15th International Conference on Muon Spin Rotation, Relaxation and Resonance

For unambiguous interpretation of experimental µSR data, a thorough understanding of quantum zero-point motion (ZPM) of muons in materials is essential. Namely, while ZPM of light nuclei like hydrogen and lithium is known to play a pivotal role in the structure and dynamics of many important classes of materials$^{1,2}$, quantum effects of muons in solids can be even stronger due to the lower...

LF-$\mu$SR studies of spin diffusion started with mobile solitons [1] and polarons [2] in conducting polymers. Spin 1/2 antiferromagnetic chains can also support diffusive spin excitations in a certain parameter range of the XXZ model [3], showing either diffusive [4] or ballistic transport [5]. Recent LF-$\mu$SR studies of layered triangular lattice quantum spin liquid materials such as...

Our goal is to analyze the magnetic properties of the Kitaev material Na$_{2}$PrO$_{3}$ by comparing Neutron Scattering (NS) and Muon Spin Spectroscopy (μSR) experiments, with the addition of ab initio calculations.

Alkali-metal lanthanide oxides are an exciting field of study due to their frustrated geometry and possibly anisotropic magnetic interactions, as shown in Fig.1....

Low-dimensional magnetism continues to be of great theoretical and experimental interest, as reduced dimensionality supports strong fluctuations that can result in novel states and excitations. One theme in this field is the understanding of magnetism in reduced dimensions using notions from topology. Examples include topological objects such as walls, vortices and skyrmions, which can...

The rare-earth nickelates (RNiO$_3$) are a prototypical example of a metal-insulator transition. Among the RNiO$_3$, LaNiO$_3$ is unique in remaining metallic, although highly correlated. Interestingly, superlattices with insulating interlayers of LaAlO$_3$, can be driven insulating and antiferromagnetic if they are thin enough$^{1}$. We have used $^8$Li $\beta$-detected NMR ($\beta$-NMR), to...

The kagome lattice, the most prominent structural motif in quantum physics, benefits from inherent nontrivial geometry to host diverse quantum phases, ranging from spin-liquid phases, topological matter to intertwined orders, and most rarely unconventional superconductivity. Recently, charge sensitive probes have suggested that the kagome superconductors AV3Sb5 (A = K, Rb, Cs) [1] exhibit...

After two decades of research, the symmetry of the superconducting state in Sr$_2$RuO$_4$ is still under strong debate. The long time favoured spin-triplet px + i py state is ruled out by recent NMR experiments (1). However, in general time-reversal-symmetry breaking (TRSB) superconductivity indicates complex two-component order parameters. Probing Sr$_2$RuO$_4$ under uniaxial pressure offers...

The novel superconductor UTe$_2$ is a rare material wherein electrons form Cooper pairs in a unique spin-triplet state with potential topological properties. Theoretically, spin-triplet superconductivity in UTe$_2$ may be explained in terms of pairing mediated by either ferromagnetic or antiferromagnetic fluctuations, but experimentally the magnetic properties of UTe$_2$ remain enigmatic. Here...

Muonic X-ray Emission Spectroscopy (µXES) is a novel technique based on the detection of high-energy X-rays emitted after the interaction of a negative muon beam with matter. Thanks to the multi-elemental range, a negligible self-absorption effect of the x-rays and very low residual activity left in the sample after irradiation, the technique has been applied to a wide range of studies, with...

We have developed an elemental analysis technique with muonic x-ray on a Li-ion battery, taking advantages of muon and muonic x-rays, that is, accessibility of negative muons and high energy of muonic x-rays[1,2]. Especially, intense negative muon with low momentum at J-PARC enables us to investigate electrodes in Li-ion battery. There is no non-destructive method to observe Li directly deep...

Negative muon elemental analysis, which can measure elemental compositional distribution in the depth direction from 100 nm to several centimeters in a cm-order area with a depth resolution on the order of μm, is a revolutionary technology that enables nondestructive analysis of samples that previously could only be cut and analyzed in cross-section.　In recent years, this technique has begun...

The Muon-Induced X-ray Emission (MIXE) technique, first developed in the 1980's mostly for studying fundamental science, has recently seen a wide usage in the field of applied sciences, which includes archaeology, battery research, meteorites, ancient paintings etc.
Probing deep inside the material (up to a few mm) and being non-destructive, this technique is sensitive to all the elements of...

