Fermi-surface topology and emergence of novel electronic states in strongly corre-lated electron systems

• Applicants: Privatdozent Dr. Christoph Geibel; Professor Dr. Cornelius Krellner; Professor Dr. Clemens Laubschat; Professor Dr. Joachim Wosnitza; Professorin Dr. Gertrud Zwicknagl
• Subject Area: Experimental Condensed Matter Physics ; Theoretical Condensed Matter Physics
• Term: from 2016 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 316740996

• Final Report Year: 2023

Final Report Abstract

The project was dedicated to the study of the Fermi-surface topology and its interplay with quantum phase transitions in strongly correlated electronic systems. Complementary theoretical calculations were performed invoking both first-principles-based electronic structure and Kondo-like model Hamiltonians. Investigations have been carried out both on high-quality single crystals of already known f-electron compounds and organic materials as well as on the “new” heavy-fermion compound CeRh2As2. A rich diversity of Fermi-surface instabilities has been found in various critical phenomena. Of particular interest were transitions into states with novel orders involving magnetic, orbital, and charge degrees of freedom as well as the transition into the Fulde-Ferrell-Larkin-Ovchinnikov state. Key to the success was the close collaboration within the French-German consortium Fermi-NESt with its broad spectrum of techniques including sample preparation, experiments under extreme conditions, and material-specific theoretical simulations. This collaboration provided a classification of Fermi-surface instabilities within a coherent experimental and theoretical analysis. A number of unexpected results were encountered during the investigation. An example is the apparent existence of a “universal” temperature scale unrelated to the Kondo temperature for the Kondo-induced valence change in Yb-based compounds. A second one concerns the FFLO state in organic superconductors which appears as limiting case of an Abrikosov lattice with high-order vortices in the limit high magnetic fields parallel to the conducting layers. The greatest surprises, however, were encountered in the low-temperature properties of CeRh2As2. This material, which was first studied in the present consortium, exhibits multi-phase superconductivity and an ordered normal phase that probably involves quadrupolar degrees of freedom. The discovery of these unusual properties sparked interest and extensive research activities around the globe.

Publications

• Similar temperature scale for valence changes in Kondo lattices with different Kondo temperatures. Nature Communications, 9(1).
  Kummer, K.; Geibel, C.; Krellner, C.; Zwicknagl, G.; Laubschat, C.; Brookes, N. B. & Vyalikh, D. V.
  
• Divalent EuRh2Si2 as a reference for the Luttinger theorem and antiferromagnetism in trivalent heavy-fermion YbRh2Si2. Nature Communications, 10(1).
  Güttler, M.; Generalov, A.; Fujimori, S. I.; Kummer, K.; Chikina, A.; Seiro, S.; Danzenbächer, S.; Koroteev, Yu. M.; Chulkov, E. V.; Radovic, M.; Shi, M.; Plumb, N. C.; Laubschat, C.; Allen, J. W.; Krellner, C.; Geibel, C. & Vyalikh, D. V.
  
• Emerging 2D-ferromagnetism and strong spin-orbit coupling at the surface of valence-fluctuating EuIr2Si2. npj Quantum Materials, 4(1).
  Schulz, Susanne; Nechaev, Ilya A.; Güttler, Monika; Poelchen, Georg; Generalov, Alexander; Danzenbächer, Steffen; Chikina, Alla; Seiro, Silvia; Kliemt, Kristin; Vyazovskaya, Alexandra Yu.; Kim, Timur K.; Dudin, Pavel; Chulkov, Evgueni V.; Laubschat, Clemens; Krasovskii, Eugene E.; Geibel, Christoph; Krellner, Cornelius; Kummer, Kurt & Vyalikh, Denis V.
  
• Unexpected differences between surface and bulk spectroscopic and implied Kondo properties of heavy fermion CeRh2Si2. npj Quantum Materials, 5(1).
  Poelchen, Georg; Schulz, Susanne; Mende, Max; Güttler, Monika; Generalov, Alexander; Fedorov, Alexander V.; Caroca-Canales, Nubia; Geibel, Christoph; Kliemt, Kristin; Krellner, Cornelius; Danzenbächer, Steffen; Usachov, Dmitry Yu.; Dudin, Pavel; Antonov, Victor N.; Allen, James W.; Laubschat, Clemens; Kummer, Kurt; Kucherenko, Yuri & Vyalikh, Denis V.
  
• Field-induced transition within the superconducting state of CeRh2As2. Science, 373(6558), 1012-1016.
  Khim, S.; Landaeta, J. F.; Banda, J.; Bannor, N.; Brando, M.; Brydon, P. M. R.; Hafner, D.; Küchler, R.; Cardoso-Gil, R.; Stockert, U.; Mackenzie, A. P.; Agterberg, D. F.; Geibel, C. & Hassinger, E.
  
• Photo-emission signatures of coherence breakdown in Kondo alloys: dynamical mean-field theory approach. New Journal of Physics, 23(6), 063073.
  Poudel, B.; Lacroix, C.; Zwicknagl, G. & Burdin, S.
  
• Robust Fermi-Surface Morphology of CeRhIn5 across the Putative Field-Induced Quantum Critical Point. Physical Review Letters, 126(1).
  Mishra, S.; Hornung, J.; Raba, M.; Klotz, J.; Förster, T.; Harima, H.; Aoki, D.; Wosnitza, J.; McCollam, A. & Sheikin, I.
  
• Fermi surface of a system with strong valence fluctuations: Evidence for a noninteger count of valence electrons in EuIr2Si2. Physical Review B, 105(15).
  Götze, K.; Bergk, B.; Ignatchik, O.; Polyakov, A.; Kraft, I.; Lorenz, V.; Rosner, H.; Förster, T.; Seiro, S.; Sheikin, I.; Wosnitza, J. & Geibel, C.
  
• Orbital-induced crossover of the Fulde-Ferrell-Larkin-Ovchinnikov phase into Abrikosov-like states. Physical Review B, 106(6).
  Kotte, Tommy; Kühne, Hannes; Schlueter, John A.; Zwicknagl, Gertrud & Wosnitza, J.
  
• Possible Quadrupole Density Wave in the Superconducting Kondo Lattice CeRh2As2. Physical Review X, 12(1).
  Hafner, D.; Khanenko, P.; Eljaouhari, E.-O.; Küchler, R.; Banda, J.; Bannor, N.; Lühmann, T.; Landaeta, J. F.; Mishra, S.; Sheikin, I.; Hassinger, E.; Khim, S.; Geibel, C.; Zwicknagl, G. & Brando, M.