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Infrared optical properties of the spin-1/2 quantum magnet $TiOCl$

G. Caimi·L. Degiorgi·N. N. Kovaleva·P. Lemmens·F. C. Chou
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Abstract

We report results on the electrodynamic response of $TiOCl$, a low-dimensional spin-1/2 quantum magnet that shows a spin gap formation for T$<T_{c1}$= 67 $K$. The Fano-like shape of a few selected infrared active phonons suggests an interaction between lattice vibrations and a continuum of low frequency (spin) excitations. The temperature dependence of the phonon mode parameters extends over a broad temperature range well above $T_{c1}$, indicating the presence of an extended fluctuation regime. In the temperature interval between 200 $K$ and $T_{c1}$ there is a progressive dimensionality crossover (from two to one), as well as a spectral weight shift from low towards high frequencies. This allows us to identify a characteristic energy scale of about 430 $K$, ascribed to a pseudo spin-gap.

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G. Caimi, L. Degiorgi, N. N. Kovaleva, P. Lemmens, F. C. Chou. 2003-08-14. Infrared optical properties of the spin-1/2 quantum magnet $TiOCl$. https://doi.org/10.1103/physrevb.69.125108

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