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Quantum spin liquid (QSL) is a disordered state of quantum-mechanically entangled spins commonly arising from frustrated magnetic dipolar interactions. However, QSL in some pyrochlore magnets can also come from frustrated magnetic octupolar interactions. Although the key signature for both dipolar and octupolar interaction-driven QSL is the presence of a spin excitation continuum (spinons) arising from the spin quantum number fractionalization, an external magnetic field-induced ferromagnetic order will transform the spinons into conventional spin waves in a dipolar QSL. By contrast, in an octupole QSL, the spin waves carry octupole moments that do not couple, in the leading order, to the external magnetic field or to neutron moments but will contribute to the field dependence of the heat capacity. Here we use neutron scattering to show that the application of a large external magnetic field to Ce2Zr2O7, an octupolar QSL candidate, induces an Anderson-Higgs transition by condensing the spinons into a static ferromagnetic ordered state with octupolar spin waves invisible to neutrons but contributing to the heat capacity. Our theoretical calculations also provide a microscopic, qualitative understanding for the presence of octupole scattering at large wavevectors in Ce2Sn2O7 pyrochlore, and its absence in Ce2Zr2O7. Therefore, our results identify Ce2Zr2O7 as a strong candidate for an octupolar U (1) QSL, establishing that frustrated magnetic octupolar interactions are responsible for QSL properties in Ce-based pyrochlore magnets.

Glassy magnetic behavior has been observed in a wide range of crystalline magnetic materials called spin glass. Here, we report spin glass behavior in a structural glass of a magnetic ionic liquid, C4mimFeCl4. Magnetization measurements demonstrate that an antiferromagnetic ordering occurs at TN = 2.3 K in the crystalline state, while a spin glass transition occurs at TSG = 0.4 K in the structural glass state. In addition, localized magnetic excitations were found in the spin glass state by inelastic neutron scattering, in contrast to spin-wave excitations in the ordered phase of the crystalline sample. The localized excitation was scaled by the Bose population factor below TSG and gradually disappeared above TSG. This feature is highly reminiscent of boson peaks commonly observed in structural glasses. We suggest the “magnetic” boson peak to be one of the inherent dynamics of a spin glass state.

Observation of a quantum spin liquid (QSL) state is one of the most important goals in condensed-matter physics, as well as the development of new spintronic devices that support next-generation industries. The QSL in two dimensional quantum spin systems is expected to be due to geometrical magnetic frustration, and thus a kagome-based lattice is the most probable playground for QSL. Here, we report the first experimental results of the QSL state on a square-kagome quantum antiferromagnet, KCu6AlBiO4(SO4)5Cl. Comprehensive experimental studies via magnetic susceptibility, magnetisation, heat capacity, muon spin relaxation (μSR), and inelastic neutron scattering (INS) measurements reveal the formation of a gapless QSL at very low temperatures close to the ground state. The QSL behavior cannot be explained fully by a frustrated Heisenberg model with nearest-neighbor exchange interactions, providing a theoretical challenge to unveil the nature of the QSL state., There exist many theoretical models of frustrated quantum magnetism, most of which lack convincing experimental realisations. Here the authors combine several experimental methods to argue that KCu6AlBiO4(SO4)5Cl behaves as a square-kagome-lattice quantum Heisenberg antiferromagnet.

International audience; Using a minimal model approach for interpreting the intermediate scattering function, F(Q, t), to analyze quasi-elastic neutron scattering (QENS) data from interlayer water as a function of temperature in the 2D-layered clay minerals montmorillonite (Mt) and hectorite (Ht) a clear difference in behavior was observed. This was related to the polarization effect induced on the water molecules by both the exchangeable cation and surface charge within the interlayer. Although crucial for improving the wide range of industrial applications of clays as well as for explaining water uptake and retention by clays such information is neither obtained straightforwardly by other experimental methods nor fully accounted by molecular dynamics simulations. Furthermore, analysis of the evolution of the fitted parameters as a function of temperature shows that hydrogen atoms have a relaxation with a smaller average motional amplitude for Mt. Physically this can be explained as stronger hydrogen-bonding by water at the interlayer surfaces in Mt. These results allow for a novel and realistic description of these nanomaterials at the atomic scale, which is crucial for improving functional properties. These findings also prove that this new approach to modeling QENS captures subtle changes hidden in the spectra.

