Neven Barišić

Noncentrosymmetric hexagonal Mn2P undergoes an antiferromagnetic transition at TN=104 K and exhibits a complex magnetic structure involving two crystallographically distinct Mn sites. An additional magnetic transition has recently been proposed below TN, although its microscopic origin remains unclear. Here, we investigate the electronic structure and its temperature dependence in Mn2P using soft X-ray photoelectron spectroscopy and X-ray absorption spectroscopy on high-quality single crystals. The Mn 2p core-level spectrum exhibits Mn2+-like spectral features. The valence-band spectrum shows a dominant Mn 3d contribution near the Fermi level, which is further examined by resonant photoelectron spectroscopy across the Mn L2,3 absorption edges. The resonant enhancement confirms that Mn 3d states contribute substantially across the 0-7 eV valence-band region. Neither the core-level nor the valence-band spectra exhibit significant temperature dependence across the magnetic transitions, suggesting that the magnetic phase transitions do not involve a discernible change in the Mn valence or local spin state.

Murunskite (K₂FeCu₃S₄) is a layered sulfosalt chalcogenide that occupies a unique position between the cuprate and iron pnictide families: it shares electronic characteristics with the former and adopts the crystal structure of the latter. Despite a completely random distribution of magnetic Fe within a nonmagnetic Cu matrix, murunskite exhibits a well-defined quarter-zone antiferromagnetic transition at 97 K and complete orbital order below 30 K. These findings reveal the unexpected emergence of long-range order in a high-entropy-like environment. This inherent robustness to site disorder in a layered structure makes murunskite a paradigmatic system for further studies. Here, we investigate doping strategies in murunskite to assess how its electronic and magnetic properties can be tuned. Using melt-growth techniques, we achieve substitutions at the magnetic metal site (Fe), spacer cation (K), and sulfur ligand (S), which significantly influence transport and magnetic properties. In addition, we use ionic-liquid gating on the parent compound and observe a gate-dependent suppression of resistivity, confirming the potential for electrostatic control over transport. Our results demonstrate the chemical and electronic plasticity of murunskite, offering a valuable platform for co-engineering disorder, magnetism, and transport, and opening avenues to explore quantum phenomena in correlated and high-entropy materials.

The magnetic response of magnetite as it cycles through the Verwey transition at ca. 120 K is still not completely described despite numerous studies of both structural and magnetic domains. For example, although alternating current susceptibility increases upon heating across the Verwey temperature TV, the magnetization may either increase or decrease (up and down step). Since many intertwined processes take place at the TV, the nature of magnetic changes viewed in a multifaceted way may clarify the nature of these processes and how to use particulars of the transition as a diagnostic tool. To this aim, we report measurements on the magnetic response of magnetite upon heating across TV under a wide range of applied field environments. Studied samples include synthetic, stoichiometric, and doped (Zn, Ti, and Al) single crystals, as well as a natural polycrystalline sample. We proposed the explanation of the step direction in magnetic moment vs. T at TV. We also found that the change of monoclinic c axis triggered by magnetic fields may widen transition region primarily in stoichiometric magnetite. These findings add to better understanding the mechanism of the transition.

Murunskite K ₂ Cu ₃ FeS ₄ is a representative sulfosalt, isostructural to the pnictides, but with electronic properties more similar to the insulating parent compounds of the cuprates. We use it as a bridge to compare the chemical and physical roles of metal and ligand orbitals in cuprates and pnictides. In cuprates, ionicity, covalency, and metallicity are tightly interwoven to give rise to high-temperature superconductivity (SC). Their most remarkable property is the interaction of an ionically localized hole on the copper (Cu) with a Fermi liquid (FL) on the oxygens (O), which is critically important for understanding all key properties of these materials. The localization is due to strong correlations on the Cu 3 d orbital. We describe a scenario in which the localized hole gives rise both to SC by Cooper scattering of O holes, and to Fermi arcs, as observed in cuprate spectroscopy, the latter by a purely kinematic projection of the static local disorder, without invoking any residual interactions between the mobile O FL carriers. In the pnictides, the orbitals responsible for binding and metallic conduction appear to be separate. The Fe 3 d e _g orbitals hybridized with the ligands set the lattice spacing. The 3 d t 2 g orbitals overlap directly between the Fe atoms, resulting in several electronic bands appearing at the Fermi level. The ensuing FL exhibits both charge and magnetic correlations. We argue that a similar SC scenario as in the cuprates is plausible in the pnictides, except that a light FL scatters on a slow nearly-antiferromagnetic (AF) one, rather than on localized holes as in the cuprates. In murunskite, the greater covalency of sulfur orbitals compensates for total disorder in the Fe atom positions, giving rise to an agglomeration of fractal magnetic clusters coexisting with perfect crystallographic order and exhibiting surprisingly robust quarter-zone AF. Because the open ligand orbitals play an important role in it, the essentially local quarter-zone AF of murunskite is more similar to the SC of the cuprates than to the half-zone AF of the pnictides, in which the ligands are passive.

In 2025, the Year of Quantum Science and Technology ( https://quantum2025.org/ ), we celebrate a century of quantum mechanics, witnessing a surge in activities that illuminate its inherent strangeness and drive technological innovation. Superconductivity, discovered 114 years ago, stands as a prime example, offering direct and compelling evidence of macroscopic quantum phenomena. Beyond its ability to conduct immense currents without loss, superconductivity reveals the quantum realm operating on a scale we can directly observe and manipulate. The macroscopic quantum coherence, where an ensemble of particles is described by a single wave function, leads to remarkable consequences: dissipation-less current and flux quantization—the basic properties exploited in superconducting quantum circuit fabrication. This Roadmap has been inspired by intensive discussions and collaborations emerging from the European Cooperation in Science & Technology COST-Action CA21144 (SuperQuMap—Superconducting Nanodevices and Quantum Materials for Coherent Manipulation). The aim of the COST Action SuperQuMap is to establish a strong European network centered on macroscopic quantum behavior in superconductors, bringing together groups of different backgrounds and more than 30 countries. The roadmap outlines the network’s concrete activities, driving advancements in superconductor-based quantum technologies and charting future directions. Spanning fundamental research to practical applications, the roadmap incorporates insights from industry partners developing quantum computation. It begins by exploring quantum materials, highlighting how topology and electronic correlations could catalyze a quantum leap in technology. We then delve into manipulating the superconducting phase, leveraging advancements in magnetism, 3D fabrication, and tunable correlations. Further, we showcase the advanced microscopy techniques—such as angle-resolved photoemission spectroscopy and scanning probes—used to visualize quantum behavior. Finally, and crucially, we detail the quantum devices developed within the network, and their transformative impact on modern quantum computing approaches.

We find a strongly enhanced entanglement within the pseudogap regime of the Hubbard model. This entanglement is estimated from the quantum Fisher information and, avoiding the ill-conditioned analytical continuation, the quantum variance. Both are lower bounds for the actual entanglement and can be calculated from the (antiferromagnetic) susceptibility, obtained here with the dynamical vertex approximation. Our results qualitatively agree with experimental neutron scattering experiments for various cuprates. Theory predicts a ln ( 1 / T ) divergence of the entanglement for low temperatures T , which is however cut off by the onset of superconductivity.

α-Ir₂B_3−x and β-Ir₂B_3−x exhibit strong interactions between Ir and B; however, β-Ir₂B_3−x demonstrates a negligible covalent bonding component in the boron subunits compared to strong covalent bonding in the chair-like boron hexagons of α-Ir₂B_3−x.