Hamburg 2001 – scientific programme

Parts | Days | Selection | Search | Downloads | Help

TT: Tiefe Temperaturen

TT 17: Korrelierte Elektronensysteme Theorie II

TT 17.4: Talk

Wednesday, March 28, 2001, 17:00–17:15, H

Spin Dynamics and Orbital State in LaTiO₃ and YTiO₃ — •C. Ulrich¹, H. He¹, G. Khaliullin¹, J.W. Lynn², A. Ivanov³, M. Ohl^3,4, Y. Taguchi⁵, Y. Tokura⁵, and B. Keimer¹ — ¹Max-Planck-Institut FKF, Stuttgart, Germany — ²NIST, Center for Neutron Research, Gaithersburg, U.S.A. — ³Institut Laue-Langevin, Grenoble, France — ⁴Forschungszentrum Jülich, Germany — ⁵University of Tokyo, Japan

Transition metal oxides with the perovskite structure display a large variety of unusual properties such as high temperature superconductivity or colossal magnetoresistance. While LaTiO₃ is an antiferromagnetic 3d¹ Mott-Hubbard insulator, YTiO₃ shows ferromagnetic ordering at low temperature. We have studied the spin wave dispersion relations of LaTiO₃ and YTiO₃ by inelastic neutron scattering. It has turned out, that the orbital degrees of freedom give rise to fascinating physics in the titanates. The almost complete isotropic spin wave spectrum we measured in LaTiO₃ is inconsistent with a conventional scenario in which the orbital degrees of freedom order at high temperature and lock in the exchange interactions according to which the system orders magnetically at low temperatures. Rather, the data point towards an unusual ground state with strong orbital quantum fluctuations even at T = 0 K. The spin wave spectrum of YTiO₃ on the other hand shows that it is a ferromagnetic orbitally ordered system. The microscopic origin of these disparate ground states will be discussed, and the data on the titanates will be compared to analogous data on the 3d² systems LaVO₃ and YVO₃.