Scattering of 64 eV to 3 keV neutrons from polyethylene and graphite and the coherence length problem

We measured the neutron scattering intensity ratios from polyethylene (CH2) relative to graphite (C) at several discrete final energies, of narrow widths (approximately 3 eV) between 64 eV and 3 keV. The final energies were selected using a 238U filter. This experiment was carried out to search for any anomaly in the n-p scattered intensities from CH2 caused by the neutron coherence length. The scattered intensity ratios were found to conform to conventional expectations and no anomaly was observed.     

Pressure-induced phase transition in Sb2Te3

An anomalous change in electrical resistance with pressure was observed in crystalline Sb₂Te₃ around 80 kbar at room temperature. This anomaly was found to be closely related with a pressure-induced structural phase transition which is discovered by the present x-ray diffraction experiment.     

Observation of anomalous phonon softening in bilayer graphene

The interaction of electron-hole pairs with lattice vibrations exhibits a wealth of intriguing physical phenomena such as the renowned Kohn anomaly. Here we report the observation in bilayer graphene of an unusual phonon softening that provides the first experimental proof for another type of phonon anomaly. Similar to the Kohn anomaly, which is a logarithmic singularity in the phonon group velocity [W. Kohn, Phys. Rev. Lett. 2, 393 (1959)], the observed phonon anomaly exhibits a logarithmic singularity in the optical-phonon energy. Arising from a resonant electron-phonon coupling effect, the anomaly was also expected, albeit not observed, in monolayer graphene. We propose an explanation for why it is easier to observe in bilayer samples.     

Combined Study of Structural,Magnetic and Transport Properties of Eu_(0.5)Ln_(0.5)BiS_2F Superconductor

Superconductivity below 0.3 K and a charge-density-wave-like(CDW-like) anomaly at 280 K were observed in EuBiS_2F recently.Here we report a systematic study of structural and transport properties in Eu_(0.5)Ln_(0.5)BiS_2F(Ln=La,Ce,Pr,Nd,Sm) by electrical resistivity,magnetization,and specific heat measurements.The lattice constants have a significant change upon rare earth substitution for Eu,suggesting an effective doping.As Ln is changed from Sm to La,the superconducting transition temperature T_c increases from 1.55 K to 2.8 K.In contrast to the metallic parent compound,the temperature dependence of electrical resistivity displays semiconductinglike behavior for all the Eu_(0.5)Ln_(0.5)BiS_2F samples.Meanwhile,the CDW-like anomaly observed in EuBiS2F is completely suppressed.Unlike the mixed valence state in the undoped compound,Eu ions in these rareearth-doped samples are mainly divalent.A specific anomaly at 1.3 K resembling that in EuBiS2F suggests the coexistence of superconductivity and spin glass state for Eu_(0.5)La_(0.5)BiS_2F.Coexistence of ferromagnetic order and superconductivity is found below 2.2 K in Eu_(0.5)Ce_(0.5)BiS_2F samples.Our results supplies a rich diagram showing that many interesting properties can be induced in BiS_2-based compounds.     

(Pr,Nd)_(2/3)Sr_(1/3)MnO_3体系中的低温比热反常现象

主要研究了(Pr1-yNdy)2/3Sr1/3MnO3体系多晶样品在低温下的比热反常现象.Pr2/3Sr1/3MnO3在低温下没有比热反常现象,但随着Nd替代Pr,比热反常开始出现,峰值逐渐增加,峰值出现温度逐渐减小;在磁场的作用下,峰值减小,峰值出现温度逐渐增加;经分析,该低温比热反常现象与Schottky效应相关.     

Neutron scattering study of the phase transitions in a doped polycrystalline Fe3O4: Zn0.005Fe2.995O4

Temperature dependent neutron elastic scattering and resistivity measurements have been made on a polycrystalline sample of Zn_0.005Fe_2.995O₄, which displayed a well-separated, bifurcated, heat-capacity anomaly. The lower-temperature anomaly (near 110 K) was found to be associated with a lattice distortion, but no change in neutron intensity was observed at the higher-temperature anomaly (near 119 K). The electrical resistivity of this sample also exhibited an abrupt change only at the lower-temperature anomaly. The downward shift of the lower-temperature, λ-type anomaly as a result of the very low Zn impurity is, however, confirmed by the neutron scattering results and demonstrates the extreme sensitivity of the structural transition to impurities.     

