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Selected ancient Greek bronze coins held in the Coin Collection of the Kunsthistorisches Museum Vienna (KHM) were studied concerning their preservation and conservation. The coins had been minted during the Roman Imperial time (50 to 280 AD) using alloys with high lead and/or tin contents. Today a number of these highly leaded bronze coins, altogether different singular pieces, show progressive whitish corrosion in spots or well-defined areas on their surfaces. Different analytical techniques were used for the documentation and study of the different states of corrosion, the corrosion phases developing in the whitish parts as well as the cause of the specific corrosion phenomena. Further studies focused on the analysis of the corrosion phases – combining results from μ-XRD and neutron diffraction investigations – as well as on the manufacturing techniques of the antique Greek coins. The μ-XRD analysis applied a beam spot of 300 μm allowing for a localised determination of corrosion phases on the surfaces of the objects. The main corrosion products consist of metal (Cu, Pb, Cu/Sn) oxide phases. As minor components also metal sulphide and chloride phases could be assigned. To enable the distinction between different manufacturing techniques 35 coins and eight self-made ‘replicas’ were analysed in a non-destructive way by bulk neutron texture analysis which reveals changes in the microcrystalline structure of the alloys related to the mechanical minting processes.

We report the low-temperature properties of phase-pure single crystals of the half-Heusler compound CuMnSb grown by means of optical float-zoning. The magnetization, specific heat, electrical resistivity, and Hall effect of our single crystals exhibit an antiferromagnetic transition at $T_{\mathrm{N}} = 55~\mathrm{K}$ and a second anomaly at a temperature $T^{*} \approx 34~\mathrm{K}$. Powder and single-crystal neutron diffraction establish an ordered magnetic moment of $(3.9\pm0.1)~\mu_{\mathrm{B}}/\mathrm{f.u.}$, consistent with the effective moment inferred from the Curie-Weiss dependence of the susceptibility. Below $T_{\mathrm{N}}$, the Mn sublattice displays commensurate type-II antiferromagnetic order with propagation vectors and magnetic moments along $\langle111\rangle$ (magnetic space group $R[I]3c$). Surprisingly, below $T^{*}$, the moments tilt away from $\langle111\rangle$ by a finite angle $\delta \approx 11^{\circ}$, forming a canted antiferromagnetic structure without uniform magnetization consistent with magnetic space group $C[B]c$. Our results establish that type-II antiferromagnetism is not the zero-temperature magnetic ground state of CuMnSb as may be expected of the face-centered cubic Mn sublattice., Comment: 14 pages, 15 figures

We report selected experimental results on the spin dynamics and spin freezing at ferromagnetic quantum phase transitions to illustrate some of the most prominent escape routes by which ferromagnetic quantum criticality is avoided in real materials. In the transition metal Heusler compound Fe2TiSn we observe evidence for incipient ferromagnetic quantum criticality. High pressure studies in MnSi reveal empirical evidence for a topological non-Fermi liquid state without quantum criticality. Single crystals of the hexagonal Laves phase compound Nb1−y Fe2+y provide evidence of a ferromagnetic to spin density wave transition as a function of slight compositional changes. Last but not least, neutron depolarisation imaging in CePd1−x Rh x underscore evidence taken from the bulk properties of the formation of a Kondo cluster glass.

Kurzfassung Die Restaustenit-Analyse mittels Röntgen-Beugungsverfahren wird häufig nach standardisierten Verfahren wie ASTM E975-03 [1] oder SAE-SP-452 [2] durchgeführt. Die Verfahren basieren auf der Analyse der integralen Intensitätsverhältnisse von wenigen Beugungsreflexen für die einzelnen Phasen. Die Anpassung erfolgt modellfrei bezüglich der unterliegenden strukturellen Phasen. Dabei ist die genaue Kenntnis der Mikrostruktureigenschaften (Texturierungen, Eigenspannungszustände), die sich empfindlich auf die Intensitäten der Beugungsreflexe auswirken können, und ein geringer Anteil an weiteren Phasen, beispielsweise Carbiden, eine notwendige Voraussetzung. Dies trifft für technologisch relevante Proben häufig nicht zu. Als Folge sind daher oftmals große Streubreiten der Restaustenitgehalte bei den standardisierten Analysen zu beobachten, siehe z. B. [3]. Im vorliegenden Artikel wird ein Vergleich zwischen dem standardisierten Verfahren und einer Analyse unter Verwendung einer durch Strukturmodelle gestützten Gesamtprofilanpassung für exemplarische Proben mit leichten Vorzugsorientierungen und für den Einsatz von 1-D- und 2-D-Detektoren vorgestellt.

