Department of Physics • University of Cologne

The recent discovery of the family of AV3Sb5 (A=K, Cs, Rb) metals has sparked great interest in the study of kagome lattice systems. These materials exhibit a plethora of intriguing low-temperature behaviour, as superconductivity, a charge density wave (CDW) and time-reversal symmetry breaking (TRSB) without magnetic ordering have all been found within these compounds. Although much effort has been devoted to understanding the physics of these materials in the last few years, there are still many unknowns. For instance, the nature of TRSB is still unclear, as is the mechanism that stabilizes the CDW found. In this work, we study a model of interacting electrons on the kagome lattice at a mean-field level. In particular, both a single-orbital model and a multi-orbital extension are considered. Our calculations reveal the presence of different interaction-driven CDW patterns, with the single-orbital model exhibiting a CDW phase compatible with the experimental findings. Furthermore, no traces were found of TRSB without magnetic ordering nor of ferromagnetism, in accordance with recent variational Monte Carlo calculations. Our results also suggest that the px and py orbitals of the in-plane Sb atoms might not be crucial for determining the physical properties of AV3Sb5 materials, while the van Hove singularities in the band structure could be playing a key role in this regard.

Improving the understanding of pedestrian crowd dynamics is a growing field with essential contributions from many areas of science utilizing empirical data and mathematical models. Pedestrians systems exhibit a number of self-organization phenomena like lane formation and temporal clogging which are interesting from a physics perspective. Simulations of these scenarios can improve the understanding of these phenomena by focusing on minimal models that can reproduce the observations. Many of these phenomena in pedestrian dynamics are not unique to the system and are observed in related fields like granular materials, colloids, and active matter. The presented work introduces methods from solid-state physics and granular matter to quantify the spatial order of pedestrian systems. The focus is on bottleneck flow when a crowd has to pass a spatially restricted area (e.g., a door leading to a hall), a crucial scenario in pedestrian dynamics and the flow of granular matter.

A fundamental distinction between many-body quantum states are those with short- and long-range entanglement (SRE and LRE). The latter, such as cat states, topological order, or critical states cannot be created by finite-depth circuits. Remarkably, examples are known where LRE is obtained by performing single-site measurements on SRE states such as preparing the toric code from measuring a sublattice of a 2D cluster state. I will present a general framework of how and why these known protocols give rise to long range entanglement based on interpreting the cluster state measurement as implementing the non-local Kramers-Wannier transformation. This provides a scalable and practical way to 'gauge' a symmetry using only finite-depth circuits and measurements, and moreover allows us to go beyond the preparation of stabilizer states. In addition, we find a complexity hierarchy on long-range entangled states based on the minimal number of measurement layers required to create the state. I will argue that certain phases of matter cannot be prepared using any finite number of layers, while remarkably certain non-Abelian topological orders can be prepared in a single round of measurement. As an application, I will outline how current NISQ devices, such as Rydberg atom arrays and Google's quantum processors, can scalably prepare a large class of exotic phases such as non-Abelian topological order and even fracton phases. This talk is based on 2112.01519, 2112.03061, 2209.03964, and 2209.06202

We study electronic transport in Weyl semimetals with spatially varying nodal tilt profiles. We find that the flow of electrons can be guided precisely by judiciously chosen tilt profiles. In a wide regime of parameters, we show that electron flow is described well by semiclassical equations of motion similar to the ones governing gravitational attraction. This analogy provides a physically transparent tool for designing tilt-tronic devices, such as electronic lenses. The analogy to gravity circumvents the notoriously difficult full-fledged description of inhomogeneous solids, but a comparison to microscopic lattice simulations shows that it is only valid for trajectories sufficiently far from analogue black holes. We finally comment on the Berry curvature-driven transverse motion and relate the latter to spin precession physics. arXiv:2210.16254