Materials with a kagome lattice host exotic quantum phenomena driven by the interplay between band topology, spin-orbit coupling, magnetism, and electronic correlations. While the magnetism of kagome materials has been widely investigated, their unconventional superconductivity (SC) remains largely unexplored due to the limited availability of suitable materials. Here, we report evidence of unconventional SC in the ScIr 2 - x Si x family by combining muon-spin spectroscopy measurements with band-structure calculations. The parent ScIr 2 undergoes a structural phase transition from a high- T cubic- to a low- T rhombohedral phase, while the Ir kagome layer remains, albeit slightly, distorted. Although the structural transition is suppressed by Si substitution, the superconducting pairing of ScIr 2 - x Si x remains well described by a two-gap model. Since at least one of the gaps exhibits nodes, this indicates an unconventional SC. Its unconventional nature can be explained by the distinct flat bands occurring near the Fermi level, leading to strong electronic correlations in the ScIr 2 - x Si x family. Moreover, the low- T phase of ScIr 2 exhibits an Ir chiral chain; therefore, it can be classified as a topological chiral crystal. Overall, the unusual properties of the ScIr 2 - x Si x family make it an interesting, albeit rare, system for studying the interplay between unconventional SC, flat bands, and chirality.

Kagome lattices host exotic phenomena such as quantum spin liquids, topological Weyl nodes, and flat bands. The kagome ferromagnet Co3Sn2S2 has been a focus of debate due to conflicting reports on its magnetic character. Here, using weakly perturbative probes—primarily neutron scattering and Mössbauer spectroscopy—we determine its ground state and magnetic Hamiltonian. The spin wave spectrum is reproduced by a simple Hamiltonian dominated by a large in-plane nearest-neighbor Heisenberg interaction J and an antisymmetric Dzyaloshinskii-Moriya interaction that is roughly one third of J. This Hamiltonian yields a canted, noncollinear ferromagnetic ground state with an umbrella-type structure, which our data show to be the true ground state at all temperatures below TC. Additionally, the spin susceptibility above TC exhibits a reduced critical exponent, akin to other spin-anisotropic systems. Our findings explain the unconventional magnetism in Co3Sn2S2, including the giant anomalous Hall effect and the origin of chiral phonons. The magnetic ground state of the kagome magnet Co3Sn2S2 has been the subject of numerous recent studies. Here, the authors study the ground state and magnetic Hamiltonian of Co3Sn2S2 and provide results consistent with a canted umbrella structure and a large Dzyaloshinskii-Moriya interaction term.

Low-dimensional materials manifest structural anisotropy, quantum confinement, and tightly bound excitonic states, which make them attractive building blocks that can be assembled within three-dimensional laterally stitched heterostructures, stacked van der Waals solids, and complex moiré superlattices. Ion intercalation in the galleries between layered materials provides a means of modifying interlayer separation and coupling, but it is also known to drive the shearing of the layers. In this article, we explore the distinct ligand coordination environments afforded by vanadyl oxygens of singular [V4O10] sheets and examine how the size, polarizability, and stoichiometry of Group I cations sandwiched between such layers determine the interlocking of the sheets in stacked structures. Based on the topochemical insertion of alkali-metal ions into the layered λ-V2O5, we identify seven types of guest ion coordination sites discretized into four distinct regimes of interlayer shear in units of half octahedral widths. The coordination preferences of intercalated cations govern how they interlock 2D [V4O10] sheets and engender specific shear conformations. We present evidence that static and dynamic disorder in guest ion arrangement modulate the magnetic structure of the intercalated compounds based on electrostatic polarization, localization of charge and spin density, and lattice distortion. The results illustrate the use of topochemical ion insertion to modulate stacking relationships and magnetic transition characteristics.

