Search

SUMMARY Deep long-period earthquakes (DLPs) are the major seismic events in the lower crust and can provide important information on the evolution of the Earth. To capture any fluid-related diffusive phenomena, we attempted to translate the swarm-like nature of DLPs into a diffusive one by modifying the epidemic-type aftershock sequence (ETAS) model, which is a standard tool for evaluating seismicity. The modified ETAS model explained the seismicity of DLPs in eastern Shimane, Japan successfully. The diffusional migration rate may not be as high as the rupture velocity of ordinary earthquakes, but it is still sufficient to associate slow deformation with low-frequency seismic radiation. The principal mechanical process of DLPs is likely shear slip, since the observed diffusivity (103–105 m2/s) is much larger than estimates for shallow volcanic events (100–101 m2/s), but close to those of tectonic tremors (104–105 m2/s). While the areal extent of aseismic slips is greater on the plate interface than in a less-mature system at volcanic roots, tectonic low-frequency earthquakes tend to be smaller than volcanic DLPs. The concept that seismic patches cause these earthquakes via universal diffusive shear slips can independently explain this paradox.

Fault rupture has various complexity in space and time. The temporal complexity could be expressed by the radiated energy enhancement factor (Ye et al., 2018), which is the ratio of the radiated energy to its theoretical minimum value. Regarding the spatial complexity, the rupture directivity has been well investigated from small scales (Boatwright 2007; Kane et al., 2013; Ross and Ben-Zion, 2016) to large scales (e.g. Ide and Takeo, 1997; Ruiz et al., 2016) by investigating the azimuthal dependency of dominant frequency or estimating the source process. While these studies focus on the spatiotemporal complexity of the entire fault rupture, the mesoscopic scale rupture complexity also exists through the rupture propagation, which is an important perspective of the rupture mechanics. Specifically, we can classify the rupture propagation into two endmembers: mode-II and -III ruptures. In this regard, we focused on the rupture propagations at the scale of subfault extracted from the waveform inversion.In this study, we analyzed multiple M6-class inland earthquakes in Japan using waveform inversion with the radiation-corrected empirical Green’s functions (Shibata et al., 2022), which enable us to estimate slip distributions with slip directions by synthesizing the EGF waveforms for any focal mechanisms. Then, we introduced rupture-mode intensity to evaluate the rupture-mode preferences by comparing the rupture propagation direction with the slip direction for each earthquake. As a result, we confirmed that the rupture preferentially propagated parallel (mode II) or perpendicular (mode III) to the slip direction, which is expected from the fracture mechanics. In addition, the characteristic of rupture propagation at the early stage was similar to that during the entire rupture, implying that most rupture characteristics are determined at the early stage.

Deep low-frequency earthquakes (LFEs) in Northeast Japan occur beneath active volcanoes at depths of 20-40 km. LFEs radiate low-frequency seismic waves, with most energy at 2-8 Hz, despite their lo...

SUMMARYNumerous efforts have been made to accurately estimate Green's functions, which link observed seismic waves to physical source processes. Detailed a priori information is required for the theoretical Green's function calculated from a given velocity structure. In contrast, the empirical Green's function (EGF) obtained from seismograms of nearby earthquakes with similar focal mechanisms requires the occurrence of such appropriate events. To partially release these constraints, we propose radiation-corrected EGF by correcting the radiation patterns of the EGF seismograms. In this study, we performed synthetic tests to quantify the applicability of radiation correction, together with its limitations. Such tests are a useful approach to test a benchmark of EGF applicability. We then applied the new method to real earthquakes to validate the concept for practical use. The synthetic test and real applications confirmed the superiority of the radiation-corrected EGF over the conventional EGF in specific, but realistic, cases.

