X-ray and neutron scattering

Abstract:

The origin of colossal magnetoresistance (CMR) in manganese oxides is among the most challenging problems in condensed-matter physics today. The true nature of the low-temperature electronic phase of these materials is heavily debated. By combining photoemission and tunnelling data, we show that in the archetypal bilayer system La 2-2x Sr 1+2x Mn 2 O 7 , polaronic degrees of freedom win out across the CMR region of the phase diagram. This means that the generic ground state of bilayer manganites supports a vanishing coherent quasi-particle spectral weight at the Fermi level throughout k-space. The incoherence of the charge carriers, resulting from strong electron-lattice interactions and the accompanying orbital physics, offers a unifying explanation for the anomalous charge-carrier dynamics seen in transport, optics and electron spectroscopies. The stacking number N is the key factor for true metallic behaviour, as an intergrowth-driven breakdown of the polaronic domination to give a metal possessing a traditional Fermi surface is seen in this system.

Abstract:

Magneto-electric multiferroics exemplified by TbMnO(3) possess both magnetic and ferroelectric long-range order. The magnetic order is mostly understood, whereas the nature of the ferroelectricity has remained more elusive. Competing models proposed to explain the ferroelectricity are associated respectively with charge transfer and ionic displacements. Exploiting the magneto-electric coupling, we used an electric field to produce a single magnetic domain state, and a magnetic field to induce ionic displacements. Under these conditions, interference between charge and magnetic x-ray scattering arose, encoding the amplitude and phase of the displacements. When combined with a theoretical analysis, our data allow us to resolve the ionic displacements at the femtoscale, and show that such displacements make a substantial contribution to the zero-field ferroelectric moment.

Abstract:

Magneto-electric multiferroics exemplified by TbMnO 3 possess both magnetic and ferroelectric long-range order. The magnetic order is mostly understood, whereas the nature of the ferroelectricity has remained more elusive. Competing models proposed to explain the ferroelectricity are associated respectively with charge transfer and ionic displacements. Exploiting the magneto-electric coupling, we used an electric field to produce a single magnetic domain state, and a magnetic field to induce ionic displacements. Under these conditions, interference between charge and magnetic x-ray scattering arose, encoding the amplitude and phase of the displacements. When combined with a theoretical analysis, our data allow us to resolve the ionic displacements at the femtoscale, and show that such displacements make a substantial contribution to the zero-field ferroelectric moment.

Abstract:

TOF experiments were carried out at room temperature and high temperature for Zr rich PbZr1-xTixO3 powders. The best R-factors were obtained with a mixture of R3c and Cm phases. The composition of the Cm phase monotonically increases towards the MPB. At high temperature in the cubic phase, the ADPs for the Pb atom become smaller when Pb displacements along either >110111

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