Subsequent projects

Nematic order and new phases in quantum materials

We plan to study basic physical principles at the heart of new phases in solids such as structural transformations, spin and charge order or superconductivity. Among the most exciting yet insufficiently explored driving instabilities, we identify nematic electronic order, which breaks the rotational but maintains the translational symmetry. It is supposed to be relevant in a broad class of materials including heavy Fermion systems, ruthenates, cuprates and Fe-based compounds. Raman scattering is among the few techniques which allow the direct detection of nematic order. Therefore we plan to study various ordering phenomena and the related precursors using light scattering from electrons and lattice vibrations. The response functions relating to either spin nematicity or charge (orbital) ordering will be constructed theoretically on a microscopic basis.

Primary project: Materials with coupled order parameters under extreme conditions

Final Report

The project “Nematic order and new phases in quantum materials” between Prof. Thomas P. Devereaux at Stanford University and Dr. Rudi Hackl at the Walther Meissner Institut (WMI) in Garching was supported by BaCaTeC from January 1, 2013 to December 31, 2014. In this period the iron-based superconductor Ba1-xKxFe2As2 and the related parent and electron-doped compounds were studied exhibiting nematic fluctuations at low doping. For Ba0.6K0.4Fe2As2 it could be shown that two competing channels contribute to Cooper pairing [T. Böhm et al., Phys. Rev. X 4, 041046 (2014)]. Presently, three more papers are in preparation including one on chiral excitations. The collaboration with the group of Prof. Ian Fisher at Stanford, that was established during the first funding period of BaCaTeC (21 [2007-2]), resulted in a joint publication on the tritellurides [H.-M. Eiter et al., PNAS 110, 64 (2013)]. Among the scientists supported by BaCaTeC there were 5 young researchers: Dr. Elizabeth A. Nowadnick (Stanford University, now Cornell, visit in Garching in the period February 6-21, 2013), Associate Staff Scientist Dr. Brian Moritz (SLAC, National Accelerator Laboratory, July 23-27, 2013 and June 19-27, 2014), Dipl. Phys. Thomas Böhm (WMI, visit in Stanford December 2012-June 2013, September 18 – October 7, 2014 and November 21 – December 16, 2014), Dipl. Phys. Florian Kretzschmar (WMI, visit in Stanford March 23 – 29, 2013), and Dipl. Phys. Andreas Baum (WMI, visit in Stanford September 18 – October 7, 2014). E. A. Nowadnick, B. Moritz, F. Kretzschmar and T. Böhm delivered seminar talks in Garching and Stanford. The Bavarian partner submitted two proposals to the DFG on subjects partially or directly related to the research funded by BaCaTeC.


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