# A novel quasi-one-dimensional topological insulator in bismuth iodide β-Bi4I4

## Abstract

Recent progress in the field of topological states of matter1,2 has largely been initiated by the discovery of bismuth and antimony chalcogenide bulk topological insulators (TIs; refs 3,4,5,6), followed by closely related ternary compounds7,8,9,10,11,12,13,14,15,16 and predictions of several weak TIs (refs 17,18,19). However, both the conceptual richness of Z2 classification of TIs as well as their structural and compositional diversity are far from being fully exploited. Here, a new Z2 topological insulator is theoretically predicted and experimentally confirmed in the β-phase of quasi-one-dimensional bismuth iodide Bi4I4. The electronic structure of β-Bi4I4, characterized by Z2 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  point of the surface Brillouin zone and showing no dispersion with the photon energy, thus being fully consistent with the theoretical prediction.

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## References

1. 1

Hasan, M. Z. & Kane, C. L. Colloquium: Topological insulators. Rev. Mod. Phys. 82, 3045–3067 (2010).

2. 2

Qi, X.-L. & Zhang, S.-C. Topological insulators and superconductors. Rev. Mod. Phys. 83, 1057–1110 (2011).

3. 3

Xia, Y. et al. Observation of a large-gap topological-insulator class with a single Dirac cone on the surface. Nature Phys. 5, 398–402 (2009).

4. 4

Zhang, H. et al. Topological insulators in Bi2Se3, Bi2Te3 and Sb2Te3 with a single Dirac cone on the surface. Nature Phys. 5, 438–442 (2009).

5. 5

Chen, Y. L. et al. Experimental realization of a three-dimensional topological insulator, Bi2Te3 . Science 325, 178–181 (2009).

6. 6

Hsieh, D. et al. A tunable topological insulator in the spin helical Dirac transport regime. Nature 460, 1101–1105 (2009).

7. 7

Yan, B. & Zhang, S.-C. Topological materials. Rep. Prog. Phys. 75, 096501 (2012).

8. 8

Ando, Y. Topological insulator materials. J. Phys. Soc. Jpn 82, 102001 (2013).

9. 9

Neupane, M. et al. Topological surface states and Dirac point tuning in ternary topological insulators. Phys. Rev. B 85, 235406 (2012).

10. 10

Okamoto, K. et al. Observation of a highly spin-polarized topological surface state in GeBi2Te4 . Phys. Rev. B 86, 195304 (2012).

11. 11

Eremeev, S. V. et al. Atom-specific spin mapping and buried topological states in a homologous series of topological insulators. Nature Commun. 3, 635 (2012).

12. 12

Souma, S. et al. Topological surface states in lead-based ternary telluride Pb(Bi1−xSbx)2Te4 . Phys. Rev. Lett. 108, 116801 (2012).

13. 13

Kuroda, K. et al. Experimental verification of PbBi2Te4 as a 3D topological insulator. Phys. Rev. Lett. 108, 206803 (2012).

14. 14

Sato, T. et al. Direct evidence for the Dirac-cone topological surface states in the ternary chalcogenide TlBiSe2 . Phys. Rev. Lett. 105, 136802 (2010).

15. 15

Kuroda, K. et al. Experimental realization of a three-dimensional topological insulator phase in ternary chalcogenide TlBiSe2 . Phys. Rev. Lett. 105, 146801 (2010).

16. 16

Chen, Y. L. et al. Single Dirac cone topological surface state and unusual thermoelectric property of compounds from a new topological insulator family. Phys. Rev. Lett. 105, 266401 (2010).

17. 17

Yan, B., Müchler, L. & Felser, C. Prediction of weak topological insulators in layered semiconductors. Phys. Rev. Lett. 109, 116406 (2012).

18. 18

Rasche, B. et al. Stacked topological insulator built from bismuth-based graphene sheet analogues. Nature Mater. 12, 422–425 (2013).

19. 19

Tang, P. et al. Weak topological insulators induced by the interlayer coupling: A first-principles study of stacked Bi2TeI. Phys. Rev. B 89, 041409 (2014).

20. 20

von Schnering, H. G., von Benda, H. & Kalveram, C. Wismutmonojodid BiJ, eine Verbindung mit Bi(0) und Bi(II). Z. Anorg. Allg. Chem. 438, 37–52 (1978).

21. 21

Isaeva, A., Rasche, B. & Ruck, M. Bismuth-based candidates for topological insulators: Chemistry beyond Bi2Te3 . Phys. Status Solidi RRL 7, 39–49 (2013).

22. 22

Filatova, T. G. et al. Electronic structure, galvanomagnetic and magnetic properties of the bismuth subhalides Bi4I4 and Bi4Br4 . J. Solid State Chem. 180, 1103–1109 (2007).

23. 23

Fu, L. & Kane, C. L. Topological insulators with inversion symmetry. Phys. Rev. B 76, 045302 (2007).

