Filling of the Mott–Hubbard gap in the oxyhalides TiOCl and TiOBr induced by external pressure

Abstract

By pressure-dependent infrared microspectroscopy, we observe the filling of the Mott–Hubbard gap in TiOCl and TiOBr above a critical pressure P _c. Concomitant with the gap filling, a structural phase transition occurs at P _c. According to our pressure-dependent powder X-ray diffraction data, a mixture of the ambient-pressure orthorhombic Pmmn phase and a dimerized, monoclinic P2₁/m phase exists above P _c.

Keywords:

• Mott–Hubbard insulator
• optical response
• structural phase transition

Acknowledgements

We acknowledge the ANKA Angströmquelle Karlsruhe and the European Synchrotron Radiation Facility for the provision of beamtime. Financial support by the DFG (Emmy Noether-program, SFB 484, DFG-CL124/6-1) is acknowledged.