In the present work, we investigate the spin dynamics of one-dimensional spin-integer molecular nanomagnets ((CH$_3$)$_2$NH$_2$)V$_7$MF$_8$(O$_2$CtBu)$_ {162}$C$_7$H$_8$, with M=Ni/Mn, in short V$_7$M [1,2,3], by means of magnetization, susceptibility and MuSR measurements. These heterometallic nanomagnets contain seven vanadium ions (s=1) and one Ni$^{2+}$ (s=1) or Mn$^{2+}$ (s=5/2) ion,...

Typically, the solid state is not well suited to sustaining fast molecular motion - however, in recent years a variety of molecular machines, switches and rotors have been successfully engineered within porous crystals and on surfaces. Here, we report on a combined $^{1}$H-NMR [1] and $\mu$SR [2] study of fast-rotating molecular rotors within the bicyclopentane-dicarboxylate struts of a...

When positive muons (µ+) are implanted in insulating materials, they capture electrons to form muonium (Mu), a light isotope of H. This process makes muon spin resonance technique (µ SR) suitable for studying H interaction with matter, for example in hydrogen storage (HS) materials.
Among carbon-based materials, recently metal intercalated fullerides demonstrated to be promising for HS,...

The slow muons technique provides a quantitative approach to characterize the effect of various cover layers on the passivation of bulk defects near the p-n junction of solar cells [1].
Several cover layers on top of the chalcopyrite Cu(In,Ga)Se2 (CIGS) semiconductor absorber were investigated in this work, namely CdS, ZnSnO, Al2O3 and SiO2.

The figure shows the depth profile of a...

A positive muon spin rotation and relaxation ($\mu^{+}$SR) has been widely used for assorted materials to study a microscopic internal magnetic field. However, the counterpart technique, $\mu^{-}$SR, is less common mainly due to a small asymmetry of the $\mu^{-}$SR signal, typically 1/6 to that of $\mu^+$SR, caused by the loss of the spin polarization during a capture process of $\mu^-$ by...

Thin films of rare-earth metal oxyhydrides, such as yttrium oxyhydrides (YH$_{3-2x}$O$_x$), show a pronounced photochromic effect where the transparency of the films decreases reversibly over a large range of sub-bandgap wavelengths upon exposure to UV light. This makes these materials suitable candidates for applications in smart windows. However, the exact mechanism behind the photochromic...

While Li-ion batteries are considered the main candidate for mobile applications, compounds based on lithium’s heavier cousin, sodium (Na) have also started to receive a lot of attention lately as candidates for future batteries. One reason is that the Li-reserves are limited and if large scale energy storage become a reality in our future sustainable society, we might have to consider...

Spin polarized muons are widely known as an extremely sensitive local probe of magnetism. Additionally, positively charged muons implanted into semiconductors and insulators often bind an electron to form a charge-neutral muon-electron bound state frequently referred to as a muonium center. While studied extensively in non-magnetic semiconductors and insulators as light analogues of...

For several decades the intermetallic compound MnSi has fascinated the community for different aspects of its physical and magnetic properties. Among these properties is the exotic temperature-magnetic field phase diagram. While this diagram was first established in the 1970s, the exact nature of one of the phases was only identified in 2009 as a lattice of magnetic skyrmions, i.e. a...

The unitary evolution of a quantum system preserves its coherence, but interactions between the system and its environment result in decoherence, a process in which the quantum information stored in the system becomes degraded. A spin-polarized positively charged muon implanted in a fluoride crystal realizes such a coherent quantum system, and the entanglement of muon and nearest-neighbor...

Fe$_2$P alloys have been proposed as promising for applications in magnetocaloric refrigeration due to their first-order magnetic transitions coupled to a magnetoelastic transition, which gives rise to a giant magnetocaloric effect in the vicinity of their Curie temperature [1]. The magnetic structure of Fe$_2$P has been investigated and known to order ferromagnetically, with magnetic moments...

MuSpinSim is a Python software to simulate muon ($\mu$SR) experiments. In particular, it simulates the spin dynamics of a system of a muon plus other spins such as electrons and atomic nuclei. MuSpinSim can simulate various common experimental setups used in $\mu$SR, such as zero, transverse and longitudinal field experiments; and it can simulate $\mu$SR experiments that are resolved in time,...

Quantum coherence between an implanted positively-charged muon and nuclei in a solid was first conclusively demonstrated using muon-spin spectroscopy experiments on simple ionic fluorides [1]. In this case the nuclear spin $I=\frac 1 2$ of the $^{19}$F nuclei couples to the muon spin through the dipolar interaction.
Here we identify the first example of muon spin quantum coherence in systems...