Stresses in the near-surface area can form cracks which join together, propagate and combine, forming pits due to material spall-off. The stresses causing the cracks are not only influenced by external forces, residual stresses stored in the material also play an important role. Moreover, these residual stresses can vary during the lifetime of the sliding components. Cracks are found in the wear tracks of linear oscillating ball contacts on AISI 4140 steel. The crack propagation at the surface is longitudinal to the sliding direction. Residual stress analysis by X-ray diffraction (XRD) shows that normalized samples develop tensile stresses in the near-surface zone of the wear track. Residual stresses are found to be higher transversal to the moving direction than longitudinal.

Hradil K., Psota V., Stastna P. (2013): Species diversity of true bugs on apples in terms of plant protec tion. Plant Protect. Sci., 49: 73– 83. Monitoring of species spectrum of true bugs (Heteroptera) on apple trees without pest management was conducted in 2010–2011. Two sites were selected – an abandoned orchard and a road alley near the village of Velke Bilovice (Břeclav district, Czech Republic). The capture of true bugs with a fogger device (Pulsfog) on five selected trees in each site was performed. The effective substance deltamethrin at concentration of 0.0025 g/l was applied to the tree crowns. Three collections (28/4, 20/5, and 9/7) in 2010 and two (11/5 and 23/6) in 2011 were done. Out of 55 detected spe cies of true bugs, 43 species occurred in the alley and 29 in the orchard. Thirty-two species were predatory or partly predatory (58.18%), 22 species were phytophagous (40%), and one mycetophagous (1.82%).

Phonons in a metal interact with conduction electrons which give rise to a finite linewidth. In the normal state, this leads to a Lorentzian shape of the phonon line. Density functional theory is able to predict the phonon linewidths as a function of wave vector for each branch of the phonon dispersion. An experimental verification of such predictions is feasible only for compounds with very strong electron-phonon coupling. YN2B2C was chosen as a test example because it is a conventional superconductor with a fairly high T c (15.2 K). Inelastic neutron scattering experiments did largely confirm the theoretical predictions. Moreover, they revealed a strong temperature dependence of the linewidths of some phonons with particularly strong electron-phonon coupling which can as yet only qualitatively be accounted for by theory. For such phonons, marked changes of the phonon frequencies and linewidths were observed from room temperature down to 15 K. Further changes were observed on entering into the superconducting state. These changes can, however, not be described simply by a change of the phonon linewidth.

For stabilized nanoparticles of cadmium sulfide, a highly resolved radial distribution function was derived from the dispersion curve of synchrotron radiation (λ = 0.08824 A). The nanoparticle core has dimensions of 15 A–20 A and consists of Cd and S atoms in a 1:1 ratio. In the inner part of the nanoparticle, these atoms have a random tetrahedral coordination similar to that in crystalline CdS. Half of all core S atoms belong to the ligands and are coordinated by the surface Cd atoms. In contrast to the inner S atoms, these S atoms each binds two or three Cd atoms, forming a CdSCd bond angle of ≈100°, which is smaller than the tetrahedral angle. The Cd-S bond lengths are similar for both types of sulfur and vary within 2.52 A–2.53 A. The spatial arrangement of the Cd and S atoms beyond the first coordination sphere is significantly different from that of bulk CdS, which may be caused by perturbations induced by the surface S atoms.

Using high-energy synchrotron radiation, powder diffraction experiments were carried out on CdS nanocrystals stabilized with glutathione. The radial distribution function was calculated from the data and analysed. The nanoparticle core, of diameter estimated as 15–20 Å, consists of Cd and S atoms in the proportion 1:1. Inside the core, both Cd and S atoms coordinate each other approximately tetrahedrally. The surface S atoms are connected to just two or three Cd atoms of the core and belong to the glutathione molecules of the particle shell. These S atoms are also a part of the core structure and contribute about one half of the total number of S atoms per particle. First-neighbour Cd—S distances are 2.523 Å with a narrow distance distribution. No difference is observed between the lengths of Cd—S bonds involving the sulfur of the glutathione molecules and the sulfur atoms which are solely bound to Cd. The bond angle Cd—S—Cd at the surface bridging S atoms of glutathione isca99.5°,i.e.significantly smaller than an average one of 109.5° characteristic of the Cd and S atom packing inside the core. Beyond the range of the near interatomic distances, the influence of the surface and the defects cause a significant distinction of the particle core structure from those of zincblende and wurtzite, characteristic of bulk CdS.

Cd 1-x Mn x Te crystals, obtained by the high-pressure Bridgman method for x = 0, 0.27, 0.49, 0.67 and 0.8, were investigated. Crystal composition was determined by electron microprobe analysis. For an Mn content lower than 0.7, a single phase of pure zinc blend structure was found. In Cd 0.2 Mn 0.8 Te samples a two-phase structure was revealed. Auger electron spectroscopy (AES) was used to determine the composition of the crystal surfaces. AES depth profiles obtained by argon sputtering and AES analysis allowed to find the distribution of Cd, Mn and Te inside the sub-surface region. Spectroscopic ellipsometry was applied to determine the complex dielectric function e of the samples. Ellipsometric measurements were performed at room temperature in the photon energy range 0.75-6.5 eV. The spectral dependence of e was used to find the energy gaps E g of the alloys with different Mn content. Ellipsometric data were correlated with the compositional results obtained from the electron microprobe and AES depth profile investigations. A linear increase of energy gaps with increasing x was observed for chemically homogeneous CdMnTe crystals.

