Strongly correlated electron systems studied by strain-dependent angle-resolved photoemission spectroscopy

• Applicant: Dr. Heike Pfau
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2018 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 414152718

The foundation of all modern technology is the power of quantum theories to predict mechanical, optical and electrical properties with high precision. Common metals and semiconductors like copper or silicon are well described by band theories. In contrast, understanding the interactions that lead to the remarkable properties of strongly correlated electron materials such as high-temperature superconductivity remains deeply challenging. The coupling of spin, orbital and lattice degrees of freedom in strongly correlated electron systems leads to complex phase diagrams with intertwined or competing orders. Understanding such phase diagrams is essential for formulating effective quantum theories.Angle-resolved photoemission spectroscopy (ARPES) has contributed profoundly to our understanding of correlated materials by accessing the electronic band structure directly. However, ARPES is incompatible with common non-thermal tuning parameters like magnetic fields, electric fields, or pressure. Since these tuning parameters build-up phase diagrams, the microscopic information from ARPES is often missing.My goal is to combine anisotropic strain as a quantitative, non-thermal tuning parameter with ARPES and add electronic structure information to the phase diagram of quantum materials. I have developed a prototype of a strain apparatus for APRES and performed first successful tests. My proposal aims at employing this new technique to study iron-based superconductors and strontium ruthenate. Their thermodynamic and transport properties can be tuned by anisotropic strain, which makes them prime candidates. The nematic susceptibility in iron-based superconductors derived from strain-dependent ARPES will substantially contribute to identify the driving order parameter of the nematic phase, its interplay with superconductivity and possible quantum critical behavior. Strontium ruthenate is one of the few materials discussed in terms of odd-parity superconductivity and I will be able to shed light on its superconducting order parameter. These studies will considerably improve our understanding of the phase diagrams of these two materials. They will also feedback to the improvement of the current strain apparatus and establish it as a well characterized tuning device for ARPES in strongly correlated materials.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Sung-Kwan Mo