24. 24

Zhou, J.-J., Feng, W., Liu, C.-C., Guan, S. & Yao, Y. Large-gap quantum spin Hall insulator in single layer bismuth monobromide Bi4Br4 . Nano Lett. 14, 4767–4771 (2014).

25. 25

Vidal, J., Zhang, X., Yu, L., Luo, J. W. & Zunger, A. False-positive and false-negative assignments of topological insulators in density functional theory and hybrids. Phys. Rev. B 84, 041109 (2011).

26. 26

Hedin, L. & Lundqvist, S. in Solid State Physics Vol. 23 (eds Frederick, S. D. T. & Henry, E.) 1–181 (Academic, 1970).

27. 27

Hybertsen, M. S. & Louie, S. G. Electron correlation in semiconductors and insulators: Band gaps and quasiparticle energies. Phys. Rev. B 34, 5390–5413 (1986).

28. 28

Yazyev, O. V., Kioupakis, E., Moore, J. E. & Louie, S. G. Quasiparticle effects in the bulk and surface-state bands of Bi2Se3 and Bi2Te3 topological insulators. Phys. Rev. B 85, 161101 (2012).

29. 29

Nechaev, I. A. et al. Evidence for a direct band gap in the topological insulator Bi2Se3 from theory and experiment. Phys. Rev. B 87, 121111 (2013).

30. 30

Aguilera, I., Friedrich, C., Bihlmayer, G. & Blügel, S. GW study of topological insulators Bi2Se3, Bi2Te3, and Sb2Te3: Beyond the perturbative one-shot approach. Phys. Rev. B 88, 045206 (2013).

31. 31

Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).

32. 32

Giannozzi, P. et al. QUANTUM ESPRESSO: A modular and open-source software project for quantum simulations of materials. J. Phys. Condens. Matter 21, 395502 (2009).

33. 33

Dal Corso, A. & Mosca Conte, A. Spin–orbit coupling with ultrasoft pseudopotentials: Application to Au and Pt. Phys. Rev. B 71, 115106 (2005).

34. 34

Deslippe, J. et al. BerkeleyGW: A massively parallel computer package for the calculation of the quasiparticle and optical properties of materials and nanostructures. Comput. Phys. Commun. 183, 1269–1289 (2012).

35. 35

Mostofi, A. A. et al. Wannier90: A tool for obtaining maximally-localised Wannier functions. Comput. Phys. Commun. 178, 685–699 (2008).

36. 36

Umerski, A. Closed-form solutions to surface Green’s functions. Phys. Rev. B 55, 5266–5275 (1997).

## Acknowledgements

We thank J. H. Dil, M. Ruck, M. Richter and K. Koepernik for fruitful discussions, H. Lee for discussions regarding the computational methodology, B. Kim for support during the beamtime on Merlin, M. Münch, K. Zechel and A. Weiz for assistance with synthesis and SEM/EDX measurements. We are grateful to E. Schmid for ultramicrotomy, to U. Kaiser and C. T. Koch for providing beam time for the TEM characterization. G.A. and O.V.Y. acknowledge support by the Swiss NSF (grant No. PP00P2_133552), ERC project ‘TopoMat’ (grant No. 306504) and NCCR-MARVEL. A.I. acknowledges the Priority Program 1666 ‘Topological Insulators’ of the Deutsche Forschungsgemeinschaft (DFG, grant No. IS 250/1-1). L.M. acknowledges support by the Swiss NSF (grant No. PA00P21-36420). The Advanced Light Source and the laser-based ARPES measurements, part of the Ultrafast Materials Program at Lawrence Berkeley National Laboratory, are supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-AC02-05CH11231. W.V.d.B. acknowledges the Carl-Zeiss Foundation. Electronic structure calculations have been performed at the Swiss National Supercomputing Centre (CSCS) under project s515.

## Author information

O.V.Y. initiated and directed this research project; G.A. performed first-principles calculations; A.I. pointed out, synthesized and characterized the material; L.M. conducted the ARPES measurements, together with R.M. and W.Z. for the laser-based experiments; L.M., J.C.J. and M.G. analysed the ARPES data; A.P. and L.F. carried out the transport measurements; T.G.F. and A.N.K. performed and optimized sample preparation; W.V.d.B. assisted in the TEM experiments; Y.K., K.S.K., J.D.D., A.L., E.R. and A.B. assisted in the ARPES measurements and data analysis. All authors contributed to discussions and manuscript revision.

Correspondence to Oleg V. Yazyev.

## Ethics declarations

### Competing interests

The authors declare no competing financial interests.

## Supplementary information

### Supplementary Information

Supplementary Information (PDF 5947 kb)

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Autès, G., Isaeva, A., Moreschini, L. et al. A novel quasi-one-dimensional topological insulator in bismuth iodide β-Bi4I4. Nature Mater 15, 154–158 (2016). https://doi.org/10.1038/nmat4488

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