Mini-symposium: Current Topics in Superconductivity

  • Datum: –17.30
  • Plats: Zoom: https://uu-se.zoom.us/j/67457126795
  • Föreläsare: Jorge Cayo, Andreas Kreisel och Jörg Schmalian
  • Kontaktperson: Peter Oppeneer
  • Seminarium

 Programme

16:00 – 16:30 Jorge Cayo

Odd-frequency pairing in systems with conventional superconductivity

 

16:30 – 17:00 Andreas Kreisel

Quasiparticle Interference in Sr2RuO4: Spectroscopy of the van Hove singularities and the superconducting order parameter

 

17:00 – 17:30 Jörg Schmalian

Quantum critical Eliashberg theory and its holographic dual

 

ABSTRACTS

Jorge Cayo, Uppsala University

Odd-frequency pairing in systems with conventional superconductivity

Odd-frequency superconducting pairing represents a truly unconventional phenomenon where pair correlations are odd in relative time and, hence, inherently non-local in time. In this talk I will discuss how this type of pairing emerges in junctions and bulk systems by simply using conventional s-wave superconductors. I will conclude by pointing out some possible detection protocols of this exotic superconducting pairing.

 

Andreas Kreisel, Leipzig University

Quasiparticle Interference in Sr2RuO4: Spectroscopy of the van Hove singularities and the superconducting order parameter

The single-layered ruthenate Sr2RuO4 is one of the most enigmatic unconventional superconductors. While for many years it was thought to be the best candidate for a chiral p-wave superconducting ground state, desirable for topological quantum computations, recent experiments suggest a singlet state, ruling out the original p-wave scenario. It seems that the superconductivity as well as the normal state properties of the multi-layered compounds of the ruthenate perovskites are strongly influenced by a van Hove singularity in proximity of the Fermi energy. Tiny structural distortions at the surface of the material move the van Hove singularity across the Fermi energy with dramatic consequences for the physical properties.

In this seminar a theoretical model for the electronic structure of the surface layer of Sr2RuO4 exhibiting multiple van Hove singularities is presented and consequences for the tunneling process in scanning tunneling spectroscopy experiments are discussed by comparing theoretically calculated quasiparticle interference maps with experimentally available data. It is demonstrated that the detection of the gamma band is facilitated through the octahedral rotations in the surface layer. Finally, it is shown what can be learned about the superconducting order parameter from STM experiments where the superconducting state can be imaged.

 

Jörg Schmalian, Karlsruhe Institute of Technology

Quantum critical Eliashberg theory and its holographic dual

Superconductivity is abundant near quantum-critical points, where fluctuations suppress the formation of Fermi liquid quasiparticles and the Bardeen-Cooper-Schrieffer theory no longer applies. Two very distinct approaches have been developed to address this issue: quantum-critical Eliashberg theory and holographic superconductivity. The former includes a strongly retarded pairing interaction of ill-defined fermions, the latter is rooted in the duality of quantum field theory and gravity theory. We demonstrate that both are different perspectives of the same theory. We derive holographic superconductivity in form of a gravity theory with emergent space-time from a quantum many-body Hamiltonian - the Yukawa SYK model - where the Eliashberg formalism is exact. Exploiting the power of holography, we then determine the dynamic pairing susceptibility of the model. Our holographic map comes with the potential to use quantum gravity corrections to go beyond the Eliashberg regime.