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[Fizinfo] Szeminarium - C.A. Kuntscher (Ausburg)

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  • From: Mihaly Gyorgy <mihaly AT>
  • To: fizinfo AT
  • Subject: [Fizinfo] Szeminarium - C.A. Kuntscher (Ausburg)
  • Date: Tue, 27 Jan 2009 12:08:01 +0100
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a BME Fizikai Intézet, Fizika Tanszék szemináriumára

Prof. C. A. Kuntscher

Filling of the Mott-Hubbard gap and structural phase transitions
in the oxyhalides TiOCl and TiOBr induced by external pressure

University of Augsburg

Az elõadás helye: BME Fizikai Intézet szemináriumi szoba
Budafoki út 8. F-épület, III. lépcsõház, magasföldszint

Ideje: 2009. február 5. csütörtök, 10:00.

The titanium oxyhalides TiOCl and TiOBr are low-dimensional materials which undergo unconventional transitions to a spin-Peierls state via a structural incommensurate state.
With the electronic configuration 3d^1 these compounds are Mott-Hubbard insulators with a charge gap of approximately 2 eV. They have been discussed to exhibit a resonating valence bond state and high-temperature superconductivity upon doping. However, despite several attempts, up to now a metallization of TiOX (X= Cl, Br) upon doping was not successful.

Our recent pressure-dependent infrared spectroscopic investigations on TiOX [1] suggest that the application of external pressure is an alternative way to induce an insulator-to-metal transition in TiOX. By infrared microspectroscopy we could show the filling of the Mott-Hubbard gap at the critical pressure 16 GPa (14 GPa) for TiOCl (TiOBr) at room temperature. According to our pressure-dependent x-ray powder-diffraction data, the gap closure coincides with a structural phase transition. These findings are discussed in the context of recent electric transport experiments on TiOCl under pressure [2] and theoretical predictions of pressure-induced phase transitions in TiOCl by an ab initio molecular dynamics study [3].

[1] C. A. Kuntscher et al., Phys. Rev. B 74, 184402 (2006); C. A. Kuntscher et al., Phys. Rev. B 76, 24110 (R) (2007); C. A. Kuntscher et al., Phys. Rev. 78, 035106 (2008).
[2] Forthaus et al., Phys. Rev. B 77, 165121 (2008).
[3] Y-Z. Zhang et al., Phys. Rev. Lett. 101, 136406 (2008).

G. Mihaly
Department of Physics
Budapest University of Technology and Economics

  • [Fizinfo] Szeminarium - C.A. Kuntscher (Ausburg), Mihaly Gyorgy, 01/27/2009

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