hall effect measurements, and powder pattern and single crystal X-ray diffraction in collaboration with the CU Geological Sciences Department. Access to the nearby NIST Superconducting Quantum Interface Device Magnetometers allows a complete range of magnetic measurements as well.

Studies are also underway on new types of frequency tuneable microwave devices based on HTSC films integrated with non-linear dielectric films for telecommunications applications. This work is carried out in collaboration with Physics Professors Price and Rogers, with Electrical and Computer Engineering colleagues, and is funded by federal and state governments as well as by a local industrial partner. The films are deposited by sputtering and by pulsed laser deposition.

Dr. Hermann also directs a non-superconductor research project to investigate the deposition and processing of photovoltaic structures based on thin-film CuInSe2. Recent world-record-breaking solar to electric conversion efficiencies of >16% have been achieved in a collaborative project with the National Renewable Energy Laboratory in Golden, Co. Current emphasis is on cost-effective large-area deposition techniques such as electrodeposition.

Selected Publications