Anomalous behavior of the absorption tail due to a phase transition in Sb2S3

Absorption spectra near the fundamental absorption edge in Sb₂S₃ are studied between 77 and 380 K. It is found that the absorption tail obeys the Urbach rule between 130 and 230 K, while an anomaly associated with the second-order diffuse phase transition is observed above 230 K.     

The specific heat of potassium holmium double tungstate

The results of measurements of thermal properties (specific heat) of potassium holmium double tungstate KHo(WO₄)₂ as a function of temperature (from 0.5 to 300?K) and magnetic field (up to 2?T) are presented. The total specific heat without the phonon and Schottky contributions is found to have the anomaly with maximum at T _SPT?～?5?K. This anomaly is likely related with the structural phase transition (SPT) caused by the cooperative Jahn–Teller effect. The increase of specific heat at very low temperatures and its shift towards high temperatures with increasing magnetic field are observed. The origin of this behaviour can be connected with possible magnetic phase transition induced by magnetic field.     

Search for anomalous scattering of keV neutrons from H2O-D2O mixtures

We measured the neutron scattering intensities from pure liquid H2O relative to that of pure D2O and also relative to H2O-D2O mixtures, at room temperature. This study is relevant to the problem of quantum entanglement. The neutrons were generated from an electron Linac and the final energy of the scattered neutrons was fixed at 24.3 keV using a 20 cm thick pure iron filter. The scattering intensity ratios were found to agree with expected values deduced from the tabulated total cross sections within an accuracy of 3%. Thus no anomaly was observed.     

Experimental verification of the early crisis of drag using a single sphere

The recently discovered phenomenon of drag anomaly (early crisis) observed for droplets in a two-phase turbulent flow at transition Reynolds numbers (Re = 10–100) is experimentally supported in the case of a gas flow about a single hard sphere as well. Using a specially designed torsion balance, the drag force of a foam plastic sphere 3 mm in diameter placed in a blower-produced turbulent jet is measured. It is found that the turbulence of the flow about the sphere must be high for the drag anomaly to arise.     

Electrical and magnetic properties of pseudo-one-dimensional calcium iridium oxide Ca5Ir3O12

The electrical and magnetic properties of one-dimensional calcium iridium oxide Ca₅Ir₃O₁₂ are investigated. A weak ferromagnetic transition has been found at 7.5 K through magnetic susceptibility measurements. At the same temperature, a λ-type specific heat anomaly has been observed. The effective magnetic moments in the paramagnetic temperature range and the magnetic entropy due to the magnetic transition indicates that the tetravalent and pentavalent Ir ions exist in the ratio of 1:2. Another λ-type anomaly has been observed at 105 K in the temperature dependence of the specific heat. The electrical conductivity shows one-dimensional Mott variable-range hopping conduction behavior.     

Possible antiferromagnetic ordering in Y2Cu2O5. Paramagnetic behaviour of BaCuO2

The susceptibility anomaly observed at 13 K for Y₂Cu₂O₅ strongly suggests the occurrence of antiferromagnetic Cu spin coupling in this compound. Only paramagnetic behaviour was found for BaCuO₂.     

The role of iron ions on the structure and certain physical properties of PbO-As2O3 glasses

Various studies have been carried out viz optical absorption, infrared spectra, magnetic susceptibility, dielectric parameters (dielectric constant, loss and a.c. conductivity over a range of frequency and temperature; and breakdown strength) and differential thermal analysis of PbO-As₂O₃ glasses containing 0-1 mol% of Fe₂O₃. An anomaly has been observed in all the properties of these glasses when Fe₂O₃ concentration is about 0.25 mol%. The reasons for such anomaly have been identified and found that PbO-As₂O₃ glasses are more stable when Fe₂O₃ concentration is about 0.25 mol%.     

