Please select the desired project time frame:

• July 2026
• January 2026
• July 2025
• January 2025
• July 2024
• January 2024
• July 2023
• January 2023
• July 2022
• January 2022
• July 2021
• January 2021
• July 2020
• January 2020
• July 2019
• January 2019
• July 2018
• January 2018
• July 2017
• January 2017
• July 2016
• January 2016
• July 2015
• January 2015
• July 2014
• January 2014
• July 2013
• January 2013
• July 2012
• January 2012
• July 2011
• January 2011
• July 2010
• January 2010
• July 2009
• January 2009
• July 2008
• January 2008
• July 2007
• January 2007
• July 2006
• January 2006
• July 2005
• January 2005
• July 2004
• January 2004
• July 2003
• January 2003
• July 2002
• January 2002
• July 2001
• January 2001

Start of funding 01.07.2010

Multiorbital modeling of the magnetic and superconducting state in iron-based superconductors

---

The discovery of superconductivity in iron pnictides in 2008, which exhibit to date the highest critical temperature besides the copper based superconductors, has triggered enormous worldwide research activities with the aim to characterize and understand superconductivity in these novel compounds. In analogy to the copper based superconductors the superconductivity in the Fe pnictides emerges in the vicinity of an antiferromagnetic state and magnetic fluctuations appear as a natural origin for superconductivity in these materials. Multiple, strongly hybridized energy bands are a necessary ingredient for the theoretical modeling as a basis for the multitude of already available experimental results. The goal of this project .is to develop a microscopic description of the magnetic and the superconducting ground states of the iron pnictides based on a multiorbital model for their electronic structure. In the symmetry-broken magnetic state the Raman light scattering intensity, the dynamic spin susceptibility, and the optical conductivity will be calculated with an emphasis on the doping and the pressure dependence of the electronic structure and the intra- and interorbital interaction parameters. The thereby determined electronic band structure and the interaction parameters will serve as an input for the theoretical analysis of the superconducting and the magnetic properties.

Final report:
The complexity of the electronic physics in iron pnictides becomes evident from the observation that different symmetries of the superconducting state are realized in the various material classes of pnictides. In a selected compound this symmetry may even vary upon doping. In the collaboration of Dr. Graser and Professor Scalapino the basic experimentally accessible quantities for inelastic neutron and x- ray scattering were analyzed theoretically. The spectral weight of phonons with wavevectors which connect different sheets of the Fermi surface was thereby identified as a well suited signature to identify the symmetry of the superconducting state in different pnictides. The thereby developed calculational tools for analyzing the elctronic structure of pnictide materials were also timely applied to iron-selenide superconductors which were discovered in early 2010. Specifically the structure of the pairing interaction was examined and led to the prediction that spin-fluctuation mediated superconductivity in iron selenides should have d-wave pairing symmetry.

Explicit experimental tests were suggested to verify this prediction by inelastic neutron scattering. The results of the fruitful collaboration between the University of Augsburg and the UC Santa Barbara were published as two Rapid Communications in the journal Physical Review B.