Low-dimensional quantum magnets are a versatile materials platform for studying the emergent many-body physics and collective excitations that can arise even in systems with only short-range interactions. Understanding their low-temperature structure and spin Hamiltonian is key to explaining their magnetic properties, including unconventional quantum phases, phase transitions, and excited states. We study the metal-organic coordination compound (C5H9NH3)2CuBr4 and its deuterated counterpart, which upon its discovery was identified as a candidate two-leg quantum (S=12) spin ladder in the strong-leg coupling regime. By growing large single crystals and probing them with both bulk and microscopic techniques, we deduce that two previously unknown structural phase transitions take place between 136 and 113 K. The low-temperature structure has a monoclinic unit cell that gives rise to two inequivalent spin ladders. We further confirm the absence of long-range magnetic order down to 30 mK and investigate the implications of this two-ladder structure for the magnetic properties of (C5H9NH3)2CuBr4 by analyzing our own specific-heat and susceptibility data.

In this study, we investigate the influence of Cr-Cr distances on the magnetic properties of triangular lattice antiferromagnets through the lens of the recently synthesized Cr compounds LiCrSe2, 2 , LiCrTe2, 2 , and NaCrTe2. 2 . Our comprehensive analysis integrates existing magnetic structure data and new insights from muon spin rotation measurements, revealing a striking mutual influence between strongly correlated electrons and structural degrees of freedom in systems possessing very different magnetic properties despite having the same crystal symmetry. In particular, we delineate how Cr-Cr distances specifically dictate the magnetic behaviors of the triangular lattice antiferromagnets LiCrSe2, 2 , LiCrTe2, 2 , and NaCrTe2. 2 . By crafting phase diagrams based on these distances, we establish a clear correlation between the structural parameters and the magnetic ground states of these materials together with a wide variety of trivalent Cr triangular lattice layered magnets. Our analysis uncovers a transition range for in-plane and out-of-plane Cr-Cr distances that demarcates distinct magnetic behaviors, highlighting the nuanced role of lattice geometry in the spin-lattice interaction and electron correlation dynamics.

Understanding the processes guiding the confinement of adsorbed H2 in different porous structures is vital for the development of adsorbents for effective cryo-adsorptive H2 storage systems. Quasi-elastic neutron scattering (QENS) is applied over a wide range of timescales (0.2 ps – 150 ps) to determine different self-diffusion mechanisms of H2 adsorbed in a carbide (synthesized from TiC via the sol-gel method) derived carbon (sol-gel TiC-CDC) adsorbent with hierarchical porous structure. The bulk and porous structure is characterized by gas adsorption, Raman spectroscopy, and wide-angle X-ray scattering methods. Sol-gel TiC-CDC belongs to a series of CDCs that have been previously characterized and where the self-diffusion of adsorbed H2 has been investigated with QENS. Sol-gel TiC-CDC is very mesoporous, has relatively high stacking (2.76 graphenic layers per stack), and small interlayer spacing of graphenic sheets (3.43 Å) in comparison to other CDCs in the series, thus, being a well-ordered highly porous CDC. Restricted rotational self-diffusion of adsorbed H2 is determined in ultramicropores (pore width, w, < 7 Å) and translationally self-diffusing H2 adsorbed in multilayers across multiple timescales are determined in micro- and mesopores (7 Å < w < 500 Å). The microporous and graphenic structure of the CDC does not remarkably affect the self-diffusion of H2 at high surface coverages. The simultaneous determination of adsorbed H2 motions across different timescales allows to analyze the influence of micro- and mesopores under H2 loading conditions, which are close to the ones used in technical applications and are vital for adsorbent optimization.

Virucidal filter materials were prepared by electrospinning a solution of 28 wt % poly(vinylidene difluoride) in N,N-dimethylacetamide without and with the addition of 0.25 wt %, 0.75 wt %, 2.0 wt %, or 3.5 wt % Cu(NO3)2 · 2.5H2O as virucidal agent. The fabricated materials had a uniform and defect free fibrous structure and even distribution of copper nanoclusters. X-ray diffraction analysis showed that during the electrospinning process, Cu(NO3)2 · 2.5H2O changed into Cu2(NO3)(OH)3. Electrospun filter materials obtained by electrospinning were essentially macroporous. Smaller pores of copper nanoclusters containing materials resulted in higher particle filtration than those without copper nanoclusters. Electrospun filter material fabricated with the addition of 2.0 wt % and 3.5 wt % of Cu(NO3)2 · 2.5H2O in a spinning solution showed significant virucidal activity, and there was 2.5 ± 0.35 and 3.2 ± 0.30 logarithmic reduction in the concentration of infectious SARS-CoV-2 within 12 h, respectively. The electrospun filter materials were stable as they retained virucidal activity for three months.

The present study investigated the magnetic nature of a solid solution system consisting of EuCo2P2 and CaCo2P2 using a muon spin rotation and relaxation (mu +SR) technique, which is sensitive to local magnetic environments. The former compound EuCo2P2 is known to enter an incommensurate helical antiferromagnetic (AF) phase below 66 K with neutrons, which was confirmed by the present mu +SR. The magnitude of the ordered Eu moments proposed with neutrons was found to be consistent with that estimated by mu +SR. Furthermore, the latter lattice-collapsed tetragonal phase compound CaCo2P2 is known to enter an A-type AF phase below 90 K, and mu +SR measurements on single crystals revealed the presence of a spin reorientation transition at around 40 K, below which the A-type AF order is likely to be completed. Although all Eu1-xCaxCo2P2 compounds were found to enter a magnetic phase at low temperatures regardless of x, a static ordered state was formed only at the vicinity of the two end compounds, i.e., 0 x 0.4 and 0.9 x 1. Instead, a disordered state, i.e., a random spin-glass state, short-range ordered state, or highly fluctuating state was found in the x range between 0.4 and 0.9, even at the lowest measured temperature (2 K). Together with the magnetization data, our findings clarified the magnetic phase diagram of Eu1-xCaxCo2P2, where a ferromagnetic exchange interaction between Co ions through the Eu2+ ion competes with a direct AF interaction among the Co ions, particularly in the x range between 0.57 and 0.9. This competition yielded multiple phases in Eu1-xCaxCo2P2.

