Matjaž Gomilšek

The quantum behavior of light particles in solids gives rise to phenomena that cannot be captured by a classical description. We show that muon spin spectroscopy ( μ SR ), when paired with a quantum-mechanical treatment of the implanted muon, becomes a sensitive and direct probe of nuclear quantum effects. By modeling the muon as a spatially extended quantum particle, our approach captures strong anharmonic behavior. We demonstrate this in Zn-barlowite, which serves as a nontrivial test case due to its structurally complex lattice and the presence of both fluorine and hydroxyl groups. Our results establish a route for extracting nuclear quantum signatures from μ SR data and open different opportunities for studying light nuclei such as hydrogen and lithium in systems where quantum fluctuations shape structure and function.

Biofilm-associated contamination represents a persistent and costly challenge across environmental systems, causing reduced efficacy of disinfectants. Recently, nanobubbles (NBs) have shown promise for biofilm decontamination; yet, their underpinning mode of action remains a topic of debate. In this study, the interaction of air-generated NBs with Escherichia coli and Staphylococcus aureus biofilms was investigated. NBs were generated using a venturi nozzle and characterized using Nanoparticle Tracking Analysis, revealing a NB density of 5.66 × 10⁸ particles/mL and a mean diameter of 84 nm. Application of NB solution to microbial biofilms resulted in a 2.16 log reduction for E. coli and 1.52 log reduction for S. aureus, along with visible morphological changes such as cell collapse, wrinkling, and matrix disruption. ESR spin trapping confirmed hydroxyl radical formation, but intracellular ROS and lipid peroxidation levels were minimal and, in some cases, not significantly different from Milli-Q water controls. After 28 days, NBs remained present and continued to demonstrate antimicrobial activity, biofilm disruption, and some ROS activity. These findings indicate that although hydroxyl radicals are generated, oxidative stress is not the dominant antimicrobial mechanism under the examined conditions, suggesting physical biofilm disruption is the primary mode of action.

Strong correlations and ferromagnetic Hund's coupling lead to diverse electronic phenomena in transition-metal oxides that sensitively depend on the d-orbital electron filling. Fullerides, their p-electron counterparts, exhibit effective antiferromagnetic Hund's coupling in a different energy range. At half-filling (n = 3, three electrons in triply degenerate orbitals), both d- and p-electron systems are Mott insulators due to strong correlations and Hund's coupling. Away from half-filling, in single-electron/hole (n = 1,5) d-orbital systems, Hund's coupling opposes the correlations, reducing the Mott gap and allowing survival of metallicity. Here we report a single-hole multiorbital correlated p-electron system, orthorhombic-structured Yb₂CsC₆₀ comprising pentavalent C₆₀^5- anions, which also exhibits a robust metallic state with no Mott transition, just like in the metastable single-electron cubic-structured CsC₆₀. We assert that particle-hole symmetry holds well in (n = 1,5) fullerides and that their p-electron-derived states are analogous to those in d-orbital solids, providing impetus for further study of these correlated systems.

Quantum spin chains with competing interactions offer a platform where low dimensionality and frustration—both acting to suppress magnetic order—intersect. We studied magnetic ordering in the spin- 1 2 chain compound AgCuVO 4 using muon spin spectroscopy and neutron diffraction. Long-range magnetic order emerges at T N = 2.0 ( 1 ) K , which is ∼ 1 / 200 of the dominant intrachain coupling J and ∼ 1 / 15 of the interchain interactions. The collinear incommensurate amplitude-modulated magnetic structure features a reduced ordered moment of 0.13 ( 3 ) µ B , confined to the a b plane and modulated along the c axis—perpendicular to the spin chains—indicating frustrated interchain couplings. The low T N , small moment, and incommensurate order highlight strong frustration, positioning AgCuVO 4 as a model system for exploring frustration in quantum spin chains.

The unabating discovery of nanoskyrmions in centrosymmetric magnets challenges the conventional Dzyaloshinskii-Moriya (DM) skyrmion stabilization mechanism. We investigate Gd 2 PdSi 3 using polarized resonant x-ray scattering and find that the low-field incommensurate modulations are elliptical helices, evolving into spin-density waves at higher fields. Quasi-2D magnetism arises via local DM interactions generated by inversion symmetry breaking around Gd-Gd bonds, which we characterize using atomistic simulations. Our findings suggest a prominent “hidden” role of DM interactions even in centrosymmetric skyrmionic hosts.