Two of the most fundamental limitations of the muon-spin spectroscopy ($\mu^+$SR) technique are the lack of knowledge of the muon stopping site, and the uncertainty surrounding the degree to which the muon distorts its local environment. Over the past decade there has been significant progress in calculating muon stopping sites using ab initio methods, particularly density functional theory...

We present the results of muon spin relaxation ($\mu$SR) on the Ce-based quasikagome lattice CeRh$_{1-x}$Pd$_{x}$Sn ($x$ = 0.1 to 0.5). Our zero-field (ZF) $\mu$SR results reveal the absence of both static long-range magnetic order and spin freezing down to 0.05 K in the single crystal sample of $x = 0.1$. The weak temperature-dependent plateaus of the dynamic spin fluctuations below 0.2 K in...

The magnetic ground state of a quantum spin liquid (QSL) candidate compound, Lu$_2$Mo$_2$O$_{5-y}$N$_2$ oxynitride pyrochlore ($S=1/2$, Mo$^{5+}$), was investigated by muon spin rotation/relaxation experiment. In contrast to Lu$_2$Mo$_2$O$_7$ ($S=1$, Mo$^{4+}$) which exhibits a spin glass-like freezing of Mo moments below $T_g\simeq16$ K, no such spin freezing or long range magnetic order was...

The series of triangular compounds ACrO$_2$ is a model series for studying the Heisenberg model on S=3/2 (Cr$^{3+}$: half-filled t$_{2g}$ orbitals) triangular antiferromagnets and the impact of interlayer couplings on the dynamics. For this, we report µSR measurements on α-HCrO$_2$ and KCrO$_2$ [1] which complete former studies on the series of triangular compounds ACrO$_2$, A = Li , Na [2,...

The phrase ‘quantum spin liquid’ (QSL) refers to a system in which strong quantum fluctuations prevent long-range magnetic order from being established, even at temperatures well below any interaction energy scale. No spontaneous symmetry breaking is involved, nor a conventional local order parameter. Thus, it is not described using the Landau theory of phase transitions and constitutes a...

A new method to measure the superconducting stiffness tensor ${\bar \rho _s}$, without subjecting the sample to magnetic field, is applied to La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) [1]. The method is based on the London equation $\mathbf{ J } = - \bar{{ \rho}}_\mathbf{s}\mathbf{ A}$, where $\mathbf{ J}$ is the current density and $\mathbf{ A}$ is the vector potential. Using rotor free $\mathbf{...

The Pd-Bi family of compounds has become quite popular system to explore topological superconductivity due to their intrinsic capability to maintain strong spin orbit coupling (SOC). Amongst various members of this family, $\alpha$-PdBi$_2$ turns out to be very promising due to its superconducting ($T_c$ = 1.7 K) as well as topological properties such as Dirac point at 1.26 eV below the Fermi...

The iron-chalcogenide FeSe exhibits various electronic states such as superconductivity, the so-called electronic nematicity, as well as a magnetic order under hydrostatic pressure. Therefore, this system attracts considerable research attention in an effort to understand the interplay between the different electronic states. In S-substituted thin films of FeSe$_{1-x}$S$_x$ in which positive...

Recent family of Kagome superconductors AV3Sb5 (A = Rb, K, Cs) offers a natural playground to study the interplay between different electronic states such as non-trivial chiral charge order (CO) and unconventional superconductivity [1-5]. This is because of its unique crystal structure that results in flat bands across the Brillouin zone, crossing of linear bands at K-corner, appearance of van...

Spontaneous rotational-symmetry breaking (RSB) in the amplitude of the superconducting gap is a necessary condition for “nematic” superconductivity. This was evidenced in the topological superconductor Cu$_x$Bi$_2$Se$_3$ where, despite the threefold symmetry of its lattice, a twofold symmetry of electronic properties emerged from nuclear magnetic resonance$^1$, transport$^2$, and...

The model describes the reaction of atom-like muonium with the host lattice at the end of the implantation trajectory. Reactions of the bare muon with the host or prompt formation of the final states are not covered by this model. Since these alternative processes are temperature independent, their maximum contribution can be estimated from the smallest value that occurs at any given...

The usual response of muonium to an external magnetic field is dominated by the hyperfine interaction, which causes the observed spectrum to show the transition frequencies between different muonium spin states. However, we have recently discovered an unconventional magnetic muonium state in 2H-MoTe$_2$ where the muonium acts a magnetic impurity, which polarizes the local electronic magnetic...