The observation of pressure-induced superconductivity in two- and three-layer Ruddlesden-Popper nickelates has spurred intense interest in these materials as a platform for exploring unconventional superconductivity. While the ground state of these systems has been shown to exhibit magnetism, the direct determination of their magnetic structure remains elusive. This is a crucial aspect, as magnetism may play a role in the pairing mechanism of superconductivity in these materials. In this study, we resolve the magnetic structures in the bilayer (2222) polymorphs of La_{3}Ni_{2}O_{7} and La_{2}PrNi_{2}O_{7} compounds, using a combination of complementary techniques, namely, neutron powder diffraction and muon-spin rotation/relaxation (μSR). Magnetic neutron scattering in both samples emerges below ∼150 K and is observed at the (q_{x},1/2,0) position, with q_{x}=0 and 1/2 for La_{3}Ni_{2}O_{7} and q_{x}=0 for La_{2}PrNi_{2}O_{7}. Alternating low-magnetic-moment (0.05–0.075μ_{B}) and high-magnetic-moment (0.66μ_{B}) stripes form a single layer; the bilayers are formed through antiferromagnetic stacking of single layers along the out-of-plane direction. The magnetic scattering with two propagation vectors q_{x}=0 and 1/2 in the undoped La_{3}Ni_{2}O_{7} is attributed to two magnetic stacking polymorphs within a single crystallographic phase. The magnetic structures are substantiated by the μSR spectra. These findings provide a detailed understanding of the magnetic ground state in bilayer nickelates, offering crucial insights into the possible precursor states that may influence the emergence of superconductivity in these materials.

MgB4O7:Ce, Li has emerged as a promising candidate for optically stimulated luminescence dosimetry (OSL) due to its high sensitivity to ionizing radiation, fast luminescence, and extended linear dose-response range. Despite its potential, variations in fading behavior and discrepancies in the linear dose-response region reported in the literature, compounded by a lack of direct sensitivity comparisons across studies, have raised questions regarding the reproducibility of the synthesis. These inconsistencies are believed to stem from differing synthesis methods. Our study integrates X-ray diffraction, synchrotron X-ray absorption spectroscopy, and comprehensive thermoluminescent (TL) and OSL analyses to demonstrate that the choice of starting reagents, and not the synthetic treatment per se, is critical for optimizing the dosimetric properties of MgB4O7:Ce,Li. Specifically, we find that using nitrates of Mg, Li, and Ce as precursors enhances the luminescent intensity compared to preparations from their respective oxides. This can be attributed to a more efficient incorporation of Ce3+ into the MgB4O7 lattice, contrary to the case of oxide precursors, where segregation of CeO2 takes place. Our findings, alongside previous reports, pinpoint two pivotal factors in modulating the properties of MgB4O7:Ce,Li: sample preparation temperature and effective cerium concentration within the material.

The unveiling of superconductivity in La 3 Ni 2 O 7-δ under pressure, following the suppression of a high-temperature density wave (DW) state, has attracted considerable attention. Notably, the nature of this competing DW order remains elusive, presenting a crucial question that demands further investigation. Here, we employ the muon-spin rotation/relaxation ( μ SR) technique combined with dipole-field numerical analysis to probe the magnetic response of La 3 Ni 2 O 7-δ as a function of hydrostatic pressure. At ambient pressure, μ SR experiments reveal commensurate static magnetic order below T N ∼ 151K. The comparison of the observed internal magnetic fields with dipole-field calculations reveals the magnetic structure's compatibility with a stripe-type arrangement of Ni moments ( ∼ 0.3-0.7 μ B ), characterized by alternating lines of magnetic moments and non-magnetic stripes. Experiments under pressure (up to ∼ 2.3 GPa) demonstrate an increase of the magnetic ordering temperature at a rate d T N /dp ∼ 2.8 K/GPa. This trend is opposite in sign and significantly smaller in magnitude compared to the changes observed in the DW order of unknown origin reported by Wang et al. [arXiv:2309.17378]. Our findings reveal that the ground state of the La 3 Ni 2 O 7-δ system is characterized by the coexistence of two distinct orders — the spin density wave and, most likely, charge density wave — with a notable pressure-induced separation between them.

