Black Phosphorus and Black Arsenic–Phosphorus

See:

Black Arsenic–Phosphorus: Layered Anisotropic Infrared Semiconductors with Highly Tunable Compositions and Properties,

Bilu Liu, Marianne Köpf, Ahmad N. Abbas, Xiaomu Wang, Qiushi Guo, Yichen Jia, Fengnian Xia, Richard Weihrich, Frederik Bachhuber, Florian Pielnhofer, Han Wang, Rohan Dhall, Stephen B. Cronin, Mingyuan Ge, Xin Fang, Tom Nilges, and Chongwu Zhou*,

Adv. Mater. 2015, 27, 4423–4429.

Also:

Black phosphorus field-effect transistors,

Likai Li, Yijun Yu, Guo Jun Ye, Qingqin Ge, Xuedong Ou, Hua Wu, Donglai Feng, Xian Hui Chen & Yuanbo Zhang,

Nature Nanotechnology 9, 372–377 (2014)

Bilayer Bismuth and few layer Antimony are semi metals without a gap, and likely possess topological edge states. SnTe and PbTe are also semimetals and can exist in the 2D limit, and are topological crystalline insulators. Monolayer Sn is also being investigated at as a topological semimetal. 

Great, I will look into these materials. Thank you for your insight!

This is great! Thank you so much!