A.D. Taylor

Local structural instability of high-T c oxide superconductors studied by inelastic neutron scattering

The scattering function,S(Q, E), of superconducting La1.85Sr0.15CuO4 and YBa2Cu3O7 was measured over a wide range ofQ-E space by inelastic neutron scattering. Fine structures in their phonon density of states as well as theQ-dependences ofS(Q, E) were observed. TheQ-dependence ofS(Q, E) is very susceptive atTc, with an anomalous behavior similar to a critical phenomenon. We have found that the anomalous behavior is related to the local structural instability, i.e., the 〈110〉 buckling motion of the Cu-O plane and the shortening of the distance between the apical oxygen and the copper atom in the plane.

High energy magnetic neutron scattering in heavy fermion compounds

Abstract High energy magnetic inelastic neutron scattering measurements of intermultiplet transitions in rare earth and actinide metals have established the importance of intra-atomic correlations even in the presence of strong hybridisation. Well-defined transitions are observed up to an energy of 1766 meV in thulium metal. The 3H4→3F2 transition is observed across the alloy series U(Pd1−xPtx)3, showing that localized 5f2 excitations persist in the heavy fermion compound UPt3. The splitting of the spin-orbit transition in CeAl3 suggests that hybridisation is an important component in the crystal field potential.

Neutron spectroscopy of the crystalline electric field in high-Tc YbBa2Cu3O7

Abstract Inelastic neutron scattering has been employed to study the crystalline electric field (CEF) interaction in the high-T c superconductor YbBa 2 Cu 3 O 7 . The observed energy spectra exhibit three well defined CEF transitions at 88.5, 92.8 and 98.5 meV which completely determine the CEF splitting of the ground-state J-multiplet. A set of CEF parameters is derived which excellently reproduce the neutron spectroscopic data as well as the thermodynamic magnetic properties.

Neutron spectroscopic studies of crystalline electric fields in high-Tc ErBa2Cu3O7 doped with zn and Ni

Abstract The crystalline electric field (CEF) splitting of the ER 3+ 4f-shell in the high- T c superconductor ErBa 2 Cu 3 O 7 doped with Zn and Ni has been investigated by the inelastic neutron scattering tecnique. the observed exhibit a large number of well resolved CEF transitions between 8 and 80 meV, so that we have been able to determine all nine CEF parameters required for the orthorhombic symmetry. The results are used to derive information on the effective charge associated with the superconducting CuO 2 planes.

Magnetic properties of Nd3+ in Nd−Ba−Cu−O-compounds

Neutron diffraction, neutron spectroscopy and magnetization measurements have been employed to study the structural, electronic, and magnetic behavior of eleven compounds with the general formula Nd1+yCavBa2−y−vCu3Ox (0≦y≦0.5; 0≦v≦0.25; 6≦x≦7). The structure turned out to react to oxygen reduction similar as other 123-compounds, yielding discontinuities close to the metal-insulator-transition and the well-known relations of bond lengths as a function ofTc. The crystalline electric field (CEF) interaction, splitting the 10-fold degenerate ground-state J-multiplet of the Nd3+-ions into five doublet states, was investigated by neutron spectroscopy. The derived CEF parameters have been used to determine changes in the electronic surroundings of the Nd3+ ions. In addition, with the help of the CEF parameters the thermodynamic magnetic properties of these compounds were calculated which turn out to be in good agreement with the experimental data.

Crystal field excitations in ErMn4Al8

Abstract Distinct crystal field excitations have been observed in tetragonal ErMn4Al8 by inelastic neutron scattering. The energy level sequence and crystal field parameters have been obtained from the observed crystal field transition peak positions and intensities. The crystal field parameters account for the basal plane orientation of the Er magnetic moment in ErFe4Al8 and if extrapolated to the Fe rich compounds ErFe11Ti and ErFe10V2 also can account for the observed planar anisotropy.

Inelastic neutron scattering in liquid lithium

Abstract We have measured the dynamic structure factor in liquid 7 Li at 473 K with the time-of-flight spectrometer MARI at the spallation neutron source ISIS with incident energies of 25 and 525 meV. We give preliminary results and we investigate the hydrodynamic limit as well as the approach to the impulse approximation.

Anomalous crystal field splitting in YbN

Abstract The anomalous splitting of the λ 8 excited state of YbN was studied by neutron inelastic scattering. The experimental result suggests that the anomaly arises from the magneto-elastic interaction.

Phonon density of states of super- and non-superconducting states in La1.85Sr0.15Cu1-xZnxO4 (x=0, 0.02)

Abstract Inelastic neutron scattering measurements have been performed on superconducting La 1.85 Sr 0.15 CuO 4 ( T c =38 K ) and non-superconductin g La 1.85 Sr 0.15 Cu 0.98 Zn 0.02 O 4 ( T c K ). We observedc a small but systematic difference in the phonon density of states (PDOS) between the superconducting and the normal state of these samples. This reference in the PDOS mainly corresponds to a change of the Cu-O bond stretching mode in the CuO 2 plane. The temperature variation of the PDOS of La 1.85 Sr 0.15 CuO 4 below ( T =20 K ) T c and above ( T =50 K ) T c approximately corresponds to the change induced by the Zn-doping. The possible interpretation of the difference in the vibrational states between the two phases is discussed in terms of electron-phonon coupling and an anomalous local structure change.

A second target station for ISIS

Abstract The ISIS Facility has demonstrated that accelerator-driven pulsed spallation sources can compete successfully with the worlds most advanced conventional neutron scattering facilities and indeed expand the frontiers of neutron scattering into new regimes. A second target station at ISIS – specifically optimised for long wavelengths and high resolution studies – will impact on studies of complex systems including surfaces and interfaces, large-scale structures and problems in biology and biotechnology.