Connection between the low temperature anomaly in glasses and the glass transition temperature

The low temperature specific heat anomaly in water-doped K-Ca nitrate glass has been found to scale with the reciprocal glass transition temperature. Similarly, the anomaly in Na₂O-containing and in neutron-irradiated silica scales with the reciprocal fictive temperature. These observations lead to the suggestion that the frozen-in disorder is connected with the low temperature anomaly characteristic of the glassy state.     

Anomalous behaviour of KC1 : OH− crystals' low temperature specific-heat

An anomaly of KC1 crystals specific-heat doped with hydroxyl was observed in the temperature range 5–30°K. The found specific-heat excess is well described in terms of a formula for substitution impurity with 32 cm^?1 quasi-local level coinciding with the frequency observed in infrared absorption.     

The aetiology of sigma model anomalies

Certain nonlinear sigma models with fermions are ill-defined due to an anomaly which exhibits characteristics of both the nonabelian gauge theory anomaly and the SU(2) anomaly. The simplest way to diagnose the anomaly involves consideration of the global topology of the theory. We review the mathematical methods needed for this analysis and apply them to several supersymmetric sigma models. Some of these are found to be anomalous.     

Crisis of hydrodynamic drag of drops in the two-phase turbulent flow of a spray produced by a mechanical nozzle at transition reynolds Numbers

When processing experimental data for the hydrodynamics of a two-phase flow in a spray produced by a mechanical nozzle, we revealed an anomaly in the behavior of the hydrodynamic drag of drops: the drag coefficient turns out to be four to seven times lower than the previously known values. Several hypotheses are put forward to explain the anomaly. It is found that, when the gas flows around drops under highly turbulent conditions, an “early” (i.e., observed even at transition Reynolds numbers, Re>50) crisis of drag resistance of drops takes place. This new physical phenomenon allows us to account for a number of features of the two-phase flow that are observed in the experiment. Among these features is, in particular, the fact that the momentum transferred to the gas is roughly half the initial momentum of the liquid jet.     

Magnetic hyperfine anomaly in muonic193Ir

The nuclear decay of the 5/2⁺ 139 keV state to the 3/2⁺ ground state was observed in muonic¹⁹³Ir. The hyperfine splitting of the 3/2⁺ state and 5/2⁺ state was determined to be 640±100 eV and 1280±160 eV, respectively. The ground state splitting is about twice that of a point nucleus, an anomaly never observed this large. This is mainly due to the different radial distribution of spin and orbital magnetization of a d_3/2 proton configuration for which these contributions nearly cancel to zero in the magnetic moment. But calculations including configuration mixing and coupling to a vibrating or a deformed core show deviations. The groundstate anomaly is in line with that observed by the Mössbauer technique.     

Superconductivity in Hole-Doped （S1-xKx）Fe2As2

A series of layered （Sr1-xKx）Fe2As2 compounds with nominal x = 0-0.40 are synthesized by solid state reaction method. Similar to other parent compounds of iron-based pnictide superconductors, pure SrFe2As2 shows a strong resistivity anomaly near 210 K, which was ascribed to the spin-density-wave instability. The anomaly temperature is much higher than those observed in LaOFeAs and BaFe2As2, the two prototype parent compounds with ZrCuSiAs- and ThCr2Si2-type structures. K-doping strongly suppresses this anomaly and induces superconductivity. Like in the case of K-doped BaFe2As2, sharp superconducting transitions at Tc ～ 38 K is observed. We perform the Hall coefficient measurement, and confirm that the dominant carriers are hole-type. The carrier density is enhanced by a factor of 3 in comparison to F-doped LaOFeAs superconductor.     

Invar effects in Zr0.7Nb0.3Fe2

A thermal expansion anomaly similar to that of the invar alloy was observed in a Laves phase intermetallic compound, Zr_0.7Nb_0.3Fe₂. This anomaly is explained as a result of a large spontaneous volume magnetostriction. Magnetic properties and magnetovolume effects of this material are discussed on the basis of the band of ferromagnetism.