Disordered decagonal quasicrystals with the nominal compositions Al 72 Ni 12 Co 16 and Al 72.5 Ni 11 Co 16.5 were investigated by comparative diffuse neutron (N) and X-ray (X) synchrotron studies, respectively, at temperatures up to 1000 °C. High resolution X-ray measurements reveal peak splitting consistent with a domain structure of 2D qp and 1D qp lamellae. At higher temperatures the strain fluctuations decrease, giving rise to larger areas of the 2D qp and 1D qp domains. In summary, this disordered Al–Co–Ni phase is governed by complex transient ordering states, i.e. twinned lamellar domains of true 2D qc sequences, 1D and periodic domains accompanied by phason straining and phason fluctuations.

Diffuse layers corresponding to an 8 A superperiod along the ‘periodic’ axis of decagonal Al–Ni–Co phases were investigated by in situ X-ray and neutron diffraction at temperatures up to 980 °C. The diffuse layers consist of an unstructured diffuse background, diffuse bands, and diffuse maxima which (almost) all vanish above 900 °C, but show a different temperature dependence in detail. A tentative scenario of the related structural ordering process during cooling from high temperature is developed. A 1D-columnar cluster model is compared to the experimental results.

We present a combined density functional perturbation theory and inelastic neutron scattering study of the lattice dynamical properties of YNi${}_{2}$B${}_{2}$C. In general, very good agreement was found between theory and experiment for both phonon energies and line widths. Our analysis reveals that the strong coupling of certain low energy modes is linked to the presence of large displacements of the light atoms, i.e., B and C, which is unusual in view of the rather low phonon energies. Specific modes exhibiting a strong coupling to the electronic quasiparticles were investigated as a function of temperature. Their energies and line widths showed marked changes on cooling from room temperature to just above the superconducting transition at ${T}_{c}$ = 15.2 K. Calculations simulating the effects of temperature allow us to model the observed temperature dependence qualitatively.

The increasing worldwide energy consumption calls for the design of more efficient energy systems. Thermoelectrics could be used to convert waste heat back to useful electric energy if only more efficient materials were available. The ideal thermoelectric material combines high electrical conductivity and thermopower with low thermal conductivity. In this regard, the intermetallic type-I clathrates show promise with their exceedingly low lattice thermal conductivities [1]. Here we report the successful incorporation of cerium as guest atom into the clathrate crystal structure. In many simpler intermetallic compounds, this rare earth element is known to lead, via the Kondo interaction, to strong correlation phenomena including the ocurrence of giant thermopowers at low temperatures [2]. Indeed, we observe a 50% enhancement of the thermopower compared to a rare earth-free reference material. Importantly, this enhancement occurs at high temperatures and we suggest that a `rattling' enhanced Kondo interaction [3] underlies this effect., Comment: 6 pages, 4 figures

X-ray diffraction patterns of decagonal Al70Co15Ni15, Al72Ni12Co16 and Al62Cu20Co15Si3 show, apart from ’sharp’ reflections, prominent diffuse maxima and diffuse streaks. From an analysis of high-resolution synchrotron data, arguments are given in favour of a more uniform interpretation of all these phenomena in terms of linear phason strain and phason fluctuations. Thus structural modifications, including one-dimensional quasicrystalline domains and periodic domains (approximants) can be conveniently described as transient ordering states, depending on temperature and composition.

Synchrotron measurements at DESY and ESRF of decagonal quasicrystals with the nominal composition Al 70 Co 15 Ni 15 and Al 72 Co 16 Ni 12 , show that Bragg reflections with high |H i ∗ | values are surrounded by up to four weak subsidiary peaks. The positions of these additional peaks depend solely on the position of the Bragg reflection in the reciprocal perpendicular subspace and can be explained by a linear phason strain model. This model sheds new light on the current superorder models [K. Hradil et al. Phil. Mag. A 79 (1999) 1963] and is a further step towards an understanding of the real structures of decagonal quasicrystals.

Diffuse layers which are observed in different decagonal quasicrystals perpendicular to the unique ‘periodic’ axis are explained by one-dimensional (1D) columns of icosahedral A1 clusters along this axis. From results of X-ray and purely elastic neutron diffraction experiments we give a qualitative explanation by basically off-layer atomic displacements which are grossly uncorrelated in different columnar clusters. A reversible temperature behaviour of the 1D superstructure which vanishes at high temperatures can be understood in the framework of this interpretation. Diffuse intensity modulations within the diffuse layers are discussed in terms of atomic displacements and chemical ordering within the icosahedral clusters which are the basic structural units of the columns. Computer simulations of different columnar models are carried out, their Fourier transforms are compared with the observed patterns.

