AV_3Sb_5 kagome metals are characterized by intertwined electronic and structural orders, which motivated extensive studies in recent years. Yet the details of the electronic state preceding the superconducting phase remain poorly understood. Here we extend our previous investigation [Phys. Rev. Research 7, L032046 (2025)] of RbV_3Sb_5 using avoided level crossing (ALC) muon-spin spectroscopy to the A = Cs and K systems. Consistent with our previous study, we identify a second transition whose origin cannot be attributed solely to an internal magnetic field, indicating the involvement of an additional electronic mechanism that subtly modifies the charge distribution within the V plane. In particular, the ALC results point towards an additional charge modulation taking place within the charge density wave (CDW) phase and occurring at T^*<T_CDW for A = Cs and Rb, or in the vicinity of T_CDW for A = K.

Broken time-reversal symmetry (BTRS) in superconductors is widely regarded as evidence for a multicomponent order parameter, yet the microscopic origin of the associated spontaneous magnetic fields remains unresolved. Sr 2 RuO 4 is a central example, where BTRS has been reported by several probes but its relation to superconductivity remains controversial. Here we use zero-field muon spin relaxation (μSR) to investigate how spontaneous magnetic fields evolve with pair-breaking disorder and crystal inhomogeneity in Sr 2 RuO 4 . We combine measurements on Sr 2−y La y RuO 4 single crystals at ambient pressure with measurements on stoichiometric Sr 2 RuO 4 under hydrostatic pressure, and compare these results with literature data spanning samples with different levels of inhomogeneity and Ru inclusions. We find that the superconductivity-induced enhancement of the exponential muon-spin relaxation rate, ∆Λ, associated with spontaneous magnetic fields decreases monotonically with La substitution and hydrostatic pressure, following approximately ∆Λ ∝ Tc2 when the effective density of field-generating inhomogeneities remains nearly unchanged. In contrast, ∆Λ is enhanced in samples containing stronger structural inhomogeneities, including nonmagnetic random disorder and Ru inclusions. These results support a picture in which spontaneous magnetic fields in Sr 2 RuO 4 are generated by nonmagnetic inhomogeneities within a BTRS superconducting state, with the strength controlled by the superconducting order parameter. More broadly, our findings provide an experimental framework for interpreting local magnetic signatures in multicomponent superconductors.

To achieve long-lasting, high-performance lithium-ion batteries, local inhomogeneity in current density must be avoided. One driver of such inhomogeneity is the spinodal decomposition of active materials into Li-rich and Li-poor phases during charge and discharge, respectively. Whether or not such phase separation occurs is linked to the dynamics of lithium (Li) at the active material surface and within its bulk. Here, we show that particle surface coatings can be designed to inhibit phase separation. Using LiFePO4 as a model system, we prepare particles with different coatings in order to tune Li dynamics and electronic structure and thereby induce or prevent phase separation, which we verify through experiment and ab initio calculations. We then leverage our findings to create a mixed ceramic-carbon coating that mitigates phase separation down to rates as low as 0.1C and simultaneously enables fast (dis)charge up to 5C.

The Muon station for sciEnce technoLOgy and inDustrY (MELODY) muon source is under construction at the China Spallation Neutron Source (CSNS). Its muon spin rotation/relaxation/resonance (mu SR) spectrometer detector system employs plastic scintillator arrays coupled with silicon photomultipliers (SiPMs). Studies on the performance of single-and multiple-channel detector modules will contribute to the design of the spectrometer. In this work, we investigated the signal amplitude of the single-channel module under different wrapped conditions using a 22Na radioactive source, and the signal amplitude linearity correlated with particle energy deposition tested in the proton beam terminal at CSNS. The mu SR experimental spectrum of the detector module composed of 24 channels was tested at the ISIS muon source under different magnetic fields. These results will provide important parameters and insights for the design and construction of the detector system for the first mu SR spectrometer at MELODY.