Details of the background, that is, “unwanted signals accumulated by the data acquisition system of neutron instruments,” observed by the cold-neutron chopper spectrometer AMATERAS installed at the Materials and Life Science Experimental Facility at J-PARC are reported. In the design phase of AMATERAS, we carefully considered the achievement of high signal-to-noise ratio, and possible countermeasures were implemented. Actually, recent scientific outputs from AMATERAS indicates that the spectrometer is one of excellent neutron instruments with low background. In spite of that, in nine years of AMATERAS operation, we have encountered unwanted signals due to various reasons, including γ rays emitted at materials on or near the beam line including the sample itself, scattered neutrons from the beam line devices, air scattering, electronic noise in data acquisition system, cosmic rays, T0 burst, and other unknown sources. In this report, we discuss the background observed by AMATERAS, especially in the conditions of without samples, comprehensively. The possible sources of these signals and the countermeasures considered against the above sources are discussed, which may be helpful to those who are engaged in other existing or planned neutron-scattering instruments.

Seven time-of-flight quasielastic/inelastic neutron scattering instruments are installed on six beamlines in the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC). Four of these instruments are chopper-type direct-geometry spectrometers, one is a near-backscattering indirect-geometry spectrometer, and the other two are spin-echo-type spectrometers. This paper reviews the characteristic features, recent scientific outcomes, and progress in development of MLF spectrometers.

Magnets are important for studying magnetism and are commonly used as sample environment devices of neutron scattering instruments. However, the use of magnets was prevented at the time-of-flight direct-geometry neutron spectrometer 4SEASONS in Materials and Life Science Experimental Facility (MLF) at J-PARC, because the instrument is surrounded by iron components, and it is equipped with a piece of equipment operated with magnetic bearings. In the present work, we investigate the influence of stray magnetic fields from a superconducting magnet which is shared among neutron scattering instruments in MLF. Based on the investigation, we modified 4SEASONS such that it can be used with the magnet. Finally, we successfully performed the first inelastic neutron scattering experiments with applied magnetic fields using this sample environment.

Crystal and magnetic structures of the mineral centennialite ${\mathrm{CaCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Cl}}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}0.6{\mathrm{H}}_{2}\mathrm{O}$ are investigated by means of synchrotron x-ray diffraction and neutron diffraction measurements complemented by density functional theory (DFT) and pseudofermion functional renormalization group (PFFRG) calculations. ${\mathrm{CaCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Cl}}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}0.6{\mathrm{H}}_{2}\mathrm{O}$ crystallizes in the $P\overline{3}m1$ space group and ${\mathrm{Cu}}^{2+}$ ions form a geometrically perfect kagome network with antiferromagnetic ${J}_{1}$. No intersite disorder between ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Ca}}^{2+}$ ions is detected. ${\mathrm{CaCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Cl}}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}0.6{\mathrm{H}}_{2}\mathrm{O}$ enters a magnetic long-range ordered state below ${T}_{\text{N}}=7.2$ K, and the $\mathbf{q}=\mathbf{0}$ magnetic structure with negative vector spin chirality is obtained. The ordered moment at 0.3 K is suppressed to $0.58(2){\ensuremath{\mu}}_{\text{B}}$. Our DFT calculations indicate the presence of antiferromagnetic ${J}_{2}$ and ferromagnetic ${J}_{d}$ superexchange couplings of a strength which places the system at the crossroads of three magnetic orders (at the classical level) and a spin-$\frac{1}{2}$ PFFRG analysis shows a dominance of $\mathbf{q}=\mathbf{0}$ type magnetic correlations, consistent with and indicating proximity to the observed $\mathbf{q}=\mathbf{0}$ spin structure. The results suggest that this material is located close to a quantum critical point and is a good realization of a ${J}_{1}\ensuremath{-}{J}_{2}\ensuremath{-}{J}_{d}$ kagome antiferromagnet.

