Periodic Reporting for period 4 - ExQuiSid (Extreme Quantum Matter in Solids)
Okres sprawozdawczy: 2022-12-01 do 2024-05-31
Quantum stochastic processes in solids, representing many-body systems par excellence, are believed to lead to extreme forms of quantum entanglement and non-local correlations denoted extreme quantum matter, that offer a well-defined starting point for an understanding of a wide range of anomalous materials properties, as well as emergent electronic phases such as magnetically mediated superconductivity or partial spin and charge order. While a large body of experimental evidence seems to suggest a breakdown of traditional concepts such as well-defined quasi-particle excitations, present-day disagreement between experiment and theory may be traced to the lack of experimental information on the spectrum of low-lying excitations close to and far from equilibrium under controlled conditions. The objectives of ExQuiSid are systematic experimental studies to identify novel forms of quantum phase transitions and quantum matter, and to search for quantum dynamical phases under periodic drive.
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.
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.
ExQuiSid advances the understanding of the nature of extreme quantum matter in the most extensively studied model systems, notably simple magnetic materials (insulators and metals) tuned through a quantum phase transition. For the studies carried out in ExQuiSid a new generation of experimental methods was implemented comprising neutron spectroscopy with an unprecedented energy resolution even under large magnetic fields, transverse-field vector magnetometry, calorimetry and transport down to milli-Kelvin temperatures, and, ultra-high purity single-crystal growth combined with advanced materials characterisation.
ExQuiSid resolved long-standing mysteries in model-systems of textbook quantum phase transitions, enabled studies on the creation, nature and classification of non-equilibrium quantum matter in solids at ultra-low energies and temperatures. It also enabled studies of quantum matter driven periodically out of equilibrium in the search for dynamical quantum instabilities and dynamical quantum phases.
ExQuiSid resolved long-standing mysteries in model-systems of textbook quantum phase transitions, enabled studies on the creation, nature and classification of non-equilibrium quantum matter in solids at ultra-low energies and temperatures. It also enabled studies of quantum matter driven periodically out of equilibrium in the search for dynamical quantum instabilities and dynamical quantum phases.