Layered kagome metals AV_{3}Sb_{5} provide a unique platform for studying the interplay between a variety of electronic orders, including superconductivity, charge density waves, nematic phases, and more. Understanding the evolution of the electronic state from the charge density wave to the superconducting transition is essential for unraveling the interplay of charge, spin, and lattice degrees of freedom giving rise to the unusual magnetic properties of these nonmagnetic metals. Previous zero-field and high-field muon spin relaxation (μSR) studies revealed two anomalies in the muon spin relaxation rate, a first change at T_{CDW}∼100K and a second steep increase at T^{*}∼40K, further enhanced by an applied magnetic field, thus suggesting a contribution of magnetic origin. In this Letter, we use the avoided level crossing μSR technique to investigate charge order in near-zero applied field. By tracking the temperature dependence of quadrupolar level-crossing resonances, we examined the evolution of the electric field gradient at V nuclei in the kagome plane. Our results show a significant rearrangement of the charge density starting at T^{*} indicating a transition in the charge distribution, likely electronic in origin, well below T_{CDW}. These findings, combined with previous μSR, scanning tunneling microscopy, and nuclear magnetic resonance (NMR) studies, emphasize the intertwined nature of proximate phases in these systems, with the charge rearrangement dominating the additional increase in μSR relaxation rate below T^{*}.

Muon Spin Rotation/Relaxation/Resonance (μSR) is a versatile and powerful non-destructive technology for investigating the magnetic properties of materials at the microscopic level. The μSR technique typically utilizes fully spin polarized beams of positive muons generated at particle accelerator facilities and measures the evolution of the muon spin polarization inside a sample to extract information about the local magnetic environment in materials. With the development of accelerator technologies, intensities of muon beams are being continuously improved, which will cause a pile-up problem to the μSR spectrometer. The first muon source in China, named MELODY, is currently under construction and will be a pulsed source of muons operated at a repetition frequency of only 1 Hz due to limitations of the accelerator system at CSNS. Consequently, there is a strong motivation to operate MELODY at significantly higher muon intensities. This necessitates an upgrade of the detector system inside the spectrometer, which should be smaller and faster to accommodate the increased intensity per pulse of muons. The Low Gain Avalanche Diode (LGAD), characterized by a typical pulse width of 2 ns and a segmentation size in the centimeters range, has the potential to significantly improve the counting rates of μSR spectrometers that utilize a high intensity pulsed muon source. Thus, it is expected that the LGAD detector is a promising candidate to enhance the performance of μSR spectrometers at the new MELODY muon source.To validate this, tests on the LGAD were conducted at the ISIS pulsed muon source at the Rutherford Appleton Laboratory, UK. This paper will describe the setup of the candidate LGAD devices and the subsequent analysis of the experiment data.

A spin-polarized muon implanted into a fluoride forms a coupled F–μ–F complex in which the muon spin and neighbouring fluorine nuclear spins become entangled. Here we apply radio-frequency (RF) excitation to this coupled system and use the three-dimensional distribution of emitted positrons to reconstruct the time-dependent evolution of the muon spin polarization. This three-dimensional readout, using single spin detection, is not possible in a single NMR experiment and demonstrates significant advantages that are achieved by using RF muon techniques. We demonstrate the application of this vector-readout method to the experimental observation of a muon spin echo signal that is controlled by the dipolar coupling to fluorine, as well as to a double resonance experiment, in which we use pulses tuned to separate frequencies to address both the muon and fluorine spins. This targeted approach, in which selective RF pulses can control the muon spin and other spins to which it is coupled, provides a novel route for probing systems of entangled spins.

