Regensburg 2004 – scientific programme

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TT: Tiefe Temperaturen

TT 24: Postersitzung III: Korrelierte Elektronen, ”Orbital Physics”

TT 24.46: Poster

Wednesday, March 10, 2004, 14:30–19:00, Poster A

Orbital occupation and momentum in LaTiO₃ — •M.W. Haverkort¹, Z. Hu¹, H. Roth¹, T. Lorenz¹, C. de Nadai², N.B. Brookes², A. Tanaka³, H.H. Hsieh⁴, H.-J. Lin⁴, C.T. Chen⁴, and L.H. Tjeng¹ — ¹II. Physikalisches Institut, Universität zu Köln — ²ESRF, Grenoble, France — ³ADSM, Hiroshima, Japan — ⁴NSRRC, Hsinchu, Taiwan

LaTiO3 is an antiferromagnetic insulator with a magnetic ordering temperature of T_N≈ 145 K. Neutron measurements reveal a magnetic moment of 0.45∼0.57 µ_B, significantly less than the 1 µ_B expected for a S = 1/2 system (Ti = 3d¹). One may envision that this discrepancy can be ascribed to the presence of an anti-parallel aligned orbital momentum in this quasi cubic material. However, neutron data also found an almost perfect isotropic spin wave spectrum with an extremely low spin gap, indicative for the absence of an orbital moment. An orbital liquid model is then proposed to explain these data. We have carried out detailed temperature dependent soft-x-ray absorption and circularly-polarized/spin-resolved photoemission experiments. We find that the orbital moment is practically quenched, in agreement with the neutron spin wave data. Using the results from LDA and LDA+U calculations, we infer that this quenching is caused by non-cubic crystal fields associated with the small but non-negligible non-cubic distortions in LaTiO₃. These crystal fields are much stronger than the spin-orbit interaction, and crucial for the explanation of the lineshape and the lack of temperature dependence of the spectra. It seems that these conditions do not favor the formation of an orbital liquid.