The 2016 M_w 6.2 Tottori earthquake occurred on 21 October 2016 and produced thousands of aftershocks. Here we analyze high-resolution-relocated seismicity together with source properties of the mainshock to better understand the rupture process and energy budget. We use a matched-filter algorithm to detect and precisely locate >10,000 previously unidentified aftershocks, which delineate a network of sharp subparallel lineations exhibiting significant branching and segmentation. Seismicity below 8 km depth forms highly localized fault structures subparallel to the mainshock strike. Shallow seismicity near the main rupture plane forms more diffuse clusters and lineations that often are at a high angle (in map view) to the mainshock strike. An empirical Green's function technique is used to derive apparent source time functions for the mainshock, which show a large amplitude pulse 2–4 s long. We invert the apparent source time functions for a slip distribution and observe a ~16 km^2 patch with average slip ~3.2 m. 93% of the seismic moment is below 8 km depth, which is approximately the depth below which the seismicity becomes very localized. These observations suggest that the mainshock rupture area was entirely within the lower half of the seismogenic zone. The radiated seismic energy is estimated to be 5.7 × 10^(13) J, while the static stress drop is estimated to be 18–27 MPa. These values yield a radiation efficiency of 5–7%, which indicates that the Tottori mainshock was extremely dissipative. We conclude that this inefficiency in energy radiation is likely a product of the immature intraplate environment and the underlying geometric complexity.

Hydrology is important for glacier dynamics, but it is difficult to monitor the subsurface drainage systems of glaciers by direct observations. Since meltwater drainage generates seismic signals, passive seismic analysis has the potential to be used to monitor these processes. To study continuous seismic radiation from the drainage, we analyze geophone data from six stations deployed at the Kaskawulsh Glacier in Yukon, Canada, during the summer of 2014 using ambient noise cross-correlation techniques. We locate the noise sources by back-projecting the amplitude of the cross-correlation to the glacier surface. Most of the ambient noise sequences are found in two clusters, with each cluster located in the vicinity of a moulin identified at the surface. Stronger seismic radiation is observed during the day, consistent with expected variability in melt rates. We demonstrate that the sparse seismic network array with 2-km station separation has the ability to detect moulins within the array with a precision of 50 m. We confirm that seismic activity is correlated with air temperature, and thus melt, on a diurnal timescale, and precipitation correlates with the activity at longer timescales. Our results highlight the potential of passive seismic observations for monitoring water flow into subglacial channels through moulins with an affordable number of seismic stations, but quantification of water flow rates still remains a challenge. The cross-correlation back-projection technique described here can also potentially be applied to any localized source of ambient noise such as ocean noise, tectonic tremor, and volcanic tremor.

International audience

Aim Cefepime, a fourth-generation cephalosporin, acts as a GABAA receptor antagonist. Cefepime-induced encephalopathy (CIE) is frequently overlooked. We aimed to clarify the clinical features, characteristic electroencephalography (EEG), and mechanisms of CIE to aid in its early recognition. Methods CIE cases documented by a single-center consultation-liaison team between April 2015 and March 2017 were retrospectively reviewed. For further investigation, neural mass modeling was performed in silico. Results Three patients with CIE refused medication/examination and showed overt pain, palilalia, and much greater deterioration of eye and verbal response than the motor response, which was possibly related to GABAergic dysfunction. Triphasic wave-like generalized periodic discharges with a high negative component (Tri-HNC) were identified on the EEG of all three cases. The simulation reproduced the characteristic feature of 2-3 Hz Tri-HNC and recovery course on EEG, and a possible involvement of individual differences in pharmacological intervention. It also suggested that auto-inhibition (synaptic inputs from interneuron to interneuron) dysregulation contributed to generating Tri-HNC in CIE. Conclusion As CIE is iatrogenic and continues unless cefepime is stopped, early recognition is crucial. Physicians should be vigilant about altered mental status, pain, and verbal changes in patients taking cefepime. Tri-HNC on EEG can expedite the diagnosis of CIE, and the association between Tri-HNC and CIE suggests that an excitatory and inhibitory imbalance due to the dysfunction of GABAergic interneurons is the underlying mechanism. This modeling may offer a new method of investigating disorders related to GABAergic dysfunction.

