Evidence for Jahn-Teller Distortions at the Antiferromagnetic Transition inLaTiO3

Abstract

LaTiO3 is known as a Mott insulator which orders antiferromagnetically at T(N)=146 K. We report on results of thermal expansion and temperature dependent x-ray diffraction together with measurements of the heat capacity, electrical transport measurements, and optical spectroscopy in untwinned single crystals. At T(N) significant structural changes appear, which are volume conserving. Concomitant anomalies are also observed in the dc resistivity, in bulk modulus, and optical reflectivity spectra. We interpret these experimental observations as evidence of orbital order.

Temperature dependence of the electronic structure of theJeff=12Mott insulatorMoon1, Jin2, Choi3 et al. 2009Phys. Rev. B157251005View full textAdd to dashboardCite

“…In particular, we note that LaTiO 3 showed a structural transition at its magnetic transition temperature. Structural studies using x-ray and neutron diffraction techniques indicated a structural transition near the magnetic transition temperature, 22,23 and an optical study on LaTiO 3 showed that the additional phonon modes appeared below the magnetic transition temperature due to the structural transition. 19 However, the electronic structure and Mott gap of LaTiO 3 hardly changed with temperature.…”

Phonons and magnetic excitations in the Mott insulatorLaTiO3

“…, where large background and Fano shape of the phonon line near 300 cm −1 have been observed, may also indicate orbital fluctuations coupled to lattice vibrations. Some recent experimental results on the temperature dependence near T N of neutron and x-ray diffraction, heat capacity and infrared spectra [4,5], however, provide evidence for noticeable deformation of TiO 6 octahedra and structural anomaly near the antiferromagnetic ordering, which indirectly supports the concept of orbital ordering.The observation in the Raman spectrum of insulating rare earth titanates of structureless background and Fano interference is highly unusual. At the same time, it is well known that transport and magnetic properties of LaTiO 3 [7,8,9] depend crucially on sample's stoichiometry.…”

Magnetoelastic coupling inRTiO3(R=La,NdKomarek1, Roth2, Cwik3 et al. 2007Phys. Rev. B128111540View full textAdd to dashboardCite

“…Pavarini et al 23 argue that the values of the tilting and the concomitant shift of the RE sites would determine the splitting of the orbital levels 23 . However, the lattice parameters and the octahedron deformation in LaTiO 3 exhibit clear anomalies around the magnetic ordering suggesting that there is an intrinsic coupling between orbital degrees of freedom and the crystal structure 5,35 . It is the aim of the present work to further elucidate this orbital-lattice coupling in the RETiO 3 series and to separate the intrinsically electronic effects from tilt and rotation distortions.…”