Flat bands and high-order Van Hove singularities

The event FB-VHS 2024 was divided into a workshop week during May 27 – 31, 2024 and a following seminar week June 3 - 7, 2024.  The first week was held in a novel format with participants meeting in two nodes in Daejeon, Korea, and in Dresden, Germany. Talks and question sessions were broadcasted life from each node. The workshop and seminar brought together scientists from experiment and theory working on the engineering, description, and consequences of flattened electronic bands, which can range from high-order Van Hove points to completely flat bands with or without topological character. In doing so, the aim of the workshop was to advance the field of quantum design of materials.

The workshop allowed the participants to approach the common theme of band flatting from different viewpoints. On the one hand, this means studying realisations in different material platforms such as correlated electron systems, designer heterostructures, or magnetic materials. On the other hand, this involves utilising different methodologies from material synthesis and experimental techniques, over ab initio predictions and modelling, to topological analyses and many-body methods.  

Over 70 participants from 12 countries attended the meeting from the Dresden node, with many more from the Daejeon node. The program included 50 invited talks, as well as two poster sessions, and ample time for discussion and collaboration. The focus of the first week was on presenting new results, while the second week emphasised collaborative aspects. During the workshop, several exciting results were presented on, e.g., quantum geometric effects by Youichi Yanase and Raquel Queiroz, on fractional quantum anomalous Hall states by Xiadong Xu, Nicolas Regnault, and Andrei Bernevig, on latest developments in twisted graphene structures by Eva Andrei, Shahal Ilani, and Siddharth Parameswaran, as well as non-twisted graphene systems by Andrei Chubukov and Thomas Weitz, on electronic mechanisms for superconductivity by Francesco Guinea and Jörg Schmalian, and on tuning correlated states around Van Hove singularities in kagome metals and strontium ruthenate by Haim Beidenkopf and Andrew Mackenzie.  Many more high-level talks on relevant topics were given both by established experts and junior researchers in their field. All early-career researchers were invited to present a poster, and the poster sessions were well attended with lively discussions.

Overall, the intense exchange between participants from different sub-fields, both locally and between nodes, created a stimulating atmosphere.

The talks, discussions, and posters at FB-VHS 2024 demonstrated the rapid development in the field of correlated electrons in flat or flattened bands with promising prospects due to evolving experimental tuning techniques and theoretical methods. As a result, the workshop enabled advances in the direction of deliberate control over Van Hove singularities and band flattening in correlated electron systems, and the stabilization of novel ground states.

We would like to thank the wonderful team of the Max Planck Institute for the Physics of Complex Systems, as well as the IBS Center for Theoretical Physics of Complex Systems, for their excellent assistance and technical support.