A 4-circle diffractometer equipped with a novel imaging system has been installed at HASYLAB beamline G3. The imaging system comprising a microchannel plate (MCP) in front of a CCD detector allows position-resolved X-ray diffraction investigations of polycrystalline materials. Alternatively, a scintillation counter behind a Soller collimator can be used. Material properties like strain and/or texture can thus be determined either position resolved using the MCP/CCD system or in an averaging mode using the Soller/scintillator combination. The field of view of the MCP/CCD system is larger than 1 cm2 with a spatial resolution down to 12 μm. Both detection systems applied are aberration free. The spatial information can be directly extracted from pictures taken by the imaging system. Together with the wide field of view this method is especially suited for the investigation of dynamical processes in polycrystalline materials.

The dynamics of the decagonal AlNiCo phase has been investigated on a single-grain quasicrystalline sample using inelastic neutron scattering. The decagonal structure can be viewed as a periodic stacking of quasiperiodic planes. The anisotropy between the modes propagating in the periodic and quasiperiodic directions is found to be much weaker than theoretically predicted. A strong resonance splitting is observed at an energy transfer of 15 meV for transverse modes polarized in the quasiperiodic plane.

The p27Kip1 gene has been identified as inductor of cell cycle arrest at the G1 checkpoint to prevent entry of somatic cells into the S phase of the cell cycle when substantial DNA damage has occurred. It has been suggested that decreased expression of the p27Kip1 protein may contribute to the development of human malignancies due to loss of critical antiproliferative mechanisms. In the present study, 95 specimens (T1–T4) from 95 randomly selected patients undergoing radical prostatectomy at the Urological Department of Hannover University (82 patients) as well as in the Josef Hospital Regensburg (13 patients) between 1981 and 1992 for whom tissue blocks for immunohistochemical investigation were available, were investigated for different biological and clinical characteristics as possible predictors for recurrence-free and long-term survival: age, depth of tumour infiltration, histological grade, lymph node status, as well as decreased expression of the p27Kip1 protein. After a median follow-up up of 56 months (24–151 months), seven of 21 (33%) patients (Group 1) with loss of p27Kip1 protein expression or a relative amount of

A single crystal of the thermodynamically stable decagonal phase in the system Al–Ni–Co with the nominal composition Al72.5Co11Ni16.5 was first studied by neutron diffraction. The diffraction experiment showed that the investigated crystal was a true single crystal. In a preliminary experiment we have measured a selection of Bragg reflections, diffuse scattering and satellite scattering and compared the observations with corresponding X-ray results. From this comparison we may conclude, that the 10mm symmetry is not due to the indiscernibility of Co and Ni atoms (X-rays), but a true structure feature. The superorder satellite scattering is basically not due to a Co/Ni ordering problem.

The magnetic excitation spectrums of charge stripe ordered La(2-x)Sr(x)NiO(4) x = 0.45 and x = 0.4 were studied by inelastic neutron scattering. We found the magnetic excitation spectrum of x = 0.45 from the ordered Ni^2+ S = 1 spins to match that of checkerboard charge ordered La(1.5)Sr(0.5)NiO(4). The distinctive asymmetry in the magnetic excitations above 40 meV was observed for both doping levels, but an additional ferromagnetic mode was observed in x = 0.45 and not in the x = 0.4. We discuss the origin of crossover in the excitation spectrum between x = 0.45 and x = 0.4 with respect to discommensurations in the charge stripe structure., 4 Figures. To be appear in the J. Kor. Phys. Soc. as a proceedings paper from the ICM 2012 conference

Commensurate satellite reflections in diffraction patterns of decagonal Al-Ni-Co and Al-Cu-Co phases indicate a periodic superorder on the quasiperiodic substructure. From the intensity characteristics of these satellites a box-like modulation function is derived which may be visualized in different ways including approximant phases. An interpretation by fine-scale periodic lamella microdomains matches closely high-resolution electron microscopy observations and characteristic structural features of the average structure.

The title compounds have an isotypic averaged structure but differ in significant detail with respect to disorder. Disorder diffuse scattering has been studied in situ up to 1150 K with a heating camera and X-ray films and an image-plate system at the synchrotron source Deutsches Elektronensynchrotron/HASYLAB. With the oscillation technique (primary beam perpendicular to the ‘periodic’ direction) the area between the zeroth and the fourth Bragg layer was explored. There are modulated diffuse layers and diffuse phenomena, in particular diffuse streaks, within the Bragg layers. The diffuse layers are related to a superperiod along the ‘periodic’ direction and the streaks arise from disorder in the quasicrystalline packing. A different temperature behaviour of the diffuse layers compared with the diffuse streaks was observed. The former decrease in intensity above 770 K and vanish completely at about 1070 K, whereas the intensity of the diffuse streaks decreases between 1120 and 1150K. Both processe...

