Giant birefringence in layered compound LaOBiS2

TL;DR

This study predicts that LaOBiS2, a layered compound related to BiS2 superconductors, exhibits exceptionally high birefringence and suitable optical properties, making it promising for optical device applications.

Contribution

First-principles DFT calculations reveal LaOBiS2's giant birefringence and potential as an optical material, expanding the search for advanced birefringent crystals.

Findings

LaOBiS2 has a birefringence of 2.94, 13.4 times larger than YVO4.

LaOBiS2 is an indirect semiconductor with a 0.9 eV band gap.

The origin of giant birefringence is discussed.

Abstract

Birefringent crystals (BFC) have been extensively used in imaging spectrometer, laser devices, and optical components. Seeking new BFC is of important for both fundamental research and industrial application. Employed first-principles density functional theory (DFT), we found that LaOBiS2 (space group P4/nmm), the parent phase of 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 discussed.