The discovery of pressure-induced superconductivity in two- and three-layer Ruddlesden-Popper nickelates has generated significant interest in these materials as a platform for unconventional superconductivity. While their ground state exhibits magnetism, a direct determination of their magnetic structure remains elusive. Understanding this aspect is crucial, as magnetism may play a role in the pairing mechanism of superconductivity in these compounds. We resolve the magnetic structures of the bilayer (2222) polymorphs of La3Ni2O7 and La2PrNi2O7 using neutron powder diffraction (NPD) and muon-spin rotation/relaxation (muSR). Magnetic neutron scattering appears below approximately 150 K in both compounds and is observed at the (qx, 1/2, 0) position, with qx = 0 and 1/2 for La3Ni2O7 and qx = 0 for La2PrNi2O7. Within a single layer, alternating low (0.05 - 0.075 muB) and high (0.66 muB) magnetic moment stripes form. These layers stack antiferromagnetically along the c-direction to form bilayers. The presence of two propagation vectors (qx = 0 and 1/2) in undoped La3Ni2O7 suggests the coexistence of two magnetic stacking polymorphs within a single crystallographic phase. The muSR spectra further confirm these magnetic structures. Our findings provide a detailed understanding of the magnetic ground state in bilayer nickelates, offering insights into possible precursor states that may influence the emergence of superconductivity in these materials.

Noncoplanar spin textures usually exhibit a finite scalar spin chirality (SSC) that can generate effective magnetic fields and lead to additional contributions to the Hall effect, namely topological or unconventional anomalous Hall effect (UAHE). Unlike topological spin textures (e.g., magnetic skyrmions), materials that exhibit fluctuation-driven SSC and UAHE are rare. So far, their realization has been limited to either low temperatures or high magnetic fields, both of which are unfavorable for practical applications. Identifying new materials that exhibit UAHE in a low magnetic field at room temperature is therefore essential. Here, we report the discovery of a large UAHE far above room temperature in epitaxial Fe3Ga4 films, where the fluctuation-driven SSC stems from the field-induced transverse-conical-spiral phase. Considering their epitaxial nature and the large UAHE stabilized at room temperature in a low magnetic field, Fe3Ga4 films represent an exciting, albeit rare, example of a promising material for spintronic devices.

Co3Sn2S2 has been reported to be a Weyl semimetal with c-axis ferromagnetism below a Curie temperature of 177 K. Despite the large interest in Co3Sn2S2, the magnetic structure is still unclear. Recent studies have challenged the magnetic phase diagram of Co3Sn2S2 by reporting unusual magnetic phases including the presence of exchange bias. Here we show, using X-ray Magnetic Circular Dichroism, a shift in the magnetization hysteresis loop, reminiscent of exchange bias and establish that the magnetic moment in Co arises from the spin, with negligible orbital moment. At 6 K, using spatially-resolved angle-resolved photoemission spectroscopy, we detect a butterfly-shaped electronic band structure at small regions of the sample distinct from the known ferromagnetic band structure. Our density functional theory calculations suggest that the butterfly bands correspond to an antiferromagnetic phase. Separately, we detect a sharp flat band at the Fermi level at some regions in the sample, which we attribute to a surface state. These different electronic states found in a stoichiometric intermetallic invite further efforts to explore the origin and nature of the electronic inhomogeneity associated to magnetism on the mesoscale. Co₃Sn₂S₂ has been reported to be a Weyl semimetal but its magnetic and electronic structure is still under debate. Here, X-ray magnetic circular dichroism reveals that cobalt magnetic moments originate from spin, rather than orbital moments, whereas spatially-resolved angle-resolved photoemission spectroscopy indicates the presence of electronic inhomogeneities in the band structure and magnetic phases.

Encoding information in antiferromagnetic (AFM) domains is a promising solution for the ever growing demand in magnetic storage capacity. The absence of a macroscopic magnetization avoids crosstalk between different domain states, enabling ultrahigh density spintronics1 while being detrimental to the domain detection and manipulation. Disentangling these merits and disadvantages seemed so far unattainable. We report evidence for a new AFM domain selection mechanism based on non-Zeeman susceptibility anisotropy induced by the relative orientation of external magnetic fields to the k-domains. Consequently, the charge transport response is controlled by the rotation of the magnetic field and a pronounced anisotropic magnetoresistance is found in the AFM phase of bulk materials Nd1−xCex CoIn5. Our results and the domain switching theory2 indicate that this constitutes a new effect which might be universal across multiband materials. It provides a novel mechanism to control and detect AFM domains opening new perspectives for AFM sprintronics.

