by single-crystal neutron diffuse scattering*

The Jahn-Teller (JT) distortion occurs in a single valance system where a structural distortion is needed to lift the orbital degeneracy. In the mixed valance system La_1-xSr_xMnO₃ (LSMO), the JT transition remains robust and sharp. It is not clear if the distribution of Mn³⁺ in Mn⁴⁺ matrix plays an important role. On cooling, LSMO undergoes the cooperative JT transition to order orbitals, spin ordering transition, and the charge ordering transition[1]. Pair distribution function analysis of neutron powder diffraction data has previously been done to discuss the role of polarons in the transition[2,3]. With single-crystal neutron diffuse scattering (NDS), we have observed patterns that show an interesting evolution as it is cooled through three transitions. Weak rod-shaped NDS features along L with even H+K above T_JT get enhanced as the temperature is cooled below T_JT, suggesting coherent scattering is developed above T_JT. The NDS features disappear below the charge ordering transition temperature T_CO, associated with the formation of superlattices. Potential models to interpret the observations will be discussed.
[1] Phys. Rev. B 91, 064414 (2015)
[2] Phys. Rev. Lett. 77, 715 (1996)
[3] Phys. Rev. B 56, R8475 (1997)