Rapid estimates of earthquake rupture properties are useful for both scientific characterization of earthquakes and emergency response to earthquake hazards. Rupture directivity is a particularly important property to constrain since seismic waves radiated in the direction of rupture can be greatly amplified, and even moderate magnitude earthquakes can sometimes cause serious damage. Knowing the directivity of earthquakes is important for ground shaking prediction and hazard mitigation, and is also useful for discriminating which nodal plane corresponds to the actual fault plane particularly when the event lacks aftershocks or outcropped fault traces. Here, we propose a 3-D multiple-time-window directivity inversion method through direct waveform fitting, with source time functions stretched for each station according to a given directivity. By grid searching for the directivity vector in 3-D space, this method determines not only horizontal but vertical directivity components, provides uncertainty estimates, and has the potential to be automated in real time. Synthetic tests show that the method is stable with respect to noise, picking errors, and site amplification, and is less sensitive to station coverage than other methods. Horizontal directivity can be properly recovered with a minimum azimuthal station coverage of 180°, whereas vertical directivity requires better coverage to resolve. We apply the new method to the M_w 6.0 Nantou, Taiwan earthquake, M_w 7.0 Kumamoto, Japan earthquake, and M_w 4.7 San Jacinto fault trifurcation (SJFT) earthquake in southern California. For the Nantou earthquake, we corroborate previous findings that the earthquake occurred on a shallow east-dipping fault plane rather than a west-dipping one. For the Kumamoto and SJFT earthquakes, the directivity results show good agreement with previous studies and demonstrate that the method captures the general rupture characteristics of large earthquakes involving multiple fault ruptures and applies to earthquakes with magnitudes as small as M_w 4.7.

Deep long-period events (DLP events) or deep low-frequency earthquakes (deep LFEs) are deep earthquakes that radiate low-frequency seismic waves. While tectonic deep LFEs on plate boundaries are thought to be slip events, there have only been a limited number of studies on the physical mechanism of volcanic DLP events around the Moho (crust-mantle boundary) beneath volcanoes. One reasonable mechanism capable of producing their initial fractures is the effect of thermal stresses. Since ascending magma diapirs tend to stagnate near the Moho, where the vertical gradient of density is high, we suggest that cooling magma may play an important role in volcanic DLP event occurrence. Assuming an initial thermal perturbation of 400°C within a tabular magma of half width 41 m or a cylindrical magma of 74 m radius, thermal strain rates within the intruded magma are higher than tectonic strain rates of ~ 10^(−14) s^(−1) and produce a total strain of 2 × 10^(−4). Shear brittle fractures generated by the thermal strains can produce a compensated linear vector dipole mechanism as observed and potentially also explain the harmonic seismic waveforms from an excited resonance. In our model, we predict correlation between the particular shape of the cluster and the orientation of focal mechanisms, which is partly supported by observations of Aso and Ide (2014). To assess the generality of our cooling magma model as a cause for volcanic DLP events, additional work on relocations and focal mechanisms is essential and would be important to understanding the physical processes causing volcanic DLP events.

[1] Deep low-frequency earthquakes (LFEs) are small earthquakes (M

In western Japan, relatively small (M The present paper characterizes the seismicity of the three types of LFEs in five regions based on a more complete catalog, thanks to automated event detection and precise relocation using waveform correlation. The results show that isolated intraplate LFEs are more similar to volcanic LFEs than to tectonic LFEs. The volcanic and isolated intraplate LFEs are insensitive to tidal stress, are characterized by power-law magnitude frequency statistics such as the Gutenberg–Richter relation, and are distributed mainly in small vertical clusters, while the tectonic LFEs are modulated by tidal stress, are limited in size, and are distributed along the plate boundary. Hence, we propose that isolated intraplate LFEs should be named “semi-volcanic” LFEs. Since tectonic LFEs and volcanic LFEs are thought to be related to the fluid existence and fluid movements, respectively, isolated intraplate (semi-volcanic) LFEs may be related to crustal fluid movements in the source area.

Dynamical properties of protonic conductor K3H(SeO4)2 were examined by using various techniques, Brillouin scattering, quasi elastic, and inelastic neutron scattering. No significant anomaly was observed in longitudinal and transverse acoustic modes. In each experiment, a Lorentzian shaped spectrum was observed at extremely low energy, (less than 0.1 meV). The spectra in Brillouin and inelastic neutron scattering at the zone boundary originate from rotational modes of SeO4 tetrahedra at Г- and L-point, respectively. The peak positions, shapes, and widths of the spectra are consistent with each other, while the integrated intensities show complementary temperature dependence. The lifetimes of those modes, about 10−10 s, agree with the stationary time of conduction protons obtained from Q dependence of width in quasi elastic neutron scattering.

