Hamburg 2001 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 11: Fachsymposium: Eindimensionale Übergangsmetalle

TT 11.1: Hauptvortrag

Dienstag, 27. März 2001, 14:30–15:00, A

Gigantic optical nonlinearity in one-dimensional Mott-Hubbard insulators — •Hideo Kishida¹, Hiroshi Okamoto^1,2, and Yoshinori Tokura^2,3,4 — ¹Department of Advanced Materials Science, Univ. of Tokyo, Hongo, Tokyo 113-0033 JAPAN — ²CERC — ³Department of Applied Physics, Univ. of Tokyo — ⁴JRCAT

Third-order nonlinear optical response has been studied in one-dimensional (1D) Mott insulators, Sr₂CuO₃, Ca₂CuO₃, and halogen-bridged Ni compounds [Ni(chxn)₂X]Y₂ (X=Br,Cl;Y=Br,Cl,(NO₃)₂), by electroreflectance (ER) and third harmonic generation (THG) spectroscopy. From the ER measurements, Im χ⁽³⁾(−ω;0,0,ω) is evaluated to be χ⁽³⁾ ≈ 10⁻⁸ to 10⁻⁵ esu [1], which is significantly larger than that in conjugated polymers and platinum compounds, 10⁻¹⁰ to 10⁻⁸esu. An analysis of the spectral shape of Im χ⁽³⁾(−ω;0,0,ω) (ER) and |χ⁽³⁾(−3ω; ω, ω, ω)| (THG) reveals that the strong enhancement of nonlinear optical response originates from the large transition dipole moments between nearly degenerate odd and even charge transfer states. We compare the experimental χ⁽³⁾ spectra with theoretical ones[2], which are based on the concept of spin-charge separation inherent to 1D correlated electron systems.

[1]H. Kishida et al., Nature 405, 929 (2000). [2]Y. Mizuno et al., Phys. Rev. B62, 4769 (2000).