Angle Resolved Photoemission Spectroscopy Study on Layered Oxy-pnictide BaTi2As2O

Recently, superconductivity has been discovered in Ba$_{1-x}$Na$_x$Ti$_2$Sb$_2$O, a titanium-based oxy-pnictide with an anti-CuO$_2$ type Ti$_2$O plane and a CDW/SDW anomaly at 54K. The isostructured BaTi$_2$As$_2$O, where signs of CDW/SDW at 200K has been observed, could be viewed as one of the parent compounds of this new family of superconductors. Here we report the Angle Resolved Photoemission Spectroscopy Study on BaTi$_2$As$_2$O. Parallel sections were found in Fermi surface structure, indicating possible nesting condition. The orbital character of bands supports the important role of Ti-Ti direct interaction. No abrupt change was observed at the critical temperature; however, spectral weight change takes place at wide energy scale both above and below the critical temperature, revealing the strong electron-lattice coupling effect in this system.