中性子散乱実験用圧力発生装置は，汎用性のあるピストンシリンダー型圧力発生装置を中心に開発が行われ，多くのユーザーに使用されてきた。しかし，より低温，より高圧下での実験には支障がある。最近開発された，希釈冷凍機に取り付けられるピストンシリンダー型圧力発生装置及び7GPa程度以上発生できる小型キュービックアンビル発生装置について概観し，これらの装置の特性及び得られた実験結果について簡単に述べる。

The ac magnetic susceptibility, the thermal expansion and the magnetostriction were measured using a single crystalline sample of UGe2 under pressure. We find that as the field exceeds a transition field, where the system transforms from a high pressure phase ( P > P X ) into a low pressure phase ( P P X ), the superconductivity steeply collapses within a transient region arising from the pressure inhomogeneity. We also estimate an accurate value of P X in zero temperature limit and a pressure distribution around it. Using thus estimated quantity, we argue that the superconductivity (in zero magnetic field) below the critical pressure is not intrinsic but extrinsic due to the pressure inhomogeneity.

Effects of pressure on the physical properties are very important for understanding highly correlated electron systems, in which pressure-induced attractive phenomena such as superconductivity and magnetically ordered non-Fermi liquid have been observed. Up to now, many scientists have developed a lot of high pressure apparatus for each purpose. In this paper, we present the very small “palm cubic-anvil high-pressure apparatus” for precise electric transport measurements under high pressure up to 8 GPa. The most outstanding characteristic of this pressure cell is its compactness. This cell enables us to measure absolute values of electrical resistivity, magneto-resistance and Hall coefficient at various temperatures. The details of our palm cubic high-pressure apparatus are introduced, and some neutron experimental results at room temperature are discussed.

PrPb 3 exhibits an antiferroquadrupolar transition at T Q = 0.4 K . In the present work, in order to reveal the order parameters of the ordered states in much higher fields than 5 T applied along the [1 1 ¯ 0] direction, we performed neutron diffraction experiments in the temperature range between 50 mK and 0.8 K in magnetic fields up to 14.5 T. Above 7 T, we observed magnetic reflections at q = ( δ δ 0.5 ) ( δ ∼ 0.02 ) and its equivalents. The field-induced antiferromagnetic components were normal to the applied field, indicating that the quadrupolar order parameter in the high field phase should be of O 2 2 -type.

This topical review presents results from neutron inelastic scattering experiments on single crystals of UPd2Al3. The focus is on the experimental situation, while the sequel paper advances theoretical perspectives. We present a detailed and complete characterization of the wavevector- and energy-dependent magnetization dynamics in UPd2Al3 as measured by neutron inelastic scattering primarily in the form of extensive surveys in energy–momentum space under a wide range of experimental conditions, and put our observations in context with data that has been published previously by two independent groups. In this way we emphasize the robustness of the results, which indicate the intricate nature of the dynamic magnetic susceptibility of this material. This study yields unique insight into the low-temperature ground state, which exhibits a microscopic coexistence of antiferromagnetism and superconductivity, making UPd2Al3 one of the most accessible heavy-fermion superconductors that can be fully characterized by neutron spectroscopy.

We investigated ground state properties of a heavy-fermion antiferromagnet Ce 7 Ni 3 under hydrostatic pressures and magnetic fields. This compound undergoes two antiferromagnetic phase transitions at T N1 = 1.9 K and T N2 = 0.7 K. Below T N1 , a spin-density-wave (SDW) develops. Upon applying rather weak pressure 0.39 GPa = P c , both T N1 and T N2 vanish, and non-Fermi liquid behavior appears in the specific heat and magnetic susceptibility. The enhancement of residual resistivity along the a axis near P c is attributed to the increased spin fluctuations along the a axis. By applying fields B along the c axis, T N1 is suppressed and vanishes at 0.3 T. Magnetoresistance, specific-heat, and magnetization measurements revealed another field-induced magnetic (FIM) phase in the region B || c > 0.7 T and T < 0.5 K. Neutron diffraction experiments indicate that the magnetic unit cell in the c-plane for the FIM phase is treble that of the chemical unit cell. Moreover, this magnetic reflection intensity remains even in the region between the FIM phase and SDW phase. This observation indicates the presence of large spin fluctuations in the c-plane associated with the magnetic frustration, which should be responsible for the magnetic instability of Ce 7 Ni 3 .

The design and fundamental properties of a uniaxial pressure cell for use with a four-circle neutron diffractometer are reported. It is aimed at facilitating studies on the physical and/or structural properties of solids. The results obtained for a uniaxial-pressure-induced ferromagnet Sr3Ru2O7 showed that the unit cell volume increases upon applying uniaxial pressure along the c-axis.