Muon spin rotation/relaxation/resonance (μSR) spectroscopy uses highly polarized muons to study the microscopic magnetic structure and dynamics of condensed matter. In addition to the five existing muon facilities, the first Chinese muon source, the Muon station for sciEnce technoLOgy and inDustrY (MELODY), is planned to be constructed in Phase II of the China Spallation Neutron Source (CSNS). It aims to provide intense and pulsed muon beams to conduct μSR applications in multiple disciplines. The group from the University of Science and Technology of China (USTC) participated in the collaboration with the CSNS accelerator group for the construction of the muon source. The USTC group led the research and development (R&D) of the first-generation photomultiplier tube (PMT)-based μSR spectrometer, and the design of the second-generation silicon photomultiplier (SiPM)-based spectrometer. The PMT-based spectrometer is a 128-channel prototype to demonstrate and develop key detector and electronics technologies for the planned MELODY. After several iterative designs and updates of detectors and electronics, the spectrometer prototype achieved a 7-ns dead time, which can record more than 12 positrons per channel per pulse according to the ISIS running experience. Based on the technologies developed from the first-generation spectrometer, the second-generation spectrometer will use SiPMs to accommodate over 2500 detector units to make better use of muons in MELODY. The two generation developments of Chinese μSR spectrometers will greatly advance the construction of MELODY, and provide high-quality data for users to interpret material properties in the near future.

Abstract 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 (μ+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.

Advanced Physics ResearchVolume 3, Issue 3 2470008 Back CoverOpen Access Photophysical Ion Dynamics in Hybrid Perovskite MAPbX3 (X=Br, Cl) Single Crystals (Adv. Phys. Res. 3/2024) Konstantinos Papadopoulos, Konstantinos PapadopoulosSearch for more papers by this authorOla Kenji Forslund, Ola Kenji ForslundSearch for more papers by this authorStephen Cottrell, Stephen CottrellSearch for more papers by this authorKoji Yokoyama, Koji YokoyamaSearch for more papers by this authorPabitra K. Nayak, Pabitra K. NayakSearch for more papers by this authorFrancoise M. Amombo Noa, Francoise M. Amombo NoaSearch for more papers by this authorLars Öhrström, Lars ÖhrströmSearch for more papers by this authorElisabetta Nocerino, Elisabetta NocerinoSearch for more papers by this authorLars Börjesson, Lars BörjessonSearch for more papers by this authorJun Sugiyama, Jun SugiyamaSearch for more papers by this authorMartin Månsson, Martin MånssonSearch for more papers by this authorYasmine Sassa, Yasmine SassaSearch for more papers by this author Konstantinos Papadopoulos, Konstantinos PapadopoulosSearch for more papers by this authorOla Kenji Forslund, Ola Kenji ForslundSearch for more papers by this authorStephen Cottrell, Stephen CottrellSearch for more papers by this authorKoji Yokoyama, Koji YokoyamaSearch for more papers by this authorPabitra K. Nayak, Pabitra K. NayakSearch for more papers by this authorFrancoise M. Amombo Noa, Francoise M. Amombo NoaSearch for more papers by this authorLars Öhrström, Lars ÖhrströmSearch for more papers by this authorElisabetta Nocerino, Elisabetta NocerinoSearch for more papers by this authorLars Börjesson, Lars BörjessonSearch for more papers by this authorJun Sugiyama, Jun SugiyamaSearch for more papers by this authorMartin Månsson, Martin MånssonSearch for more papers by this authorYasmine Sassa, Yasmine SassaSearch for more papers by this author First published: 07 March 2024 https://doi.org/10.1002/apxr.202470008AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Graphical Abstract Photophysical Ion Dynamics In article number 2300120, Konstantinos Papadopoulos, Ola Kenji Forslund, Yasmine Sassa, and co-workers conduct a muon spin relaxation (μ+SR) study of hybrid perovskite MAPbX3 (X=Br, Cl) single crystals with and without illumination. The experimental and simulation results demonstrate an increase in organic molecule fluctuations under illumination, depending on the choice of the halide ion. These effects are correlated with the structural transformations and long carrier lifetimes observed in perovskite solar cells. Volume3, Issue3March 20242470008 RelatedInformation

We report on the magnetic behaviour of Nd5Ge3 by investigating through magnetization, neutron diffraction and muon spin relaxation measurements. Temperature dependent-magnetization, muon depolarization rate (λ), initial asymmetry (A0) and the stretched exponent (β) show a clear anomaly at the Néel temperature TN ∼ 54 K. However, the short-range correlated ferromagnetic interactions below TN are inferred from the diffuse scattering mechanism as revealed by zero-field neutron diffraction data. Narrow first order phase transition is due to the competing interaction of a high temperature weak-antiferromagnetic and low temperature glassy states. Magnetic field-induced reentrant spin glass state from a magnetic glass state is observed, before it transforms to a ferromagnetic state.

