Layered compounds AFBiS2: superior birefringent crystals

TL;DR

This paper investigates layered compounds AFBiS2, revealing they exhibit exceptionally high birefringence, with MgFBiS2 reaching a birefringence of 1.65, surpassing previously known materials and providing insights into their origin.

Contribution

It introduces new AFBiS2 compounds with superior birefringence and analyzes the origin of giant birefringence in these layered crystals.

Findings

MgFBiS2 has the highest birefringence of 1.65.

SrFBiS2 exhibits birefringence up to 1.28.

The origin of giant birefringence is discussed in detail.

Abstract

Stimulated by the discovery of the giant birefringence (GBF) in LaOBiS2 (H. Wang, arxiv: 1304.5032), we check SrFBiS2 and find a superior birefringence up to 1.28. Naturally, AF layer (i.e., SrF) is considered to be of important and is demonstrated by the further study on AFBiS2 (A=Mg, Ca, Ba). Interestingly, MgFBiS2 shows the largest birefringence of 1.65. Furthermore, the origin of GBF is discussed in detail.