In this letter we report on the high energy-resolution neutron scattering studies on the dynamic structure factor of the two-triplet bound states in the two-dimensional S ¼ 1=2 Shastry–Sutherland system, SrCu2(BO3)2, in the energy transfer range of 4 to 7 meV. In contrast to the earlier interpretation of the low energy-resolution results, these bound state excitations show hardly any dispersion, but do show a strong wave-vector-dependent structure factor. Although these findings are in overall agreement with the recent theoretical calculation of the 2-triplon dynamic structure factor by Knetter and Uhrig [Phys. Rev. Lett. 92 (2004) 027204], they also show distinct differences, which may be due to some symmetry-breaking terms in the Hamiltonian that are not included in the theory, such as the interdimer Dzyaloshinski–Moriya interactions recently discovered in this compound.

In this paper we would like to review the zero field inelastic neutron scattering results obtained by using both the thermal and cold neutron triple axis instrument. The first single triplet state at around 3 meV is split due to the Dzyaloshinski-Moriya (DM) inter-dimer interaction with both the out-of-plane and in-plane components. The splitting between the S z = ±1 states is of the order of 0.3 meV. The two triplets bound states also form a very flat bands at 4.9. 5.5 and 6.3 meV with finite line width of the order and/or twice of the DM splitting. Finally the higher energy range up to 13 meV can be also characterized by three rather broad, but flat bands at around 8, 10 and 12 meV with the line width roughly three times the DM splitting. These excitations can be probably assigned to three and more triplets bound state excitations.

The thermoelectric power S of a heavy-fermion superconductor CeRhSi3 has been measured at temperatures from 2.0 K to 300 K under hydrostatic pressures up to 2.7 GPa in order to clarify the Kondo effect in CeRhSi3. S exhibits a large value of up to 60 µV/K, which is characteristic of heavyfermion systems. S shows a maximum in its temperature dependence mainly due to the Kondo effect, and its maximum temperature T Smax gradually increases from 96 K at ambient pressure to 127 K at 2.7 GPa when a pressure is applied.

Inelastic neutron scattering measurements have been performed on superconducting Na x HfNCl powder samples with x = 0.27 and 0.38 (T_{c} = 22 \hspace{0.167em} K). We have observed several temperature dependent phonon anomalies, e.g. at E∼15, 29, 76, and 81 meV for the former sample. A phonon peak with E=14.5 meV at Q∼6 A-1 increases for both samples with decreasing temperature below T = 40 \hspace{0.167em} K, which is much higher than T c. The phonon peak is assigned to an ab-plane vibrational mode, E u , of chlorine and hafnium atoms, which strongly modifies the electronic band structure. The phonon anomaly is discussed in terms of carrier inhomogeneity.

The structure of Sr 3 Ru 2 O 7 was reinvestigated by a neutron diffraction and a convergent-beam electron diffraction (CBED) experiment on single crystals. The CBED experiment revealed that the space group of Sr 3 Ru 2 O 7 is Bbcb with an orthorhombic lattice with nanometer-size twin components in the crystal. Taking these observations into account, a structure analysis was carried out with the neutron data. It was found that RuO 6 -octahedrons connected each other have rotated about c -axis in the opposite direction. This result is consistent with the previous report by a powder neutron diffraction experiment.

The magnetic structure and excitation in a localized 5f system U3Pd20Si6 were studied by means of neutron scattering. Our neutron diffraction experiments on a single-domain sample uniquely determined a remarkable collinear structure due to higher-order exchange interaction. We discovered a new type of spin-flop transition with collinear coupling. The localized nature of uranium 5f electrons with a 5f2 Γ5 ground state was clearly demonstrated by the observed crystalline electric field excitation. We observed beautiful ferromagnetic and antiferromagnetic spin-wave excitation over a whole Brillouin zone. Surprisingly, however, a clear low-energy quasi-elastic component was also observed around the antiferromagnetic zone centre. This low-energy quasi-elastic response is concluded to be the excitation of the quasi-particles due to hybridization between 5f and conduction electrons. The observation of this localized and itinerant dual nature in magnetic excitation indicates the possibility of partial localization based on an itinerant and two localized 5f electrons proposed theoretically.