In this work we present a systematic set of measurements carried out by muon spin rotation/relaxation (mu+SR) and neutron powder diffraction (NPD) on the solid solution NaxCa1-xCr2O4. This study investigates Na-ion dynamics in the quasi-1D (Q1D) diffusion channels created by the honeycomb-like arrangement of CrO6 octahedra, in the presence of defects introduced by Ca substitution. With increasing Ca content, the size of the diffusion channels is enlarged; however, this effect does not enhance the Na ion mobility. Instead the overall diffusivity is hampered by the local defects and the Na hopping probability is lowered. The diffusion mechanism in NaxCa1-xCr2O4 is proposed to be interstitial and the activation energy as well as diffusion coefficient are determined for all the members of the solid solution.

Kagome superconductors AV$_{3}$Sb$_{5}$ provide a unique platform for studying the interplay between a variety of electronic orders, including superconductivity, charge density waves, nematic phases and more. Understanding the evolution of the electronic state from the charge density wave to the superconducting transition is essential for unraveling the interplay of charge, spin, and lattice degrees of freedom giving rise to the unusual magnetic properties of these nonmagnetic metals. Previous zero-field and high-field $\mu$SR studies revealed two anomalies in the muon spin relaxation rate, a first change at $T_{CDW} \sim 100$ K and a second steep increase at $T^{*}\sim 40$ K, further enhanced by an applied magnetic field, thus suggesting a contribution of magnetic origin. In this study, we use the avoided level crossing $\mu$SR technique to investigate charge order in near-zero applied field. By tracking the temperature dependence of quadrupolar level-crossing resonances, we examined the evolution of the electric field gradient at V nuclei in the kagome plane. Our results show a significant rearrangement of the charge density starting at $T^{*}$ indicating a transition in the charge distribution, likely electronic in origin, well below $T_{CDW}$. These findings, combined with previous $\mu$SR, STM, and NMR studies, emphasize the intertwined nature of proximate phases in these systems, with the charge rearrangement dominating the additional increase in $\mu$SR relaxation rate below $T^{*}$.

The number of methods to study transient paramagnetic hydrides at organometallic centres is extremely limited. The reactivity of {2Fe2S} centres with protons to produce both diamagnetic and paramagnetic systems is of central interest in developing novel catalysts for hydrogen production, inspired by the [FeFe]-hydrogenase enzymes. Here, we show how a combination of spectroscopic and electrochemical techniques is allowing access to detail of the reactivity of key species on these pathways. Electron paramagnetic resonance and infra-red spectroelectrochemical approaches have been used to observe the reduction of pre-generated diamagnetic hydrides. In contrast, avoided level crossing muon spin resonance (ALC-µSR) has been used to form the open-shell species directly and to examine the formation of short-lived intermediates in the reaction process. The combination of these techniques suggests the involvement of terminal hydrides or CO-protonation states on the pathway to the isolable bridging hydride products.

The next generation of muon spin spectrometers at the ISIS pulsed source are being developed to make efficient use of the increased source intensity. They will provide a transformational improvement in counting rates: ‘Super-MuSR’ will be the first of these instruments, capable of counting at ≈1 G·event·hr −1 . Key to delivering this capability is the development of highly pixelated, high density detector arrays that cover an appreciable solid angle, with each detector element optimised for counting at very high data rates. A series of ‘firsts’ are planned to optimise individual element count rate capability, where analogue waveforms recorded from SiPMs are fully digitised and processed using digital signal processing (DSP) methods at either software or firmware level. Full raw-signal digitisation will be achieved using the Xilinx Zynq ® UltraScale+ TM series of ‘system on a chip’ operating with ADCs capable of 1 GHz sampling, data handling using event streaming technology, and DSP to provide novel data correction techniques. We will discuss our concept and present preliminary results. Our prototype digitising data acquisition system, which is key to implementing a ‘digital data pipeline’ (DDP) is presented.

