Dielectric properties and dynamical conductivity ofLaTiO3: From dc to optical frequencies

Abstract

We provide a complete and detailed characterization of the temperature-dependent response to ac electrical fields of LaTiO 3 , a Mott-Hubbard insulator close to the metal-insulator transition. We present combined dc, broadband dielectric, mm-wave, and infrared spectra of ac conductivity and dielectric constant, covering an overall frequency range of 17 decades. The dc and dielectric measurements reveal information on the semiconducting charge-transport properties of LaTiO 3 , indicating the importance of Anderson localization, and on the dielectric response due to ionic polarization. In the infrared region, the temperature dependence of the phonon modes gives strong hints for a structural phase transition at the magnetic ordering temperature. In addition, a gap-like electronic excitation following the phonon region is analyzed in detail. We compare the results to the soft-edge behavior of the optical spectra characteristic for Mott-Hubbard insulators. Overall a consistent picture of the charge-transport mechanisms in LaTiO 3 emerges.

Apparent Giant Dielectric Constants, Dielectric Relaxation, and Ac‐Conductivity of Hexagonal Perovskites La1.2Sr2.7BO7.33 (B: Ru, Ir).

“…In the region between 3 THz and 30 THz (12.5 < log 10 ν < 13.5), resonance-like features show up, typical for phononic excitations. As was also found for other perovskite-related materials (e.g., [17,18,22]), there are three main contributions, with peaks in σ'(ν) at about 5 THz, 10 THz, and 16 THz (≈ 170 cm -1 , 330 cm -1 , and 530 cm -1 , respectively). In cubic perovskites, ABO 3 , the three infraredactive phonon excitations are ascribed to external, bending, and stretching modes.…”

“…its detection in the dc conductivity is consistent with our findings in the ac conductivity. VRH was also observed in various other transition metal oxides (see, e.g., [13,16,17,18,21] 6 not possible to reach a definite conclusion concerning the dimensionality of the charge transport.…”

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

“…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. The behavior of ͑ ͒ in LaTiO 3 is quite distinguished from that of Sr 2 IrO 4 , where ͑ ͒ of Sr 2 IrO 4 showed strong temperature dependence without a structural transition.…”

Magnetic structure of the Jahn-Teller systemLaTiO3

“…To exemplify this point, we consider the expectation value of H M , expressed in terms of the angles and , and, by the symmetries of the sublattice couplings, in terms of the couplings between the sublattice bonds ij = 12 and 13, 2 , and sin sin which are also of order 2 ͒, and the 2 correction of D 13 Dx ͑which is multiplied by sin sin ͒. Those contributions have been excluded from our calculation of the canting angles.…”

“…12 The presence of orbital order at low temperatures has also been concluded from measurements of the dielectric properties and the dynamical conductivity. 13 Furthermore, an orbital contribution to the specific heat, which is predicted by the orbitalliquid model, has not been found in experiment. 14 Hence from the recent experiments it must be concluded that the orbital-liquid model is inappropriate for LaTiO 3 .…”