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# Topological crystalline insulator states in Pb1−xSnxSe

## Abstract

Topological insulators are a class of quantum materials in which time-reversal symmetry, relativistic effects and an inverted band structure result in the occurrence of electronic metallic states on the surfaces of insulating bulk crystals. These helical states exhibit a Dirac-like energy dispersion across the bulk bandgap, and they are topologically protected. Recent theoretical results have suggested the existence of topological crystalline insulators (TCIs), a class of topological insulators in which crystalline symmetry replaces the role of time-reversal symmetry in ensuring topological protection1,2. In this study we show that the narrow-gap semiconductor Pb1−xSnxSe is a TCI for x = 0.23. Temperature-dependent angle-resolved photoelectron spectroscopy demonstrates that the material undergoes a temperature-driven topological phase transition from a trivial insulator to a TCI. These experimental findings add a new class to the family of topological insulators, and we anticipate that they will lead to a considerable body of further research as well as detailed studies of topological phase transitions.

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## Acknowledgements

We would like to acknowledge V. Domukhovski and A. Reszka for structural and chemical composition analyses of the crystals, J. Adell for his help during our beam time at MAX-lab, S. Safai for her help in numerical calculations, and P. Kacman for critical reading of the manuscript. In Poland, this work was supported by the European Commission Network SemiSpinNet (PITN-GA-2008-215368) and by the European Regional Development Fund through the Innovative Economy grant (POIG.01.01.02-00-108/09). In Sweden, this work was made possible through support from the Knut and Alice Wallenberg Foundation and the Swedish Research Council.

## Author information

Authors

### Contributions

P.D., B.J.K. and T.B. planned and performed the ARPES studies at MAX-lab and analysed the data. K.D. and M.S. did magnetotransport measurements. K.D. performed conductivity tensor analysis and wrote part of the manuscript. R.B. carried out theoretical band structure calculations. A.S. grew the crystals. E.Ł. characterized the crystals with the atomic force microscopy method. B.M.W., M.H.B., T.B. and O.T. performed the BALTAZAR ARPES measurements. B.M.W., M.H.B. and O.T. performed ARPES data analysis and wrote part of the manuscript. T.S. initiated the project and wrote part of the manuscript. All authors contributed to data analysis and editing of the manuscript.

### Corresponding authors

Correspondence to O. Tjernberg or T. Story.

## Ethics declarations

### Competing interests

The authors declare no competing financial interests.

## Supplementary information

### Supplementary Information

Supplementary Information (PDF 968 kb)

## Rights and permissions

Reprints and Permissions

Dziawa, P., Kowalski, B., Dybko, K. et al. Topological crystalline insulator states in Pb1−xSnxSe. Nature Mater 11, 1023–1027 (2012). https://doi.org/10.1038/nmat3449

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