Diffuse scattering of the thermodynamically stable decagonal quasicrystal (QC) Al70Ni15Co15 has been measured at a synchrotron radiation source. Perpendicular to the unique ‘periodic’ direction there is an alternating sequence of ‘Bragg’ and (modulated) diffuse layers. Within the zeroth Bragg layer, strong diffuse streaks and diffuse satellite reflections, as well as very weak and slowly varying diffuse scattering, were measured up to high values of Q. Satellites and diffuse streaks, already known from precession photographs, were explored in the q-scan mode yith a step width of 0.01 in h and k (pseudo-monoclinic setting with a∗ = 0.081 08 A−1, b∗ = 0.081 09 A−1 in the QC plane, c∗ = 0.245 16 A−1 in the periodic direction, y = 72°). The positions, but not the intensities of all registered satellite reflections obey an overall tenfold symqetry around the Bragg reflection. The satellite vector magnitude [sbnd]qs[sbnd] = 3.3 × 10 −2 A−1 corresponds to a translational superperiod of the QC substructu...

There exists increasing evidence that the phase diagram of the high-transition temperature (Tc) cuprate superconductors is controlled by a quantum critical point. One distinct theoretical proposal is that, with decreasing hole-carrier concentration, a transition occurs to an ordered state with two circulating orbital currents per CuO2 square. Below the 'pseudogap' temperature T* (T* > Tc), the theory predicts a discrete order parameter and two weakly-dispersive magnetic excitations in structurally simple compounds that should be measurable by neutron scattering. Indeed, novel magnetic order and one such excitation were recently observed. Here, we demonstrate for tetragonal HgBa2CuO4+d the existence of a second excitation with local character, consistent with the theory. The excitations mix with conventional antiferromagnetic fluctuations, which points toward a unifying picture of magnetism in the cuprates that will likely require a multi-band description., Including supplementary information

In this Letter, we explore the phase diagram and excitations of a distorted triangular lattice antiferromagnet. The unique two-dimensional distortion considered here is very different from the ``isosceles''-type distortion that has been extensively investigated. We show that it is able to stabilize a $120\ifmmode^\circ\else\textdegree\fi{}$ spin structure for a large range of exchange interaction values, while new structures are found for extreme distortions. A physical realization of this model is $\ensuremath{\alpha}\mathrm{\text{\ensuremath{-}}}{\mathrm{CaCr}}_{2}{\mathrm{O}}_{4}$, which has a $120\ifmmode^\circ\else\textdegree\fi{}$ structure but lies very close to the phase boundary. This is verified by inelastic neutron scattering which reveals unusual rotonlike minima at reciprocal space points different from those corresponding to the magnetic order.

We report an inelastic neutron scattering investigation of phonons with energies up to 159 meV in the conventional superconductor YNi(2)B(2)C. Using the sweep mode, a newly developed time-of-flight technique involving the continuous rotation of a single crystal specimen, allowed us to measure a four-dimensional volume in (Q, E) space and, thus, determine the dispersion surface and linewidths of the A(1g) (≈102 meV) and A(u) (≈159 meV) type phonon modes over the whole Brillouin zone. Despite of having linewidths of Γ=10 meV, A(1g) modes do not strongly contribute to the total electron-phonon coupling constant λ. However, experimental linewidths show a remarkable agreement with ab initio calculations over the complete phonon energy range, demonstrating the accuracy of such calculations in a rare comparison to a comprehensive experimental data set.

We present an inelastic neutron-scattering study of phonon line shapes in the vortex state of the type II superconductor YNi${}_{2}$B${}_{2}$C. In a previous study [Phys. Rev. Lett. 101, 237002 (2008)] it was shown that certain phonons exhibit a clear signature of the superconducting gap $2\ensuremath{\Delta}$ on entering the superconducting state. Our interest was to find out whether or not the line shape of such phonons reflects the inhomogeneous nature of the vortex state induced by a magnetic field smaller than the upper critical field ${B}_{c2}$.We found that this is indeed the case because the observed phonon line shapes can be well described by a model considering the phonon as a local probe of the spatial variation of the superconducting gap. We found that even at $B=3\phantom{\rule{0.28em}{0ex}}\mathrm{T}$, where the intervortex distance is less than $300\phantom{\rule{0.16em}{0ex}}$\AA{}, the phonon line shape still shows evidence for a variation of the gap.

In this Letter, we explore the phase diagram and excitations of a distorted triangular lattice antiferromagnet. The unique two-dimensional distortion considered here is very different from the "isosceles"-type distortion that has been extensively investigated. We show that it is able to stabilize a 120° spin structure for a large range of exchange interaction values, while new structures are found for extreme distortions. A physical realization of this model is α-CaCr(2)O(4), which has a 120° structure but lies very close to the phase boundary. This is verified by inelastic neutron scattering which reveals unusual rotonlike minima at reciprocal space points different from those corresponding to the magnetic order.

