Start of funding 01.01.2010

Spin and lattice degrees of freedom in Fe-based superconductors

Prof. Dr. Peter Böni
Technische Universität München
Physik-Department E21 - Experimental physics

Prof. Dr. M. Brian Maple
University of California, San Diego
Department of Physics Maple Group



Already now, superconductors are playing an increasingly important role in special applications such as in medicine, as high-Q electronic filters in base stations for mobile phones, as current limiting devices, and in science. To make superconductors applicable in a wider range of applications, however, it is necessary to identify and synthesize superconducting materials that can easily be processed. Recently, superconducting compounds LnFePO were identified (Ln is a lanthanide) that were found to be notably malleable in contrast to the high temperature superconductors. This is a key property to produce easy to work with superconducting electrical circuits. In a collaboration between the Californian team that is expert in growing LnFePO and the German team that has an extensive know-how in a large variety of neutron scattering, it is planned to investigate the influence of sample strain on the transition temperature and to identify the origin of the pairing interactions leading to superconductivity in LnFePO.

Final report:
Neutron scattering is an ideal tool to investigate spin and lattice degrees of freedoms in condensed matter, which are believed to be at the origin of the high-temperature superconductivity in a new class of iron pnictide high-Tc superconductors discovered in 2008, namely the family of LnFePO, where Ln is a lanthanide. In this collaboration between UCSD and TUM on this new type of unconventional superconductors we have discovered a new iron-pnictide family Ln2Fe12P7 that does not exhibit superconductivity but shows novel metallic behavior that seems to emerge due to competition between strong electronic correlations and magnetic frustration, and which may be of interest for novel electronic applications. The BaCaTeC travel funds allowed UCSD postdoc Marc Janoschek to perform neutron scattering experiments on such compounds at the FRM II neutron source at Garching using the facilities of the Munich group. Finally, a new project to further investigate these exciting new compounds in the San Diego group was already funded by the National Science Foundation, and will certainly further the collaboration between both groups.