$\mathrm{NaYb}{\mathrm{O}}_{2}$ has been reported as a possible host for the quantum spin-liquid state. Here, the composition-dependent polycrystalline $\mathrm{N}{\mathrm{a}}_{1\text{\ensuremath{-}}x}\mathrm{Yb}{\mathrm{O}}_{2}$ ($x=0$, 0.03, and 0.07) has been investigated by combining high-field magnetizations and inelastic neutron scattering techniques. For the $x=0$ sample, no signature of a magnetic order is observed down to 0.3 K. Inelastic neutron scattering measurement suggests a continuous low-energy excitation spectrum centered at momentum transfer $(Q)\ensuremath{\sim}1.25\phantom{\rule{0.16em}{0ex}}{\AA{}}^{\ensuremath{-}1}$ and extending up to energy transfer ($E$) \ensuremath{\sim} 2.0 meV. In contrast, $x=0.03$ and 0.07 samples exhibit magnetic transitions at 1.1 and 2.3 K, respectively. High-field magnetization measurements indicate similar behaviors for $x=0$ and 0.03 samples including plateaulike features at the 1/3 saturated magnetization, which implies that the spin disorder in the $x=0$ sample might be suppressed preceding the emergence of the up-up-down phase. This composition- and field-dependent study allows us to construct complete phase diagrams indicating that $\mathrm{NaYb}{\mathrm{O}}_{2}$ is a promising candidate for the quantum spin-liquid state in close proximity to the antiferromagnetic instability tuned by the application of magnetic fields as well as controlling the concentration of $\mathrm{N}{\mathrm{a}}^{+}$ ion vacancies.

Hydration water dynamics were measured by quasi-elastic neutron scattering with H2O/D2O contrast for two DNA dodecamers, 5’CGCGAATTCGCG’3 and 5’CGCGTTAACGCG’3, which have been computationally shown to be structurally rigid and flexible, respectively. The dynamical transitions of the hydration water as well as DNA were observed for both sequences at approximately 240 K. Above the transition temperature, the mean square displacements of the hydration water for the rigid sequence were smaller than those for the flexible one. Furthermore, the relaxation time of the hydration water was longer in the rigid DNA than in the flexible DNA. We suggest that hydration water dynamics on the picosecond timescale are associated with sequence-dependent deformability of DNA.

The dimerized quantum magnet ${\mathrm{BaCuSi}}_{2}{\mathrm{O}}_{6}$ was proposed as an example of ``dimensional reduction'' arising near the magnetic-field-induced quantum critical point (QCP) due to perfect geometrical frustration of its interbilayer interactions. We demonstrate by high-resolution neutron spectroscopy experiments that the effective intrabilayer interactions are ferromagnetic, thereby excluding frustration. We explain the apparent dimensional reduction by establishing the presence of three magnetically inequivalent bilayers, with ratios $3\ensuremath{\mathbin:}2\ensuremath{\mathbin:}1$, whose differing interaction parameters create an extra field-temperature scaling regime near the QCP with a nontrivial but nonuniversal exponent. We demonstrate by detailed quantum Monte Carlo simulations that the magnetic interaction parameters we deduce can account for all the measured properties of ${\mathrm{BaCuSi}}_{2}{\mathrm{O}}_{6}$, opening the way to a quantitative understanding of nonuniversal scaling in any modulated layered system.