Disordered decagonal Al72Co16Ni12 quasicrystals were investigated by recording diffuse neutron scattering at instruments D10 and IN8/ILL up to 1000 °C. This neutron work supplements X-ray-diffraction investigations, which do not provide a scattering contrast of the transition metals. Moreover, diffuse scattering of inelastic origin could be suppressed, within the resolution limits, by using an analyser. The temperature dependence of the diffuse scattering in the quasiperiodic plane indicates complex re-ordering processes. A one-dimensional superorder along the unique axis, reflected by diffuse layers perpendicular to it, dissolves at 950 °C; short-range-order maxima remain visible at 980 °C.

We report an inelastic neutron scattering investigation of phonons with energies up to 159 meV in the conventional superconductor YNi(2)B(2)C. Using the sweep mode, a newly developed time-of-flight technique involving the continuous rotation of a single crystal specimen, allowed us to measure a four-dimensional volume in (Q, E) space and, thus, determine the dispersion surface and linewidths of the A(1g) (≈102 meV) and A(u) (≈159 meV) type phonon modes over the whole Brillouin zone. Despite of having linewidths of Γ=10 meV, A(1g) modes do not strongly contribute to the total electron-phonon coupling constant λ. However, experimental linewidths show a remarkable agreement with ab initio calculations over the complete phonon energy range, demonstrating the accuracy of such calculations in a rare comparison to a comprehensive experimental data set.

The field induced switching process across the ferroelectric lock-in transition in K(2)SeO(4) has been studied on a millisecond timescale using stroboscopic neutron diffraction. The time evolution of both the first and the third order satellites was examined. The time constants are found to vary with temperature between 0.2 and 1.2 ms. This is an order of magnitude faster than in the isostructural Rb(2)ZnCl(4). Moreover, the time dependence of the satellite's linewidth provides information about the evolution of the coherence of the modulated structure.

Motivated by predictions of a substantial contribution of the "buckling" vibration of the CuO(2) layers to d-wave superconductivity in the cuprates, we have performed an inelastic neutron scattering study of this phonon in an array of untwinned crystals of YBa(2)Cu(3)O(7). The data reveal a pronounced softening of the phonon at the in-plane wave vector q=(0,0.3) upon cooling below ~105 K, but no corresponding anomaly at q=(0.3,0). Based on the observed in-plane anisotropy, we argue that the electron-phonon interaction responsible for this anomaly supports an electronic instability associated with a uniaxial charge-density modulation and does not mediate d-wave superconductivity.

Neutron scattering for ${\text{Nd}}_{2\ensuremath{-}x}{\text{Ce}}_{x}{\text{CuO}}_{4+\ensuremath{\delta}}$ ($x\ensuremath{\approx}0.155$, ${T}_{c}=25\text{ }\text{K}$) reveals two distinct magnetic energy scales in the superconducting state: ${\ensuremath{\omega}}_{1}\ensuremath{\approx}6.4\text{ }\text{meV}$ and ${\ensuremath{\omega}}_{2}\ensuremath{\approx}4.5\text{ }\text{meV}$. These magnetic energies agree quantitatively with the ${B}_{1g}/{B}_{2g}$ and ${A}_{1g}$ features observed in electronic Raman scattering, where the former is believed to indicate the maximum superconducting gap and the origin of the latter has remained unexplained. The data are inconsistent with previous claims of the existence of a magnetic resonance mode near 10 meV, but consistent with a resonance at ${\ensuremath{\omega}}_{2}$ and with the recently established universal ratio of resonance energy to superconducting gap in unconventional superconductors [G. Yu et al., Nat. Phys. 5, 873 (2009)].

We study the symmetry of spin excitation spectra in 122-ferropnictide superconductors by comparing the results of first-principles calculations with inelastic neutron scattering (INS) measurements on BaFe1.85Co0.15As2 and BaFe1.91Ni0.09As2 samples that exhibit neither static magnetic phases nor structural phase transitions. In both the normal and superconducting (SC) states, the spectrum lacks the 42/m screw symmetry around the (1/2 1/2 L) axis that is implied by the I4/mmm space group. This is manifest both in the in-plane anisotropy of the normal- and SC-state spin dynamics and in the out-of-plane dispersion of the spin-resonance mode. We show that this effect originates from the higher symmetry of the magnetic Fe sublattice with respect to the crystal itself, hence the INS signal inherits the symmetry of the unfolded Brillouin zone (BZ) of the Fe sublattice. The in-plane anisotropy is temperature-independent and can be qualitatively reproduced in normal-state density-functional-theory calculations without invoking a symmetry-broken ("nematic") ground state that was previously proposed as an explanation for this effect. Below the SC transition, the energy of the magnetic resonant mode Er, as well as its intensity and the SC spin gap inherit the normal-state intensity modulation along the out-of-plane direction L with a period twice larger than expected from the body-centered-tetragonal BZ symmetry. The amplitude of this modulation decreases at higher doping, providing an analogy to the splitting between even and odd resonant modes in bilayer cuprates. Combining our and previous data, we show that at odd L a universal linear relationship Er=4.3*kB*Tc holds for all studied Fe-based superconductors, independent of their carrier type. Its validity down to the lowest doping levels is consistent with weaker electron correlations in ferropnictides as compared to the underdoped cuprates., Comment: To be published in Phys. Rev. B. 18 pages, 14 figures, including one interactive figure. References updated and supplied with hyperlinks (v3); Fig. 3 added with an interactive comparison of different Brillouin zones, introduction extended (v2)