The tetragonal 4 f -electron intermetallic ErB 4 is characterized by strong Ising anisotropy along the tetragonal c axis. The magnetic moments on the erbium sites can be mapped onto a Shastry-Sutherland lattice, resulting in geometrical frustration. At zero magnetic field ErB 4 exhibits collinear columnar antiferromagnetic (CAFM) order below T N = 15.4 K . In the presence of a magnetic field parallel to the c axis, ErB 4 exhibits a plateau at 1 / 2 of the saturation magnetization M S , which arises at a spin-flip transition at H 1 = 1.9 T. Fractional magnetization plateaus and other exotic spin phases are a well-established characteristic feature of frustrated spin systems. Monte Carlo simulations propose that ErB 4 is an ideal candidate to feature a spin supersolid phase in close vicinity of H 1 between the CAFM and M / M S = 1 / 2 plateau (HP) phase. Here, we combine single-crystal neutron diffraction and inelastic neutron scattering to study the magnetic phase diagram and the crystal electric-field (CEF) ground state of ErB 4 . Our measurements as a function of magnetic field find no signature of the spin supersolid phase but allow us to determine the magnetic structure of the HP phase to be of the up-up-up-down (uuud) type consistent with an Ising material. The magnetic moment μ CEF = 8.96 µ B expected from the CEF configuration determined by our inelastic neutron-scattering measurements is also consistent with the ordered moment observed in neutron diffraction, showing that the moments are fully ordered and close to the Er 3 + free ion moment (9.6 µ B ).

Recent band-structure calculations predicted that the ruthenium-based ternary silicides are three-dimensional Kramers nodal-line semimetals. Among them, NbRuSi and TaRuSi show bulk superconductivity (SC) below Tc similar to 3 K and 4 K, as well as spontaneous magnetic fields. The latter indicate the breaking of time-reversal symmetry and, thus, unconventional SC in both compounds. Previous temperature-dependent muon-spin spectroscopy studies failed to distinguish whether such compounds exhibit single-gap or multigap SC. Here we report on systematic measurements of the field-dependent muon-spin relaxation rates in the superconducting state and on temperature-dependent electrical resistivity and specific heat under applied magnetic fields. Both the upper critical field and the field-dependent superconducting relaxation are well described by a two-band model. By combining our experimental results with numerical band-structure calculations, we provide solid evidence for multiband SC in NbRuSi and TaRuSi, and thus offer further insight into the unconventional and topological nature of their superconductivity.

The elastic moduli provide unique insights into the thermodynamics of quantum materials, particularly into the symmetries broken at their phase transition. Here, we present a workflow to carve crystalline resonators via focused ion beam milling from small and oddly shaped crystals unsuitable for traditional measurements of elasticity. The accuracy of this technique is first established in silicon. Next, we showcase the capacity to probe changes in the electronic state with a resolution on the measured resonance frequency as small as 0.01% on YNiO3, a rare-earth perovskite nickelate, in which bulk single crystals have typical length scales of ≈40μm. Here, we observe a sharp 0.2% discontinuity in Young’s modulus of an YNiO3 cantilever at a magnetic phase transition. Finally, an additional potential of using free-standing cantilevers as a tool for examining the time-dependence of chemical changes is illustrated by laser-heating YNiO3.

The recent discovery of superconductivity in infinite layer thin films and bulk Ruddlesden-Popper nickelates has stimulated the investigation of other predicted properties of these materials. Among them, the existence of magnetism-driven ferroelectricity in the parent compounds RNiO3 (R = 4f lanthanide and Y) at the onset of the N & eacute;el order, T-N, has remained particularly elusive. Using diffraction techniques, we reveal here the existence of magnetostriction at T-N in bulk YNiO3 single crystals. Interestingly, the associated lattice anomalies are much more pronounced along the b crystal axis, which coincides with the electric polarization direction expected from symmetry arguments. This axis undergoes an abrupt contraction below T-N that reaches Delta b/b similar to -0.01%, a value comparable to those found in some magnetoresistive manganites and much larger than those reported for magnetism-driven multiferroics. This observation suggests a strong spin-lattice coupling in these materials, consistent with theoretical predictions. Using the symmetry-adapted distortion mode formalism, we identify the main ionic displacements contributing to the lattice anomalies and discuss the most likely polar displacements below T-N. Furthermore, our data support symmetric superexchange as the most likely mechanism responsible for the magnetoelastic coupling. These results, that may be common to the full RNiO3 family, provide new experimental evidence supporting the predicted existence of magnetism-driven ferroelectricity in RNiO3 perovskites.