We report experimental and theoretical evidence that Rb$_2$Cu$_2$Mo$_3$O$_{12}$ has a nonmagnetic tetramer ground state of a two-leg ladder comprising antiferromagnetically coupled frustrated spin-$1/2$ chains and exhibits a Haldane spin gap of emergent spin-1 pairs. Three spin excitations split from the spin-1 triplet by a Dzyaloshinskii-Moriya interaction are identified in inelastic neutron-scattering and electron spin resonance spectra. A tiny magnetic field generates ferroelectricity without closing the spin gap, indicating a novel class of ferroelectricity induced by a vector spin chirality order., Comment: main text (6 pages, 5 figures) + supplemental material (10 pages, 8 figures), to appear in Phys. Rev. B (R)

For the skyrmion-hosting intermetallic Gd$_2$PdSi$_3$ with centrosymmetric hexagonal lattice and triangular net of rare earth sites, we report a thorough investigation of the magnetic phase diagram. Our work reveals a new magnetic phase with isotropic value of the critical field for all orientations, where the magnetic ordering vector $\mathbf{q}$ is depinned from its preferred directions in the basal plane. This is in contrast to the highly anisotropic behavior of the low field phases, such as the skyrmion lattice (SkL), which are easily destroyed by in-plane magnetic field. The bulk nature of the SkL and of other magnetic phases was evidenced by specific-heat measurements. Resistivity anisotropy, likely originating from partial gapping of the density of states along $\mathbf{q}$ in this RKKY magnet, is picked up via the planar Hall effect (PHE). The PHE confirms the single-$\mathbf{q}$ nature of the magnetic order when the field is in the hexagonal plane, and allows to detect the preferred directions of $\mathbf{q}$. For field aligned perpendicular to the basal plane, several scenarios for the depinned phase (DP), such as tilted conical order, are discussed on the basis of the data., 27 pages, 12 figures (including SI)

The polychromatic incident energy measurements using chopper spectrometers at pulsed sources enables us to measure dynamics with different energy resolutions, i.e., different time-windows with a single-measurement. By increasing the possible time-window for a single-measurement, the efficiency and usefulness of such measurements is enhanced. This is achieved by allowing the crossing of trajectories of different Eis from different source pulses on the time-of-flight diagram (the interveined trajectory). We will present an actual case of the interveined trajectory on AMATERAS, a cold-neutron chopper spectrometer installed at J-PARC, together with our experience. Some of our attempts to formulate the conditions for performing polychromatic Ei measurements employing interveined trajectories are discussed. These which can be applied to existing spectrometers, and considered as design criteria for future chopper spectrometers. Further related plan of AMATERAS to improve measuring efficiency is also mentioned.

We have conducted inelastic neutron scattering measurements to investigate the crystal-electric-field (CEF) levels associated with Pr3+ 4 f 2 -electron configuration in the PrTr2X20 (Tr: transition metal, X: Al and Zn). Hybridization between conduction electrons and 4 f electrons has been deduced from the spectral widths, which is a key factor for understanding the anomalous low-temperature transport properties and the ordering phase transitions in the PrTr2X20. We also discuss structural-transition effects on local symmetries of the Pr-ion sites.

As one of the features in the sample environment (SE) in Japanese neutron scattering facilities, some SE equipment that are frequently used at an instrument, such as the closed-cycle refrigerator (...

J-PARC, Japan Proton Accelerator Research Complex provides short pulse proton beam at a repetition rate 25Hz and the maximum power is expected to be 1MW. Materials and Life Science Experimental Facility (MLF) has 23 neutron beam ports and 21 instruments have already been operated or under construction/commissioning. There are 6 inelastic/quasi-elastic neutron scattering spectrometers and the complementary use of these spectrometers will open new insight for life science.This article is part of a Special Issue entitled “Science for Life” Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.

Magnetic excitations of the effective spin $S=1/2$ dimerized magnet ${\mathrm{Ba}}_{2}{\mathrm{CoSi}}_{2}{\mathrm{O}}_{6}{\mathrm{Cl}}_{2}$ have been probed directly via inelastic neutron scattering experiments at temperatures down to 4 K. We observed five types of excitation at 4.8, 5.8, 6.6, 11.4, and 14.0 meV, which are all dispersionless within the resolution limits. The scattering intensities of the three low-lying excitations were found to exhibit different $\mathbit{Q}$ dependencies. Detailed analysis has demonstrated that ${\mathrm{Ba}}_{2}{\mathrm{CoSi}}_{2}{\mathrm{O}}_{6}{\mathrm{Cl}}_{2}$ is a two-dimensional spin dimer system described only by a single dimer site, where the triplet excitations are localized owing to the almost perfect frustration of the interdimer exchange interactions and the undimerized spins, even in small concentration, make an essential contribution to the excitation spectrum.

