Investigation of the electronic properties of iron-based superconductors with focus on the interaction of superconducting and magnetic order parameters in the coexistence phase

• Applicant: Dr. Philipp Materne
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 328852140

• Final Report Year: 2019

Final Report Abstract

In summary I and my collaborators investigated the local magnetic order parameter in LaFeAsO, CeFeAsO, and BaFe2 S3 as a function of hydrostatic pressure. We found that LaFeAsO and CeFeAsO behave completely opposite and that chemical pressure in CeFeAs1−x Px is comparable with hydrostatic pressure in LaFeAsO. We provided the first local magnetic phase diagram as well as the first pressure study of the crystallographic parameters in CeFeAsO. Future research should focus on the determination of the local magnetic order parameter using SMS of the other 1111 compounds, namely Pr-/Nd-/SmFeAsO. By combining this local probe studies with the pressure dependence of the crystallographic parameters a complete set of data can be generated which will provide additional inside in the interaction of electronic and structural degrees of freedom. In BaFe2 S3 we provided the first local magnetic phase diagram over the full pressure range. As a result of this study, the pressure dependence of the magnetic order in BaFe2 S3 can be qualitatively explained by a combination of a bandwidth-controlled insulator-metal transition, a pressure enhanced exchange interaction between Fe-atoms, and Fe 3d-S 3p hybridization. Future work can study the influence of chemical substitution, e.g. Ba → Sr, in combination with external pressure on the magnetic order parameter. Eventually my project has shown the power and uniqueness of SMS to determine the local magnetic order parameter under pressure. In addition I have shown the incredible resolution of the hybrid operation mode of the Advanced Photon Source.

Publications

• Microscopic phase diagram of LaFeAsO single crystals under pressure, Phys. Rev. B 98, 174510 (2018)
  Materne, P. and Bi, W. and Zhao, J. and Hu, M. Y. and Kappenberger, R. and Wurmehl, S. and Aswartham, S. and Büchner, B. and Ercan Alp, E.
  
• Superconducting and magnetic phase diagram of RbEuFe4 As4 and CsEuFe4 As4 at high pressure, Phys. Rev. B 98, 014518 (2018)
  Jackson, D. E. and VanGennep, D. and Bi, W. and Zhang, D. and Materne, P. and Liu, Y. and Cao, G.-H. and Weir, S. T. and Vohra, Y. K. and Hamlin, J. J.
  
• Suppression of the magnetic order in CeFeAsO: Nonequivalence of hydrostatic and in-plane chemical pressure, Phys. Rev. B 98, 014517 (2018)
  Materne, P., and Bi, W. and Alp, E. E., and Zhao, J. and Hu, M. Y., and Jesche, A., and Geibel, C., and Kappenberger, R. and Aswartham, S., Wurmehl, S. and Büchner, B. and Zhang, D., and Goltz, T and Spehling, J. and Klauss, H.-H.
  
• Bandwidth controlled insulator-metal transition in BaFe2 S3 : A Mössbauer study under pressure, Phys. Rev. B 99, 020505(R) (2019)
  Materne, P. and Bi, W. and Zhao, J. and Hu, M. Y. and Amigó, M. L. and Seiro, S. and Aswartham, S. and Büchner, B. and Alp, E. E.