We report an inelastic-neutron-scattering and muon-spin-relaxation study of the effect of 2% spinless (Zn) impurities on the magnetic order and dynamics of YBa(2)Cu(3)O(6.6), an underdoped high-temperature superconductor that exhibits a prominent spin pseudogap in its normal state. Zn substitution induces static magnetic order at low temperatures and triggers a large-scale spectral-weight redistribution from the magnetic resonant mode at 38 meV into uniaxial, incommensurate spin excitations with energies well below the spin pseudogap. These observations indicate a competition between incommensurate magnetic order and superconductivity close to a quantum critical point. Comparison to prior data on La(2-x)Sr(x)CuO(4) suggests that this behavior is universal for the layered copper oxides and analogous to impurity-induced magnetic order in one-dimensional quantum magnets.

We report an inelastic-neutron-scattering and muon-spin-relaxation study of the effect of 2% spinless (Zn) impurities on the magnetic order and dynamics of YBa(2)Cu(3)O(6.6), an underdoped high-temperature superconductor that exhibits a prominent spin pseudogap in its normal state. Zn substitution induces static magnetic order at low temperatures and triggers a large-scale spectral-weight redistribution from the magnetic resonant mode at 38 meV into uniaxial, incommensurate spin excitations with energies well below the spin pseudogap. These observations indicate a competition between incommensurate magnetic order and superconductivity close to a quantum critical point. Comparison to prior data on La(2-x)Sr(x)CuO(4) suggests that this behavior is universal for the layered copper oxides and analogous to impurity-induced magnetic order in one-dimensional quantum magnets.

A neutron scattering study reveals that the magnetic fluctuations in an iron arsenide superconductor behave according to the conventional theories of metals, unlike the cuprate superconductors. Moreover, the magnetic spin-excitation energies are sufficient to mediate the Cooper pairs that form the superconducting state.

Inelastic neutron-scattering measurements of single-${\text{CuO}}_{2}$-layer ${\text{HgBa}}_{2}{\text{CuO}}_{4+\ensuremath{\delta}}$ reveal an antiferromagnetic resonance with energy ${\ensuremath{\omega}}_{\text{r}}=56\text{ }\text{meV}$ $(\ensuremath{\approx}6.8{k}_{\text{B}}{T}_{\text{c}})$ below the superconducting transition temperature ${T}_{\text{c}}\ensuremath{\approx}96\text{ }\text{K}$. The resonance is energy-resolution limited and exhibits an intrinsic momentum width of about $0.2\text{ }{\text{\AA{}}}^{\ensuremath{-}1}$, consistent with prior work on several other cuprates. The rather large value of ${\ensuremath{\omega}}_{\text{r}}$ is identical to the characteristic energy of the electron-boson spectral density obtained from recent optical conductivity work, consistent with the notion that the charge carriers are strongly coupled to magnetic fluctuations.

We present an analytical formalism investigating effects of multiple excitations with different dispersion parameters in the context of neutron resonance spin echo spectroscopy. This allows identifying conditions to obtain high-resolution information on the energy split of two dispersive modes which may differ or not in their local energy gradient. Comparison to experimental data is provided by recent measurements on magnon excitations in RbMnF3. Potential future applications are investigations of hybridized phonon or magnon modes or mixed excitations. peerReviewed