We report neutron scattering measurements of single-crystalline YFe_{2}Ge_{2} in the normal state, which has the same crystal structure as the 122 family of iron pnictide superconductors. YFe_{2}Ge_{2} does not exhibit long-range magnetic order but exhibits strong spin fluctuations. Like the iron pnictides, YFe_{2}Ge_{2} displays anisotropic stripe-type antiferromagnetic spin fluctuations at (π, 0, π). More interesting, however, is the observation of strong spin fluctuations at the in-plane ferromagnetic wave vector (0, 0, π). These ferromagnetic spin fluctuations are isotropic in the (H, K) plane, whose intensity exceeds that of stripe spin fluctuations. Both the ferromagnetic and stripe spin fluctuations remain gapless down to the lowest measured energies. Our results naturally explain the absence of magnetic order in YFe_{2}Ge_{2} and also imply that the ferromagnetic correlations may be a key ingredient for iron-based materials.

Magnetic excitations of the effective spin S=1/2 dimerized magnet Ba_{2}CoSi_{2}O_{6}Cl_{2} have been probed directly via inelastic neutron scattering experiments at temperatures down to 4 K. We observed five types of excitation at 4.8, 5.8, 6.6, 11.4, and 14.0 meV, which are all dispersionless within the resolution limits. The scattering intensities of the three low-lying excitations were found to exhibit different Q dependencies. Detailed analysis has demonstrated that Ba_{2}CoSi_{2}O_{6}Cl_{2} is a two-dimensional spin dimer system described only by a single dimer site, where the triplet excitations are localized owing to the almost perfect frustration of the interdimer exchange interactions and the undimerized spins, even in small concentration, make an essential contribution to the excitation spectrum.

Spin correlations of the frustrated pyrochlore oxide ${\mathrm{Tb}}_{2+x}{\mathrm{Ti}}_{2\ensuremath{-}x}{\mathrm{O}}_{7+y}$ have been investigated by using inelastic neutron scattering on single-crystalline samples ($x=\ensuremath{-}0.007,0.000,$ and 0.003), which have the putative quantum-spin-liquid (QSL) or electric-quadrupolar ground states. Spin correlations, which are notably observed in nominally elastic scattering, show short-range correlations around $L$ points $[\mathbit{q}=(\frac{1}{2},\frac{1}{2},\frac{1}{2})]$, tiny antiferromagnetic Bragg scattering at $L$ and $\mathrm{\ensuremath{\Gamma}}$ points, and pinch-point-type structures around $\mathrm{\ensuremath{\Gamma}}$ points. The short-range spin correlations were analyzed using a random-phase approximation (RPA) assuming the paramagnetic state and two-spin interactions among Ising spins. These analyses have shown that the RPA scattering intensity well reproduces the experimental data using temperature- and $x$-dependent coupling constants of up to tenth-neighbor site pairs. This suggests that no symmetry breaking occurs in the QSL sample and that a quantum treatment beyond the semiclassical RPA approach is required. Implications of the experimental data and the RPA analyses are discussed.

Superconductivity mediated by phonons is typically conventional, exhibiting a momentum-independent s-wave pairing function, due to the isotropic interactions between electrons and phonons along different crystalline directions. Here, by performing inelastic neutron scattering measurements on a superconducting single crystal of Sr0.1Bi2Se3, a prime candidate for realizing topological superconductivity by doping the topological insulator Bi2Se3, we find that there exist highly anisotropic phonons, with the linewidths of the acoustic phonons increasing substantially at long wavelengths, but only for those along the [001] direction. This observation indicates a large and singular electron-phonon coupling at small momenta, which we propose to give rise to the exotic p-wave nematic superconducting pairing in the MxBi2Se3 (M = Cu, Sr, Nb) superconductor family. Therefore, we show these superconductors to be example systems where electron-phonon interaction can induce more exotic superconducting pairing than the s-wave, consistent with the topological superconductivity., Superconductivity mediated by phonons is usually conventional due to isotropic electron-phonon coupling. Here, Wang et al. report highly anisotropic phonons only along [001] direction in Sr0.1Bi2Se3, indicating a singular electron-phonon coupling which favors a p-wave nematic superconductivity scenario.