Layered perovskites of general formula AA'CuFeO$_5$ are one of the few examples of cycloidal spiral magnets where the ordering temperatures $T_{spiral}$ can be tuned far beyond room temperature by introducing modest amounts of Cu/Fe chemical disorder in the crystal structure. This rare property makes these materials prominent candidates to host multiferroicity and magnetoelectric coupling at room temperature. Moreover, it has been proposed that the highest $T_{spiral}$ value that can be reached in this structural family ($\sim$ 400 K) corresponds to a paramagnetic-collinear-spiral triple point with potential to show exotic physics. Since generating high amounts of Cu/Fe disorder is experimentally difficult, the phase diagram region beyond the triple point has been barely explored. To fill this gap we investigate here the YBa$_{1-x}$Sr$_{x}$CuFeO$_{5}$ solid solutions ($0 \leq x \leq 1$), where we replace Ba with Sr with the aim of enhancing the impact of the experimentally available Cu/Fe disorder. Using a combination of bulk magnetization, synchrotron X-ray and neutron powder diffraction we show that the spiral state is destabilized beyond a critical degree of Cu/Fe disorder, being replaced by a non-frustrated, fully antiferromagnetic state with propagation vector k$_{c2}$ = $(\frac{1}{2}, \frac{1}{2}, 0)$ and ordering temperature $T_{coll2}$ $\geq$ $T_{spiral}$, which is progressively stabilized beyond the triple point. Interestingly, $T_{spiral}$ and $T_{coll2}$ increase with $x$ at the same rate. This suggests a common, disorder-driven origin, consistent with theoretical predictions.

Bipolaronic superconductivity is an exotic pairing mechanism proposed for materials like Ba_1-xK_xBiO_3 (BKBO); however, conclusive experimental evidence for a (bi)polaron metallic state in this material remains elusive. Here, we combine resonant inelastic x-ray and neutron total scattering techniques with advanced modelling to study the local lattice distortions, electronic structure, and electron-phonon coupling (e-ph) in BKBO as a function of doping. Data for the parent compound (x = 0) indicates that the electronic gap opens in predominantly oxygen-derived states strongly coupled to a long-range ordered breathing distortion of the oxygen sublattice. Upon doping, short-range breathing distortions and sizable (e-ph) coupling persist into the superconducting regime (x = 0.4). Comparisons with exact diagonalization and determinant quantum Monte Carlo calculations further support this conclusion. Our results provide compelling evidence that BKBO's metallic phase hosts a liquid of small (bi)polarons derived from local breathing distortions of the lattice, with implications for understanding the low-temperature superconducting instability

Abstract Charge density wave (CDW) orders in vanadium-based kagome metals have recently received tremendous attention, yet their origin remains a topic of debate. The discovery of ScV6Sn6, a bilayer kagome metal featuring an intriguing $$\sqrt{3}\times\sqrt{3}\times3$$ 3 × 3 × 3 CDW order, offers a novel platform to explore the underlying mechanism behind the unconventional CDW. Here, we combine high-resolution angle-resolved photoemission spectroscopy, Raman scattering and density functional theory to investigate the electronic structure and phonon modes of ScV6Sn6. We identify topologically nontrivial surface states and multiple van Hove singularities (VHSs) in the vicinity of the Fermi level, with one VHS aligning with the in-plane component of the CDW vector near the $$\bar{K}$$ K ¯ point. Additionally, Raman measurements indicate a strong electron-phonon coupling, as evidenced by a two-phonon mode and new emergent modes. Our findings highlight the fundamental role of lattice degrees of freedom in promoting the CDW in ScV6Sn6.

The REAl(Si,Ge) (RE = rare earth) family, known to break both the inversion- and time-reversal symmetries, represents one of the most suitable platforms for investigating the interplay between correlated-electron phenomena and topologically nontrivial bands. Here, we report on systematic magnetic, transport, and muon-spin rotation and relaxation (uSR) measurements on (Nd,Sm)AlGe single crystals, which exhibit antiferromagnetic (AFM) transitions at TN = 6.1 and 5.9 K, respectively. In addition, NdAlGe undergoes also an incommensurate-to-commensurate ferrimagnetic transition at 4.5 K. Weak transverse-field µSR measurements confirm the AFM transitions, featuring a ∼90