The pseudogap phenomenon, a discontinuity in the energy level of a material's electronic spectrum, is a universal characteristic of the high transition temperature (Tc) copper oxides. The nature of the pseudogap has been a central question in condensed matter physics for more than a decade, but many of its properties remain unexplained. Recent studies have pointed to the universal existence of an unusual magnetic order below T*, the temperature below which the anomalous properties associated with the pseudogap become apparent. If confirmed, this would have the profound implication that the pseudogap regime constitutes a genuine new phase of matter rather than a mere crossover phenomenon. The results of inelastic neutron scattering experiments on the superconductor HgBa2CuO4+δ (Hg1201) now reveal a fundamental collective magnetic mode associated with the unusual order, providing further support for this picture. Recent findings indicate that the pseudogap regime in the high-transition-temperature copper oxides constitutes a new phase of matter rather than a mere crossover phenomenon. These authors report inelastic neutron scattering results for HgBa2CuO4+δ that reveal a fundamental collective magnetic mode associated with the unusual order, further supporting this picture. The mode's intensity rises below the pseudogap characteristic temperature and its dispersion is weak. The elucidation of the pseudogap phenomenon of the high-transition-temperature (high-Tc) copper oxides—a set of anomalous physical properties below the characteristic temperature T* and above Tc—has been a major challenge in condensed matter physics for the past two decades1. Following initial indications of broken time-reversal symmetry in photoemission experiments2, recent polarized neutron diffraction work demonstrated the universal existence of an unusual magnetic order below T* (refs 3, 4). These findings have the profound implication that the pseudogap regime constitutes a genuine new phase of matter rather than a mere crossover phenomenon. They are furthermore consistent with a particular type of order involving circulating orbital currents, and with the notion that the phase diagram is controlled by a quantum critical point5. Here we report inelastic neutron scattering results for HgBa2CuO4+δ that reveal a fundamental collective magnetic mode associated with the unusual order, and which further support this picture. The mode’s intensity rises below the same temperature T* and its dispersion is weak, as expected for an Ising-like order parameter6. Its energy of 52–56 meV renders it a new candidate for the hitherto unexplained ubiquitous electron–boson coupling features observed in spectroscopic studies7,8,9,10.

YBa2Cu3Ox thin films were deposited by sputtering on (1102) sapphire and (100) silicon using an intermediate buffer layer of Y-stabilized ZrO2 (YSZ). On sapphire the YSZ layer and the YBa2Cu3Ox grew epitaxially as was confirmed by ion channeling and RBS. The c-oriented YBa2Cu3Ox films had a Tc of up to 90 K and jc was 0.5−1.4 ∗ 106 A/cm2 at 77 K in zero magnetic field. On silicon the YSZ and the YBa2Cu3Ox layer were highly textured, but polycrystalline. These YBa2Cu3Ox films had Tc values of up to 79 K.

We show that the superconducting energy gap $\Delta$ can be directly observed in phonon spectra, as predicted by recent theories. In addition, since each phonon probes the gap on only a small part of the Fermi surface, the gap anisotropy can be studied in detail. Our neutron scattering investigation of the anisotropic conventional superconductor YNi$_2$B$_2$C demonstrates this new application of phonon spectroscopy., Comment: 4 pages, 5 figures

The magnetism of charge-stripe-ordered ${\text{La}}_{1.55}{\text{Sr}}_{0.45}{\text{NiO}}_{4}$ was studied by a combination of neutron diffraction, muon-spin relaxation $(\ensuremath{\mu}\text{SR})$, and bulk susceptibility. Long-range magnetic ordering was observed at a lower temperature by $\ensuremath{\mu}\text{SR}$ than by neutron diffraction, consistent with a glassy transition to the ordered phase. A second magnetic transition is detected by all techniques and is consistent with a spin reorientation. On cooling below ${T}_{\text{SR}}=42\text{ }\text{K}$ the spins reorientate from lying $32.9\ifmmode\pm\else\textpm\fi{}0.6\ifmmode^\circ\else\textdegree\fi{}$ away from the stripe direction at 70 K to $56.8\ifmmode\pm\else\textpm\fi{}0.4\ifmmode^\circ\else\textdegree\fi{}$ at 10 K. The magnetic order was observed by neutron diffraction to have both three-dimensional and two-dimensional (without any correlation along the $c$ axis) characters. $\ensuremath{\mu}\text{SR}$ measurements confirmed this and are consistent with a single magnetically ordered spin-stripe phase. The effects of checkerboard charge order on the ordered phase and the characteristics of the phase diagram of the spin reorientation in charge-ordered ${\text{La}}_{2\ensuremath{-}x}{\text{Sr}}_{x}{\text{NiO}}_{4}$ are commented on.

We report a neutron scattering study of the spin excitation spectrum in the superconducting state of the slightly overdoped ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ system $({T}_{c}=87\phantom{\rule{0.3em}{0ex}}\mathrm{K})$. We focus on the dispersion of the resonance peak in the superconducting state that is due to a $S=1$ collective mode. The measured spin excitation spectrum bears a strong similarity to the spectrum of the ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+x}$ system for a similar doping level (i.e., $x\ensuremath{\sim}0.95\ensuremath{-}1$), which can be described as intersecting upward- and downward-dispersing branches. A close comparison of the threshold of the electron-hole spin flip continuum, known from angle resolved photoemission measurements in the same system, indicates that the magnetic response in the superconducting state is confined, in both energy and momentum, below the gapped Stoner continuum. In contrast to ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+x}$, the spin excitation spectrum is broader than the experimental resolution. In the framework of an itinerant-electron model, we quantitatively relate this intrinsic energy width to the superconducting gap distribution observed in scanning tunneling microscopy experiments. Our study further suggests a significant in-plane anisotropy of the magnetic response.