Abstract Strong quantum zero-point motion (ZPM) of light nuclei and other particles is a crucial aspect of many state-of-the-art quantum materials. However, it has only recently begun to be explored from an ab initio perspective, through several competing approximations. Here we develop a unified description of muon and light nucleus ZPM and establish the regimes of anharmonicity and positional quantum entanglement where different approximation schemes apply. Via density functional theory and path-integral molecular dynamics simulations we demonstrate that in solid nitrogen, α–N2, muon ZPM is both strongly anharmonic and many-body in character, with the muon forming an extended electric-dipole polaron around a central, quantum-entangled [N2–μ–N2]+ complex. By combining this quantitative description of quantum muon ZPM with precision muon quadrupolar level-crossing resonance experiments, we independently determine the static 14N nuclear quadrupolar coupling constant of pristine α–N2 to be –5.36(2) MHz, a significant improvement in accuracy over the previously-accepted value of –5.39(5) MHz, and a validation of our unified description of light-particle ZPM.

Online learning is being adopted across a wide range of disciplines, providing remote access to resources that serves to widen participation in training, and allowing courses to be created that are accessible to the diverse range of learning styles that have recently been identified. Online resources can also be used to supplement more traditional in-person training by bringing a cohort of learners up to a common minimum level beforehand, distributing materials during training, and reinforcing learning after the event. Over the last six years ISIS has developed a range of online learning materials about muon and neutron science, that can be used independently or in association with in-person training. Here we discuss the materials now available and how they were designed to work effectively, set out the opportunities and challenges of online training for facility users, and summarise planned future developments.

Molecular magnets are one of the key research themes of µ SR, but locating the muon stopping site in these compounds using density functional theory is often very challenging as their unit cells tend to contain a very large number of atoms. Nevertheless, many molecular magnets contain the [PF 6 ] − and [BF 4 ] − molecular ions, which, due to their fluorine nuclei, produce a distinctive µ SR spectrum, which can give information about the muon stopping site. This paper details the calculation of the muon sites in the much simpler materials KPF 6 and KBF 4 , providing insights which can be applied to situations where these molecular ions are found in complicated molecular magnets.

We have recently begun an investigation of paramagnetic (free-radical) final states formed on metal nanoparticles by muonium (Mu) reactivity with surface-adsorbed molecules. The nanoparticles are incorporated into mesoporous silica, facilitating specific reaction steps in the silica host that involve H-atom transfer reactions important to studies in heterogeneous catalysis. Radio frequency (RF) methods are an essential tool for characterising final state species in these systems, and a non-metallic sample cell is essential for the RF field to penetrate the sample. Unfortunately, several significant problems were encountered during initial experiments using a cell made from PEEK polymer, the most serious being a temporal instability in the signals likely due to reactant molecules adsorbing on the PEEK. This paper discusses the problems encountered using the PEEK cell, and then considers the development of a ceramic cell designed to give better reproducibility in the measurements. The success of this new cell is demonstrated both through off-line tests and by muon measurements, including a series of TF 2G Mu spin precession measurements verifying the temporal stability of the experimental setup. Finally, an RF cavity was fashioned, and RF measurements made for muons stopped in bare silica, with signals from both diamagnetic and paramagnetic muon states clearly seen.

Entangled spin states are created by implanting muons into single-crystal LiY_{0.95}Ho_{0.05}F_{4} to form a cluster of correlated, dipole-coupled local magnetic moments. The resulting states have well-defined energy levels allowing experimental manipulation of the state populations by electromagnetic excitation. Experimental control of the evolution of the muon spin polarization is demonstrated through application of continuous, radio-frequency electromagnetic excitation fields. A semiclassical model of quantum, dipole-coupled spins interacting with a classical, oscillating magnetic field accounts for the muon spin evolution. On application of the excitation field, this model shows how changes in the state populations lead to the experimentally observed effects, thus enabling a spectroscopic probe of entangled spin states with muons.