Giant Birefringence in Layered Compound LaOBiS2.

Birefringent crystals (BFCs) have been extensively used in imaging spectrometers, laser devices, and optical components. Seeking new BFCs is important for both fundamental research and industrial applications. Employing first-principles density functional theory, we find that LaOBiS2 (space group: P4/nmm) appearing in the parent phase of the recently discovered BiS2-superconductor exhibits superior birefringence with a maximum value of 2.94, which is 13.4 times larger than the extensively used YVO4 (0.22). Furthermore, LaOBiS2 is an indirect semiconductor with a band gap of 0.9 eV, which is suitable for optical applications. The origin of giant inherent birefringence is also discussed. [ABSTRACT FROM AUTHOR]