ISSP - The institute for Solid State Physics

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Yoshizawa Group
Professor
YOSHIZAWA,
Hideki

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Metal-insulator transition in transition-metal oxides has drawn much attention because such a phenomenon reflects interplay among spin, charge, lattice, and orbital degrees of freedom. Our group has been studying their behavior by neutron scattering technique with use of pulse and steady-source neutron beams, and the triple axis neutron spectrometer owned by the ISSP is shown in the left bottom figure. The hole-doping dependences of the incommensurability and the transition temperature of the stripe ordering for hole concentration x up to x = 0.5 have been observed in the highly-doped La2-xSrxNiO4 which is one of the isomorphic compounds of the High Tc cuprate superconductors. The ordering temperatures of the stripe charge as well as spin orderings have the maxima at x = 1/3, and they decrease beyond x = 1/3. Beyond x = 1/2, the Ni system gradually becomes metallic and show the insulator to metal transition at x ~ 0.9. Our recent pulse neutron studies on the Ni system revealed that the characteristics of the spin dynamics changes at x = 0.5, and further detail studies of such unusual spin dynamics and their relation to the transport properties are now ongoing.

Triple-axis spectrometer installed at the JRR-3 in the Japan Atomic Energy Agency, Tokai, Ibaraki.
Doping dependence of the stripe ordering in highly-doped La2-xSrxNiO4, which is an isomorphic compounds of one of High Tc cuprate superconductors La2-xSrxCuO4. Unlike the expectation from the previous studies, the transition temperatures of the stripe charge and spin orderings exhibit the maximums at x = 1/3, and decreases above x = 1/3. The periodicity of the stripe order is approximately linear in x, but levels off beyond x = 1/2. The system gradually becomes metallic and shows the insulator to metal transition near x ~ 0.9.

Research Subjects

  1. Neutron scattering study of metal-insulator transition, magnetic ordering, charge/orbital orderings in transition-metal oxides
  2. Neutron scattering study of spin sturucture and dynamics in noncentrosymmetric magnetic superconductors