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A number of recent developments in the field of strongly correlated electron systems such as strange metal behaviour probed by new tools or detected in new settings, as well as new types of unconventional superconductors, including candidate topological superconductors—are creating a lot of excitement. Yet these developments have often taken place in isolation, with very limited cross-talk between these topics. This workshop seeks to discuss these topics under a common roof. The goal is to advance the understanding of complex materials and stimulate progress in adjacent fields.

Strange Metal Behaviour: One of the most exciting observations, made in an increasing number of very distinct settings, is strange metal behaviour. Its best-known manifestation is a (quasi) linear-in-temperature dc electrical resistivity, that defies description in terms of Landau quasiparticles of a Fermi liquid and, as a matter of fact, any quasiparticle description at all. However, other properties including thermodynamics, various spectroscopies, and quantum oscillation experiments, are being investigated and contain valuable extra information about the physics at play.

As an example, recent THz conductivity measurements on the canonical “strange metal” heavy fermion compound YbRh₂Si₂ revealed energy-over-temperature scaling with a critical exponent close to 1, thus identifying this behavior as associated with quantum critical charge fluctuations. This links to the charge localization seen in the cuprates near optimal superconductivity. It will be exciting to discuss how these findings relate to new candidate strange metals, including magic angle bilayer graphene.

Topological Superconductivity: The best-known examples of unconventional superconductivity include the cuprates, pnictides, organic conductors, and heavy fermion compounds. Among the latter are also several candidate spin triplet superconductors, or spin singlet superconductors coexisting with topological electronic states, that are of great interest for topological superconductivity. The recently discovery compound UTe₂ not only shows indications for chiral spin triplet pairing, but also for strange metal behaviour in its normal state. It will be illuminating to contrast its behaviour with that of the former key spin triplet candidate Sr₂RuO₄, that is a simple Fermi liquid in the normal state. Equally exciting is a flurry of recent observations that provide evidence for topologically superconducting surface states of FeTe_0.55Se_0.45. This material is close to optimal doping in the series FeTe_1-xSe_x. Recent studies have uncovered striking signatures of quantum criticality, both nematic and antiferromagnetic, as well as strange metallicity in the normal state near optimum superconductivity, both in this particular iron-chalcogenide series and in related iron-based systems.