Hydration water is essential for a protein to perform its biological function properly. In this study, the dynamics of hydration water around F-actin and myosin subfragment-1 (S1), which are the partner proteins playing a major role in various cellular functions related to cell motility including muscle contraction, was characterized by incoherent quasielastic neutron scattering (QENS). The QENS measurements on the D2O- and H2O-solution samples of F-actin and S1 provided the spectra of hydration water, from which the translational diffusion coefficient (DT), the residence time (τT), and the rotational correlation time (τR) were evaluated. The DT value of the hydration water of S1 was found to be much smaller than that of the hydration water of F-actin while the τT values were similar between S1 and F-actin. On the other hand, the τR values of the hydration water of S1 was found to be larger than that of the hydration water of F-actin. It was also found that the DT and τR values of the hydration water of F-actin are similar to those of bulk water. These results suggest a significant difference in mobility of the hydration water between S1 and F-actin: S1 has the typical hydration water, the mobility of which is reduced compared with that of bulk water, while F-actin has the unique hydration water, the mobility of which is close to that of bulk water rather than the typical hydration water around proteins., Highlights • Hydration water dynamics of F-actin and myosin S1 was studied by neutron scattering. • Both translational and rotational motions are higher for F-actin hydration water. • Mobility of F-actin hydration water is close to that of bulk water. • High mobility of F-actin hydration water would promote the actomyosin interaction.

We investigated the low-energy incommensurate (IC) magnetic fluctuations in Sr$_2$RuO$_4$ by the high-resolution inelastic neutron scattering measurements and random phase approximation (RPA) calculations. We observed a spin resonance with energy of $\hbar\omega_\text{res}=0.56$~meV centered at a characteristic wavevector $\mathbf{Q}_\text{res}=(0.3, 0.3, 0.5)$. The resonance energy corresponds well to the superconducting gap $2\Delta=0.56$~meV estimated by the tunneling spectroscopy. The spin resonance shows the $L$ modulation with a maximum at around $L = 0.5$. The $L$ modulated intensity of the spin resonance and our RPA calculations indicate that the superconducting gaps regarding the quasi-one-dimensional $\alpha$ and $\beta$ sheets at the Fermi surfaces have the horizontal line nodes. These results may set a strong constraint on the pairing symmetry of Sr$_2$RuO$_4$. We also discuss the implications on possible superconducting order parameters., Comment: arXiv admin note: substantial text overlap with arXiv:1904.01234

Solid-state refrigeration technology based on caloric effects are promising to replace the currently used vapor compression cycles. However, their application is restricted due to limited performances of caloric materials. Here, we have identified colossal barocaloric effects (CBCEs) in a class of disordered solids called plastic crystals. The obtained entropy changes are about 380 J kg-1 K-1 in the representative neopentylglycol around room temperature. Inelastic neutron scattering reveals that the CBCEs in plastic crystals are attributed to the combination of the vast molecular orientational disorder, giant compressibility, and high anharmonic lattice dynamics. Our study establishes the microscopic scenario for CBCEs in plastic crystals and paves a new route to the next-generation solid-state refrigeration technology., Comment: four figures and supplementary materials

The ground states of the frustrated pyrochlore oxide Tb$_{2+x}$Ti$_{2-x}$O$_{7+y}$ have been studied by inelastic neutron scattering experiments. Three single-crystal samples are investigated; one shows no phase transition ($x=-0.007, Comment: 7 pages, 4 figures