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- ItemSpecial Issue on Computational Ultrasound Imaging and Applications(Basel : MDPI, 2024) Nauber, Richard; Büttner, Lars; Czarske, Jürgen[No abstract available]
- ItemQuantenphysik in Klasse 9: Ergebnisse einer Akzeptanzbefragung für ein Spin-First-Unterrichtskonzept(Berlin : FU Berlin, 2023) Albert, Carsten; Pospiech, GescheQuantenphysik gilt als eines der herausforderndsten Themen bei der Vermittlung von Physik und ist gleichzeitig von herausragender Bedeutung bei künftigen technologischen Entwicklungen. Mit Blick auf den wachsenden Stellenwert der Quantenphysik innerhalb der schulischen Bildung wurde im Rahmen eines Design-Based-Research-Projektes ein Lehrkonzept entwickelt, das einen qualitativen und anknüpfungsfähigen Zugang zur Quantenphysik bereits in Klassenstufe 9 ermöglichen soll. Die Lerninhalte bauen dabei auf dem Elektronenspin als exemplarisches Zweizustandssystem auf. Mit dem Ziel einer ersten formativen Evaluierung wurden Akzeptanzbefragungen durchgeführt, um die Vermittlungsstrategie zu überprüfen und vor einer ersten Erprobung mit Schulklassen anzupassen. Die Interviews konnten zeigen, dass mit dem Ansatz die intendierten Inhalte überwiegend erfolgreich vermittelt werden können und dass ein weiterer Einsatz des Konzeptes im Rahmen von Feldstudien legitim erscheint. Außerdem gaben sie Hinweise und Impulse für erste Anpassungen am Konzept.
- ItemCoulomb exchange as source of Kitaev and off-diagonal symmetric anisotropic couplings(London : Springer Nature, 2024) Bhattacharyya, Pritam; Petersen, Thorben; Bogdanov, Nikolay A.; Hozoi, LiviuExchange underpins the magnetic properties of quantum matter. In its most basic form, it occurs through the interplay of Pauli’s exclusion principle and Coulomb repulsion, being referred to as Coulomb or direct exchange. Pauli’s exclusion principle combined with inter-atomic electron hopping additionally leads to kinetic exchange and superexchange. Here we disentangle the different exchange channels in anisotropic Kitaev–Heisenberg context. By quantum chemical computations, we show that anisotropic Coulomb exchange, completely neglected so far in the field, may be as large as (or even larger than) other contributions — kinetic exchange and superexchange. This opens new perspectives onto anisotropic exchange mechanisms and sets the proper conceptual framework for further research on tuning Kitaev–Heisenberg magnetism.
- ItemCorrelation induced magnetic topological phases in the mixed-valence compound SmB6(College Park, MD : APS, 2023) Liu, Huimei; Hirschmann, Moritz M.; Sawatzky, George A.; Khaliullin, Giniyat; Schnyder, Andreas P.SmB6 is a mixed-valence compound with flat f-electron bands that have a propensity to magnetism. Here, using a realistic Γ8 quartet model, we investigate the dynamical spin susceptibility and describe the in-gap collective mode observed in neutron scattering experiments. We show that as the Sm valence increases with pressure, the magnetic correlations enhance and SmB6 undergoes a first-order phase transition into a metallic antiferromagnetic state, whose symmetry depends on the model parameters. The magnetic orderings give rise to distinct band topologies: while the A-type order leads to an overlap between valence and conduction bands in the form of Dirac nodal lines, the G-type order has a negative indirect gap with weak Z2 indices. We also consider the spin polarized phase under a strong magnetic field, and find that it exhibits Weyl points as well as nodal lines close to the Fermi level. The magnetic phases show markedly different surface states and tunable bulk transport properties, with important implications for experiments. Our theory predicts that a magnetic order can be stabilized also by lifting the Γ8 cubic symmetry, thus explaining the surface magnetism reported in SmB6.
- ItemNaRuO2: Kitaev-Heisenberg exchange in triangular-lattice setting([London] : Nature Publishing Group, 2023) Bhattacharyya, Pritam; Bogdanov, Nikolay A.; Nishimoto, Satoshi; Wilson, Stephen D.; Hozoi, LiviuKitaev exchange, a new paradigm in quantum magnetism research, occurs for 90° metal-ligand-metal links, t2g5 transition ions, and sizable spin-orbit coupling. It is being studied in honeycomb compounds but also on triangular lattices. While for the former it is known by now that the Kitaev intersite couplings are ferromagnetic, for the latter the situation is unclear. Here we pin down the exchange mechanisms and determine the effective coupling constants in the t2g5 triangular-lattice material NaRuO2, recently found to host a quantum spin liquid ground state. We show that, compared to honeycomb compounds, the characteristic triangular-lattice cation surroundings dramatically affect exchange paths and effective coupling parameters, changing the Kitaev interactions to antiferromagnetic. Quantum chemical analysis combined with subsequent effective spin model simulations provide perspective onto the nature of the experimentally observed quantum spin liquid—it seemingly implies fairly large antiferromagnetic second-neighbor isotropic exchange, and the atypical proximity to ferromagnetic order is related to ferromagnetic nearest-neighbor Heisenberg coupling.