Centrosymmetric GdRu 2 Si 2 exhibits a variety of multi- Q magnetic states as a function of temperature and applied magnetic field, including a square skyrmion-lattice phase. The material's behavior is strongly dependent on the direction of the applied field, with different phase diagrams resulting for fields applied parallel or perpendicular to the crystallographic c axis. Here, we present the results of muon-spin relaxation ( μ + SR ) measurements on single crystals of GdRu 2 Si 2 . Our analysis is based on the computation of muon stopping sites and consideration of quantum zero-point motion effects of muons, allowing direct comparison with the underlying spin textures in the material. The muon site is confirmed experimentally, using angle-dependent measurements of the muon Knight shift. Using transverse-field μ + SR with fields applied along either the [001] or [100] crystallographic directions, we distinguish between the magnetic phases in this system via their distinct muon response, providing additional evidence for the skyrmion and meron-lattice phases, while also suggesting the existence of RKKY-driven muon hyperfine coupling. Zero-field μ + SR provides clear evidence for a transition between two distinct magnetically ordered phases at 39 K.

Skyrmions are particlelike vortices of magnetization with nontrivial topology, which are usually stabilized by Dzyaloshinskii-Moriya interactions (DMI) in noncentrosymmetric bulk materials. Exceptions are centrosymmetric Gd- and Eu-based skyrmion-lattice (SL) hosts with zero DMI, where both the SL stabilization mechanisms and magnetic ground states remain controversial. We address these here by investigating both the static and dynamical spin properties of the centrosymmetric SL host Gd 2 PdSi 3 using muon spectroscopy. We find that spin fluctuations in the noncoplanar SL phase are highly anisotropic, implying that spin anisotropy plays a prominent role in stabilizing this phase. We also observe strongly anisotropic spin dynamics in the ground-state (IC-1) incommensurate magnetic phase of the material, indicating that it hosts a meronlike multi- q structure. In contrast, the higher-field, coplanar IC-2 phase is found to be single q with nearly isotropic spin dynamics.

Nothing can ever be perfectly still, no matter how cold you make it. Take solid nitrogen, for example, which freezes at a bone-chilling -210 °C. You might expect its molecules to be frozen rigidly in place but, even at such extreme temperatures, they have a life of their own. At the microscopic level, quantum effects become important and random fluctuations ensure that molecules of solid nitrogen will jitter unceasingly. In the limit of absolute zero temperature, these tiny movements can have a considerable influence on the properties and behaviour of whole materials. New work published by a collaboration of scientists from Slovenia and the UK has sought to develop a better understanding of the effects of this quantum motion. Nick Martin from Vodanube LLC, and his colleagues have applied Probabilistic Risk Assessment (PRA) to flood inundation. Their research optimises current adaptation and future mitigation strategies, even while acknowledging PRA’s limitations. The team demonstrates how this approach can guide more resilient water resource management, and highlights opportunities for further study.

Frustration in magnetic materials arising from competing exchange interactions can prevent the system from adopting long-range magnetic order and can instead lead to a diverse range of novel quantum and topological states with exotic quasiparticle excitations. Here, we review prominent examples of such emergent phenomena, including magnetically-disordered and extensively degenerate spin ices, which feature emergent magnetic monopole excitations, highly-entangled quantum spin liquids with fractional spinon excitations, topological order and emergent gauge fields, as well as complex particle-like topological spin textures known as skyrmions. We provide an overview of recent advances in the search for magnetically-disordered candidate materials on the three-dimensional pyrochlore lattice and two-dimensional triangular, kagome and honeycomb lattices, the latter with bond-dependent Kitaev interactions, and on lattices supporting topological magnetism. We highlight experimental signatures of these often elusive phenomena and single out the most suitable experimental techniques that can be used to detect them. Our review also aims at providing a comprehensive guide for designing and investigating novel frustrated magnetic materials, with the potential of addressing some important open questions in contemporary condensed matter physics.