We discuss recent results obtained for the heavy-fermion metals UPd2Al3 and YbRh2Si2. UPd2Al3 is the first among all superconductors for which tunneling and inelastic neutron-scattering data highlight a non-phononic, i.e., magnetic-exciton mediated, pair state. YbRh2Si2 represents a model system exhibiting pronounced non-Fermi liquid effects above a weak antiferromagnetic phase transition at T N =70 mK . Upon approaching the quantum critical point (TN→0), by low doping with Ge, one observes for T K disparate behavior in the temperature dependences of both the electrical resistivity and the electronic specific heat as well as a Curie–Weiss law in the uniform magnetic susceptibility, implying uncompensated large 4f moments. These observations indicate a break up of the composite quasiparticles into their local f-spin and itinerant conduction-electron parts.

The magnetic structure of heavy-fermion antiferromagnets Ce(Ni 1- x Pd x ) 2 Ge 2 proximate to the magnetic instability has been studied by elastic neutron scattering using single crystals. For Ce(Ni 0.65 Pd 0.35 ) 2 Ge 2 , antiferromagnetic ordering with an incommensurate propagation vector q =(1/2,1/2,δ); δ∼0.16 is observed below T N =3.4 K. The integrated intensities of magnetic Bragg peaks at 1.8 K are well fitted by assuming a sine-wave-modulated structure with the amplitude 0.55±0.04 µ B and magnetic moments along [110]. For the compound very near the magnetic instability, Ce(Ni 0.90 Pd 0.10 ) 2 Ge 2 , the ordered moment is expected to be reduced to below 0.1 µ B .

We have investigated the substitution effect of YbCo2(Zn1–xTx)20 (T = Cu, Ga, and Cd) systems by using the experiments of X-ray powder diffraction (XRPD), specific heat, magnetic susceptibility, magnetization, and electrical resistivity in order to find out a material that approaches a quantum critical point by chemical pressure. The XRPD and electrical resistivity measurements clarify that the Cu-substitution makes the lattice constants shrink and keeps the magnetic electrical resistivity high, while the Ga- and the Cd-substitution show opposite relation of the Cu-substitution. However, we could not detect clear substitution effect in the specific heat, magnetic susceptibility, and magnetization measurements of Cu-substitution system within our experiments. It is necessary that to study the Cu-substitution samples that have higher x value at lower temperature.

We have measured magnetization curves and powder neutron diffraction of double-layered Ruddlesden–Popper type ruthenate Sr 3− x Ca x Ru 2 O 7 ( x =1.5, 2.0 and 3.0). The field dependence of the magnetization revealed that the transition field of metamagnetic transition along the b -axis shifted to lower fields and that the transition became broad with increasing Sr content. The slope of the magnetization curve also increased with increasing Sr content below the metamagnetic transition. These results indicate that an itinerant component is partly introduced by the Sr substitution. From the magnetic reflection, on cooling below T N , an additional reflection was observed at (0 0 1) for each x , and the amplitude increased with decreasing temperature. The observed diffraction patterns are very similar to those of Ca 3 Ru 2 O 7 . We conclude that the magnetic structure of the antiferromagnetic ordered phase is basically the same structure with that of Ca 3 Ru 2 O 7 .

High-field magnetization and neutron diffraction measurements were performed on the one-dimensional compound Ca 3 CoRhO 6 . The long-range ordered state was first observed below 90 K. A plateau at 1/3 of the saturation magnetization was observed in the magnetization curve at 70 K, indicating ferrimagnetic alignment of the ferromagnetic Ising chains. We also observed a large hysteresis originating from a spin freezing of ferromagnetic chains in the magnetization curve at 4.2 K. Based on the results of high-field magnetization and neutron diffraction measurements, a possible magnetic structure is discussed in terms of the spin frustration on the triangular lattice.