Hydrogen passivation of defects is commonly used to reduce defects in semiconductors such as GaAs, diamond, and Si. We recently found by experiment that atomic hydrogen is also very effective in significantly increasing a minority-carrier lifetime (> 10 μs) in BaSi2, one of the emerging materials for thin-film solar cell applications. This means that defects no longer act as recombination...

Photoexcited muon spin spectroscopy (photo-$\mu$SR) was used to measure excess charge carrier lifetimes in passivated silicon wafers. Optically generated excess carriers interact with muonium centres via carrier exchange interaction and induce relaxation in the $\mu$SR time spectrum. The photo-$\mu$SR technique utilises this additional relaxation rate as a measure of the excess carrier...

The study on the electronic state of muon as pseudo-hydrogen (represented by the elemental symbol Mu) by muon spin rotation has long been appreciated as one of the few methods to experimentally access the electronic state of dilute hydrogen (H) in semiconductors and dielectrics. Meanwhile, theoretical predictions on the electronic state of H in these materials by first-principles calculations...

Metal halide perovskites (MHPs) have attracted great attention in recent years due to their enormous potential for application in optoelectronic devices. However, the defects at surface/interfaces and grain boundaries of perovskite films, which impede the further enhancement of power conversion efficiency (PCE) and long-term stability of halide perovskite solar cells (PSCs), still need to be...

We demonstrate the most fundamental coherent control techniques by excitation of microwave spin transitions in muonium, namely driven Rabi oscillations and Ramsey fringes upon free evolution. Unprecedented performance is achieved by triggering microwave pulses by a single implanted muon, which enables coherent spin manipulation of individual muonium atoms.

As a first example, we suppress...

We recently proposed new precision microwave spectroscopy measurements of the ground-state hyperfine structure (HFS) of muonic helium atom [1]. Muonic helium is a hydrogen-like atom composed of a helium atom with one of its electrons replaced by a negative muon. The ground-state HFS, resulting from the interaction of the remaining electron and the negative muon magnetic moment, is very similar...

Over the past decade, we have been using beta-detected NMR to examine the properties of amorphous materials. While this has typically focused on polymers,$^1$ we have recently been interested in ionic liquids (ILs). ILs are binary mixtures: they are composed of two oppositely charged molecular species. They are also liquid at room temperature. Their properties, determined by strong...

In the drive to replace fossil fuels with sustainable alternatives, achieving the reversible interconversion of protons and dihydrogen is a crucial target. The reaction can be carried out readily using platinum-based systems, but the cost and availability of this precious metal preclude scaling such approaches. In nature, the [FeFe]-hydrogenase enzymes have evolved to perform the very same...

Since the implementation of $\beta$-detected NMR ($\beta$-NMR) at TRIUMF, it has mainly been used to study condensed matter systems ranging from metals to superconductors to topological insulators. In the last few years, there has been a desire to extend the applications of $\beta$-NMR to include the study of biochemical problems. For a number of metal ions in our body, such as Mg(II),...

Over the past four decades, muon spin rotation and relaxation technique in water and ice has been reported by several groups [1-4]. Most of the previous studies were focused on muonium chemistry (detection, its relaxation, reaction and frequencies) in water and ice. To deepen the understanding of muon behavior in water and application of $\mu$SR to life sciences and hydrated samples, we...

Layered transition-metal dichalcogenides (TMDs) are proposed as building blocks for van der Waals (vdW) heterostructures. Semiconducting TMDs are further prone to host magnetic impurities, e.g. at defects or interstitials. Here we investigate the behavior of interstitial $^8$Li$^+$ implanted into 2H-MoTe$_2$ at depths of $\sim$110 nm with $\beta$-detected NMR. We find that unlike muons...

Magnetic topological phases of quantum matter are an emerging frontier in physics and material science [1-6], of which kagome magnets appear as a highly promising platform. Here, we explore magnetic correlations in the recently identified topological kagome system TbMn$_{6}$Sn$_{6}$ using $\mu$SR, combined with local field analysis and neutron diffraction [1,4]. Our studies identify an...

A test of the abstract system

The fineness and quality of a state’s coinage is often used as a proxy for its fiscal health, meaning the purity and chemical composition of coins are of real historical interest. Sampling of such objects is often at the surface or near-surface, but, in ancient coinages, these areas can be unrepresentative of the bulk alloy – sometimes radically so. In this paper, investigations on Roman gold...