Hybrid organic-inorganic perovskites (HOIPs) are promising candidates for next-generation photovoltaic materials. However, there is a debate regarding the impact of interactions between the organic center and the surrounding inorganic cage on the solar cell's high diffusion lengths. It remains unclear whether the diffusion mechanism is consistent across various halide perovskite families and how light illumination affects carrier lifetimes. The focus is on ion kinetics of (CH3NH3)PbX3 (X = Br, Cl) perovskite halide single crystals. Muon spectroscopy (mu+SR)is employed to investigate the fluctuations and diffusion of ions via the relaxation of muon spins in local nuclear field environments. Within a temperature range of 30-340 K, ion kinetics are studied with and without white-light illumination. The results show a temperature shift of the tetragonal-orthorhombic phase transition on the illuminated samples, as an effect of increased organic molecule fluctuations. This relation is supported by density functional theory (DFT) calculations along the reduction of the nuclear field distribution width between the phase transitions. The analysis shows that, depending on the halide ion, the motional narrowing from H and N nuclear moments represents the molecular fluctuations. The results demonstrate the importance of the halide ion and the effect of illumination on the compound's structural stability and electronic properties.

The electron-phonon interaction is in many ways a solid state equivalent of quantum electrodynamics. Being always present, the e-p coupling is responsible for the intrinsic resistance of metals at finite temperatures, making it one of the most fundamental interactions present in solids. In typical metals, different regimes of e-p scattering are separated by a characteristic phonon energy scale - the Debye temperature. However, in metals harboring very small Fermi surfaces a new scale emerges - the Bloch-Grüneisen temperature. This is a temperature at which the average phonon momentum becomes comparable to the Fermi momentum of the electrons. Here we report sub-Kelvin transport and sound propagation experiments on the Dirac semimetal ZrTe₅. The combination of the simple band structure with only a single small Fermi surface sheet allowed us to directly observe the Bloch-Grüneisen temperature and its consequences on electronic transport of a 3D metal in the limit where the small size of the Fermi surface leads to effective restoration of translational invariance of free space. Our results indicate that on entering this hydrodynamic transport regime, the viscosity of the Dirac electronic liquid undergoes an anomalous increase beyond the theoretically predicted T⁵ temperature dependence. Extension of our measurements to strong magnetic fields reveal that, despite the dimensional reduction of the electronic band structure, the electronic liquid retains characteristics of the zero-field hydrodynamic regime up to the quantum limit. This is vividly reflected by an anomalous suppression of the amplitude of quantum oscillations seen in the Shubnikov-de Haas effect.

Strongly correlated electron materials are often characterized by competition and interplay of multiple quantum states. For example, in high-temperature cuprate superconductors unconventional superconductivity, spin- and charge-density wave orders coexist. A key question is whether competing states coexist on the atomic scale or if they segregate into distinct regions. Using X-ray diffraction, we investigate the competition between charge order and superconductivity in the archetypal cuprate La2−xBaxCuO4, around x = 1/8-doping, where uniaxial stress restores optimal 3D superconductivity at σ3D ≈ 0.06 GPa. We find that the charge order peaks and the correlation length along the stripe are strongly reduced up to σ3D. Upon the increase of stress beyond this point, no further changes were observed. Simultaneously, the charge order onset temperature only shows a modest decrease. Our findings suggest that optimal 3D superconductivity is not linked to the absence of charge stripes but instead requires their arrangement into smaller regions. Our results provide insight into the length scales over which the interplay between superconductivity and charge order takes place.

In this work, we propose hydroxyapatite (HA) as a hard template to unlock the porosity of Fe-N-C catalyst materials. Using HA, a naturally occurring mineral that can be removed with nitric acid, in the synthesis generates a catalyst material with a unique porous network comprising abundant pores and interparticle cavities ranging from 10 to 3000 nm. Hard templating with HA alongside ZnCl2 as a micropore former results in a Fe-N-C catalyst based on naturally abundant peat with excellent oxygen reduction activity in alkaline conditions. A half -wave potential of 0.87 V vs RHE and a peak power density of 1.06 W cm-2 were achieved in rotating ring disk electrode and anion exchange membrane fuel cell experiments, respectively, rivaling the performance of other state-of-the-art platinum-free catalysts presented in the literature. A combined approach of using renewable peat as a carbon source and HA as a hard template offers an environmentally friendly approach to high-performance Fe-N-C catalysts with abundant porosity.

We investigated the electronic structure of the antiferromagnetic Kondo lattice CePd5Al2 using high-resolution angle-resolved photoemission spectroscopy. The experimentally determined band structure of the conduction electrons is predominated by the Pd 4d character. It contains multiple hole and electron Fermi pockets, in good agreement with density functional theory calculations. The Fermi surface is folded over Q0=(0,0,1), manifested by Fermi surface reconstruction and band folding. Our results suggest that Fermi surface nesting drives the formation of antiferromagnetic order in CePd5Al2.