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Chiral charge order in 1T-TiSe2: Importance of lattice degrees of freedom


Monney,  Claude
Physical Chemistry, Fritz Haber Institute, Max Planck Society;

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Zenker, B., Fehske, H., Beck, H., Monney, C., & Bishop, A. R. (2013). Chiral charge order in 1T-TiSe2: Importance of lattice degrees of freedom. Physical Review B, 88(7): 075138. doi:10.1103/PhysRevB.88.075138.

We address the question of the origin of the recently discovered chiral property of the charge-density-wave phase in 1T-TiSe2, which so far lacks a microscopic understanding. We argue that the lattice degrees of freedom seem to be crucial for this novel phenomenon. We motivate a theoretical model that takes into account one valence and three conduction bands, a strongly screened Coulomb interaction between the electrons, as well as the coupling of the electrons to a transverse optical phonon mode. The Falicov-Kimball model extended in this way possesses a charge-density-wave state at low temperatures, which is accompanied by a periodic lattice distortion. The charge ordering is driven by a lattice deformation and electron-hole pairing (excitonic) instability in combination. We show that both electron-phonon interaction and phonon-phonon interaction must be taken into account at least up to quartic order in the lattice displacement to achieve a stable chiral charge order. The chiral property is exhibited in the ionic displacements. Furthermore, we provide the ground-state phase diagram of the model and give an estimate of the electron-electron and electron-phonon interaction constants for 1T-TiSe2.