The electronic structure of heavy-fermion compounds arises from the interaction of nearly localized 4f- or 5f-shell electrons (with atomic magnetic moments) with the free-electron-like itinerant conduction-band electrons. In actinide or rare-earth heavy-fermion materials, this interaction yields itinerant electrons having an effective mass about 100 times (or more) the bare electron mass. Moreover, the itinerant electrons in UPd2Al3 are found to be superconducting well below the magnetic ordering temperature of this compound, whereas magnetism generally suppresses superconductivity in conventional metals. Here we report the detection of a dispersive excitation of the ordered f-electron moments, which shows a strong interaction with the heavy superconducting electrons. This 'magnetic exciton' is a localized excitation which moves through the lattice as a result of exchange forces between the magnetic moments. By combining this observation with previous tunnelling measurements on this material, we argue that these magnetic excitons may produce effective interactions between the itinerant electrons, and so be responsible for superconductivity in a manner analogous to the role played by phonons in conventional superconductors.

We present the results of inelastic neutron scattering experiments on quantum spin systems KCuCl 3 and SrCu 2 (BO 3 ) 2 . Both compounds show non-magnetic singlet ground state behaviour at low temperature. KCuCl 3 turns out to be a weakly coupled dimer system without any strong frustrating interdimer interactions. SrCu 2 (BO 3 ) 2 , on the other hand, should be regarded as a strongly coupled dimer system with a strong frustration originating from the orthogonal arrangement of the neighbouring dimers. The characteristics of the spin excitations in these two dimer systems are compared and discussed.

We performed inelastic neutron scattering on the 2D Shastry-Sutherland system SrCu2(11BO3)2 with an exact dimer ground state. Three energy levels at around 3, 5, and 9 meV were observed at 1.7 K. The lowest excitation at 3.0 meV is almost dispersionless with a bandwidth of 0.2 meV at most, showing a significant constraint on a single-triplet hopping owing to the orthogonality of the neighboring dimers. In contrast, the correlated two-triplet excitations at 5 meV exhibit a more dispersive behavior.

We performed neutron diffraction and magnetization measurements to reveal the nature of phase transition of a Kondo semiconductor CeOs 4 Sb 12 . Weak antiferromagnetic (AFM) reflections characterized by a wave vector q = (1 0 0) were observed, and the ordered moment value is around 0.07µ B /Ce at zero magnetic field. The AFM structure is rapidly suppressed by magnetic field of 1 T, in contrast to the transition temperature suggested to be enhanced by magnetic field. Only ferromagnetic correlation is observed above 1 T. Such drastic variation of the magnetic correlation is closely connected into the transport properties; the AFM ordered phase below 1 T and the induced ferromagnetic state above 1 T correspond to the semiconducting and metallic states, respectively.

We investigated static and dynamical properties in the three-dimensional percolating Heisenberg antiferromagnets, RbMn c Mg 1 - c F 3 , with the magnetic concentration close to the percolation threshold, c P = 0.312 , around the superlattice point well below T N . In neutron diffraction experiment, the wave number dependence of the elastic scattering component was well fitted to q - x . Magnetic fractons were also studied using inelastic neutron scattering, and the observed fractons showed the dispersion relation of q z . The determined exponents, x = 2.43 ± 0.05 and z = 2.5 ± 0.1 , were in good agreement with the fractal dimension ( D f = 2.48 ) .

We report a superconducting phase diagram of the ferromagnetic superconductor UGe 2 investigated by AC magnetic susceptibility measurements. In contrast to previous phase diagrams, we found that the superconducting transition temperature and volume fraction show a “M-shaped” structure as a function of pressure. From this observation, we suggest that both of two critical points will play a crucial role in the occurrence of superconductivity in UGe 2 .

Neutron diffraction experiment was performed to investigate a nature of the ordered phase below 0.9 K of the filled skutterudite Kondo semiconductor CeOs 4 Sb 12 . We observed antiferromagnetic ordering with a tiny magnetic moment of around 0.03 μ B /f.u. characterized by the wave vector q =(1 0 0). The magnetic ordered state can be interpreted as a spin density wave formation due to the nesting of the small Fermi surface within the hybridization gap.

Neutron diffraction experiments were performed to investigate a nature of the antiferromagnetic ordered phase below T N = 1.6 K of the pressure-induced superconductor CeRhSi 3 . We observed incommensurate magnetic reflections characterized by the wave vector Q = ( ± δ , 0 , 0.5 ) ( δ ∼ 0.215 ) . The antiferromagnetic ordered state can be interpreted as a spin-density wave formation by taking account of the results on de Haas–van Alphen (dHvA) signals in CeRhSi 3 where the 4f-electrons of CeRhSi 3 are itinerant.

