β-Bi4I4

I had blogged it earlier when it was still just an APS meeting abstract, now here it is.

http://www.nature.com/nmat/journal/v15/n2/full/nmat4543.html

A novel quasi-one-dimensional topological insulator in bismuth iodide β-Bi_{4}I_{4}, A novel quasi-one-dimensional topological insulator in bismuth iodide β-Bi4I4, Gabriel Autès, Anna Isaeva, Luca Moreschini, Jens C. Johannsen, Andrea Pisoni, Ryo Mori, Wentao Zhang, Taisia G. Filatova, Alexey N. Kuznetsov, László Forró, Wouter Van den Broek, Yeongkwan Kim, Keun Su Kim, Alessandra Lanzara, Jonathan D. Denlinger, Eli Rotenberg, Aaron Bostwick, Marco Grioni and Oleg V. Yazyev, Nature Materials, 15, 154–158 (14 December 2015), doi:10.1038/nmat4488

Recent progress in the field of topological states of matter has largely been initiated by the discovery of bismuth and antimony chalcogenide bulk topological insulators, followed by closely related ternary compounds and predictions of several weak TIs. However, both the conceptual richness of *Z*_{2} classification of TIs as well as their structural and compositional diversity are far from being fully exploited. Here, a new *Z*_{2} topological insulator is theoretically predicted and experimentally confirmed in the β-phase of quasi-one-dimensional bismuth iodide β-Bi_{4}I_{4}. The electronic structure of β-Bi_{4}I_{4}, characterized by *Z*_{2} invariants (1;110), is in proximity of both the weak TI phase (0;001) and the trivial insulator phase (0;000). Our angle-resolved photoemission spectroscopy measurements performed on the (001) surface reveal a highly anisotropic band-crossing feature located at the **M**^{–} point of the surface Brillouin zone and showing no dispersion with the photon energy, thus being fully consistent with the theoretical prediction.

**See also**: http://www.nature.com/nmat/journal/v15/n2/full/nmat4543.html

Topological insulators: Quasi-1D topological insulators, Huaqing Huang and Wenhui Duan, Nature Materials, 15, 129–130 (22 January 2016), doi:10.1038/nmat4543

Bismuth iodide Bi_{4}I_{4}, composed of quasi-one-dimensional molecular chains, was theoretically predicted and now has been experimentally verified to be a novel strong topological insulator.

https://nanotheoryou.wikispaces.com/file/view/News+and+views-+Quasi-1D+topological+insulators.pdf

So it’s nice to see this subject taken to completion.