Professor Stephen Blundell

Abstract:

The muon spin rotation (mu SR) technique is primarily a powerful probe of the magnetic properties of materials; but it is also possible to measure charge-density related effects using muon quadrupolar level crossing resonance (QLCR). We present the first study of a charge density wave (CDW) using mu SR in TTF-TCNQ. The CDW develops below the metal-insulator transition at 54 K and we study the evolution of the CDW as a function of temperature using the QLCR resonances of the nitrogen atoms on the TCNQ molecules as the probe.

Abstract:

We present a model of a quasi-one-dimensional (Q1D) conductor with weak dispersion in the direction perpendicular to the chains in a magnetic field. Finite-energy electric dipole transitions between the eigenstates of the system constitute Fermi-surface traversal resonance, a Q1D analogue of cyclotron resonance. We extend the model to describe a (TMTSF)(2)X-like material, with dispersion in two directions perpendicular to the chains, and find that for certain orientations of the magnetic field large degeneracies occur between the magnetic-field induced states. These are angles at which maxima are observed experimentally in the d.c. conductivity, and thus we explain one class of angle-dependent magnetoresistance oscillations (AMRO) in terms of zero-energy electric dipole transitions between magnetic-field induced states.