Inelastic neutron scattering experiments were performed on U ( Ru 1 - x Rh x ) 2 Si 2 with x = 0 and 0.02 in order to investigate the variations of the antiferromagnetic (AF) fluctuations with doping Rh. We have found that the energy of the magnetic excitation observed at Q = ( 1 , 0 , 0 ) in the hidden order (HO) phase markedly decreases from ∼ 2.6 meV ( x = 0 ) to ∼ 0 ( x = 0.02 ) with increasing x . In addition, the staggered susceptibility χ Q estimated from the inelastic peak develops in the HO phase at x = 0.02 , while it is suppressed at x = 0 . These results indicate that the AF fluctuation in the HO phase is significantly enhanced with doping Rh.

In the high temperature superconductor La 1.85 Sr 0.15 Cu 1 - y Zn y O 4 , we directly observed modulated antiferromagnetic correlations of Cu spin orientations via elastic ( y = 0.02 ) and low energy inelastic ( y = 0.004 ) magnetically scattered neutron intensity. A magnetic field was applied perpendicular to the CuO 2 plane to change these correlations. For y = 0.02 we confirmed an earlier observation of elastic scattered intensity at 2 K and 0 T. The component of the magnetic moment perpendicular to the scattering vector is μ ⊥ Q 0.065 μ B , and is enhanced by 32% when a 5.5 T field is applied. For y = 0.004 , we observed a 145% enhancement of 3 meV spin excitations when a 14.5 T magnetic field is applied at 1.6 K. However, we observed no elastic scattered intensity at either 0 or 14.5 T.

We have performed neutron scattering experiments to investigate the static magnetic structure and the magnetic critical scattering in the three-dimensional percolating Heisenberg antiferromagnet, RbMn 0.31 Mg 0.69 F 3 , whose magnetic concentration is just at the percolation concentration for a cubic lattice, c P = 0.312 . Magnetic scattering was observed around the superlattice point, ( 1 2 , 1 2 , 1 2 ) . We determined the Neel temperature of this system to be T N = 4.0 ± 0.5 K , and found that the critical scattering above T N is similar to that observed in the homogeneous system. At T = 1.6 K well below T N , the scattering function is described by a sum of the critical scattering and elastic scattering components, and we demonstrated that the q -variation of the intensity of the elastic scattering component can be described using the fractal dimension.

We performed neutron diffraction experiments on PrPb 3 in a [001] magnetic field to examine the quadrupolar ordering structure. In magnetic fields, antiferromagnetic moments with q =(½ ±δ ½ 0) and (½ ½ ±δ 0) (δ∼\frac{1}{8}) are observed below T Q whose amplitudes linearly vary with H and vanish at zero field, providing the first evidence of a long periodic quadrupolar structure. The field induced magnetic structure is a sinusoidal one, and the direction of the magnetic moments is parallel to the magnetic field; the order parameter must be the quadrupole O 2 0 . We attribute this quadrupole structure to the indirect RKKY-type interaction between the quadrupoles. Moreover, for H

Synchrotron radiation x-ray diffraction experiments on the pressure-induced ferromagnetic superconductor UGe 2 has been performed using a diamond anvil cell (DAC) diffractometer to study the correlation between the crystal structure and ferromagnetism. The oscillation photos covering the three-dimensional reciprocal spaces were taken both below and above a critical temperature T x at pressures up to 1.1 GPa. Coupled charge density wave (CDW) and spin density wave (SDW) fluctuations were predicted as an origin of unusual properties of UGe 2 by Watanabe and Miyake, but no additional superlattice Bragg peaks corresponding to the CDW reflections could be observed, resulting in an upper limit of its intensity of ∼1 ×10 -4 to the fundamental Bragg peak intensity.

The cubic intermetallic compound PrPb 3 is considered to exhibit an antiferro-quadrupolar (AFQ) ordering at T Q = 0.4 K . We have performed neutron diffraction experiments on PrPb 3 in order to detect a possible induced antiferromagnetic (AFM) moment in the AFQ phase. At T = 40 mK , a small magnetic reflection q = ( 1 2 δ δ ) with δ = 0.062 is observed above 3 T. The emergence of the magnetic reflection is accompanied by a large hysteresis, implying the transition to be of first order. The direction of the AFM component ( | | [ 1 1 0 ] ) suggests an underlying AFQ order of O 2 2 type.