NEUTRON AND X-RAY SCATTERING STUDIES OF THE SPIN-PEIERLS TRANSITION IN CuGeO₃ Kazuma Hirota, Physics Department, Tohoku University, Sendai 980-77, Japan

In 1993, Hase et al.¹ reported that an inorganic linear Cu²⁺ (S = 1/2) chain compound CuGeO₃ undergoes a spin-Peierls (SP) transition, which had been previously known only in several organic compounds. Since this simple inorganic oxide gives us the first chance to fully understand the detailed mechanism of this phase transition into a singlet state, it is not surprising that CuGeO₃ has attracted much attention from researchers in a variety of fields. Among many kinds of measurements, neutron and x-ray scattering techniques and their combination have been playing a central and significant role in its research, and in fact found two most crucial evidences of an SP transition, i.e., the singlet-triplet excitation² and the dimerization along the chain³. CuGeO₃ is, however, significantly different from organic SP compounds in two aspects, which are the lack of a good one-dimensionality in the magnetism (J_c : J_b : J_a ~ 1 : 0.1 : 0.01) [2] as well as no obvious phonon softening at the dimerization q vector (1/2, 1, 1/2)⁴. Both of them had been considered necessary conditions for an SP transition in the course of studying organic systems. We will discuss recent neutron and x-ray scattering experiments with referring to a possible mechanism which realizes the SP transition in CuGeO₃.

¹M. Hase et al., Phys. Rev. Lett. 70, 3651 (1993)

²M. Nishi et al., Phys. Rev. B 50, 6508 (1994)

³K. Hirota et al., Phys. Rev. Lett. 73, 736 (1995)

⁴K. Hirota et al., Phys. Rev. B 52, 15412 (1995)