The ERC project ExQuiSid focusses on the experimental investigation of quantum correlations and quantum entanglement in materials with strong electronic correlations under extreme conditions (ultra-low temperatures, high magnetic fields and high pressures). To resolve the nature and relevance of quantum correlations and quantum entanglement in real materials, the methodology comprises materials preparation with measurements of bulk and transport properties and neutron and x-ray spectroscopy.
Selected major results of ExQuiSid include:
First observation of long-range topologically non-trivial magnetic order (a skyrmion lattice) as a generic ground state in the zero-temperature limit with a second skyrmion lattice phase at high temperatures due thermal fluctuations akin order by disorder. This demonstrated the possible existence of quantum phase transitions between topologically trivial and non-trivial states as a new field of research for the future.
Discovery of quantum phase transitions of mesoscale textures under carefully controlled studies of the transverse-field quantum phase transition in an Ising ferromagnet under tilted fields. This observation represents the starting point for a new field of research, focusing on the entanglement of mesoscale systems and the formation of dynamical quantum phases under periodic drive.
Discovery of symmetry-enforced topological nodal planes in chiral magnets, permitting to control topological crossings of electronic and bosonic band structures by virtue of symmetry breaking perturbations. Identification of topological protectorates of the Fermi surface, and large Berry curvature contributions in a variety of transport properties. As nodal planes are generic in many space groups, they motivate extensive studies towards putative applications.
Discovery of quantum oscillations of the quasi-particle lifetime. Representing a generic effect beyond the classical Onsager mechanism, quantum oscillations of the quasiparticle lifetime promise direct microscopic evidence of many-body interactions and quantum coherence in metals. Having confirmed the initial observations in further materials, this discovery promises to be the starting point for the discovery of new forms of electronic order.
Observation of the emergence of a topological magnon band structure born out of the non-trivial topology of spin structures in real space using comprehensive neutron spectroscopy. Featuring Landau quantization akin the well-known effects in metals, the topological magnon bands are inherently different to conventional magnon band structures, suggestive of edge channels and more complex non-reciprocal spin transport. Representing a new field of research on topological band structures amenable for applications in quantum technologies.
