Professor Stephen Blundell

Abstract:

We present the first muon spin rotation/relaxation study of a nematic liquid crystal (5CB). We identify four different positions for muonium addition to this compound by correlating the dominant peaks in the Fourier transform of the muon precession signal obtained in an applied transverse magnetic field. Experiments performed in a longitudinal field are used to probe changes in individual molecular dynamics at the solid-nematic transition. High field avoided level crossing spectroscopy reveals four ΔM=0 transitions which can be fitted using simplified models of collective molecular dynamics appropriate to the solid, nematic, and liquid phases. © 2001 The American Physical Society.

Abstract:

We present the first muon spin rotation/relaxation study of a nematic liquid crystal (5CB). We identify four different positions for muonium addition to this compound by correlating the dominant peaks in the Fourier transform of the muon precession signal obtained in an applied transverse magnetic field. Experiments performed in a longitudinal field are used to probe changes in individual molecular dynamics at the solid-nematic transition. High field avoided level crossing spectroscopy reveals four ΔM=0 transitions which can be fitted using simplified models of collective molecular dynamics appropriate to the solid, nematic, and liquid phases.

Abstract:

An angle-dependent study of the magneto-optical response of the p-wave triplet-paired perovskite superconductor Sr2RuO4\ reveals several new cyclotron resonance effects. We observe an odd-harmonic cyclotron resonance series, probably arising from the gamma Fermi surface, with a fundamental cyclotron mass of 12.6 m(e). In addition, we find several resonance branches which behave in unconventional ways owing to the unusual nature of the band dispersion in this material. The results confirm the complexity of the Sr2RuO4 Fermi surface topology and show that earlier conclusions drawn from millimetre-wave experiments should be reconsidered. (C) 2001 Elsevier Science B.V. All rights reserved.

Abstract:

Traditional solid state synthetic methods were used to prepare a polycrystalline sample of the n = 3 Ruddlesden-Popper phase Ca4Mn2TiO9.93. The crystal structure (space group Pbca, a = 5.31411(5), b = 5.31148(5), c = 26.9138(2)Angstrom) was determined by the simultaneous analysis of neutron and X-ray diffraction data, with near-edge anomalous scattering being used to provide contrast between Mn and Ti cations. The latter show a small preference for the octahedral sites at the centre of the three-layer perovskite blocks within the structure. Neutron diffraction data collected at 5 K show no evidence for long-range magnetic ordering, although an enhanced magnetisation with a weak remanence is observed at low temperature; this is ascribed to the presence of antisymmetric exchange interactions. Ca4Mn2TiO9.93 is a semiconductor with a temperature-dependent activation energy of similar to 100 meV. Only weak (rho (B)/rho (0) > 0.9 in 14 T at 75 K) magnetoresistance was observed.