Mesoscopic approaches to probing low-energy electronic excitations in heavy fermion materials

QMI Seminars

Speaker: Oleksandr Foyevtsov, Goethe University, Frankfurt am Main
Date & Time: April 25, 2014 11:00 - 12:00
Location: UBC, AMPEL 311
Local Contact: George Sawatzky
Intended Audience: Graduate

Superconductivity (SC) in so-called heavy-fermion (HF) materials tends to be unconventional and intimately related to the electron degrees of freedom in a crystal environment. The family of CeMIn₅ compounds is a famous example of such HF materials. In addition to SC, which features some similarities with high-Tc cuprates, they may also demonstrate exotic order, such as the Fulde-Ferrel-Larkin-Ovchinnikov state observed in CeCoIn₅, be tuned to Quantum Critical Point, etc.

Planar tunneling spectroscopy is one of the most direct probes of the electronic excitations, particularly dealing with the low-E ones which are the source of the intriguing low-T physics in the HF compounds. At the same time, it requires thin films of high quality. Achieving suitable quality is a case-to-case issue, but so far thin films of only several HF compounds have been obtained with satisfactory results. In spite of our limited success in improving the quality of the CeCoIn₅ thin films, we found the films suitable for structuring on a mesoscopic scale. As a result, we successfully prepared and performed a series of electronic transport measurements on individually connected CeCoIn₅ thin film growth domains. The prepared mesostructures in planar tunneling geometries demonstrated strongly non-linear low-T characteristics. Utilizing the same preparation process we also prepared micron-sized SQUID interferometers on CeCoIn₅ thin film growth domains. The characterization of these interferometers showed both a well understood behavior as well as some unexpected features, which will be discussed in the talk. The richness of the HF physics, in particular that of CeCoIn₅, the power of the interferometry and time-of-flight like experiments, as well as the capabilities of modern microstructuring techniques clearly motivate for future experiments, which also may be extended to other materials with correlated electronic properties.