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Topological crystalline insulator states in Pb1-xSnxSe
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2012 (English)In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 11, no 12, 1023-1027 p.Article in journal (Refereed) Published
Abstract [en]

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 protection(1,2). 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.

Place, publisher, year, edition, pages
2012. Vol. 11, no 12, 1023-1027 p.
Keyword [en]
Inversion, Bands, Performance, Alloys, Phase, Snte
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-109176DOI: 10.1038/NMAT3449ISI: 000311432600019ScopusID: 2-s2.0-84870037398OAI: diva2:582790
Knut and Alice Wallenberg FoundationSwedish Research Council

QC 20150623

Available from: 2013-01-07 Created: 2012-12-21 Last updated: 2015-06-23Bibliographically approved
In thesis
1. Consequences of a non-trivial band-structure topology in solids: Investigations of topological surface and interface states
Open this publication in new window or tab >>Consequences of a non-trivial band-structure topology in solids: Investigations of topological surface and interface states
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The development and characterization of experimental setups for angle-resolved photoelectron spectroscopy (ARPES) and spin- and angle-resolved photoelectron spectroscopy (SARPES) is described. Subsequently, the two techniques are applied to studies of the electronic band structure in topologically non-trivial materials.

The laser-based ARPES setup works at a photon energy of 10.5 eV and a typical repetition rate in the range 200 kHz to 800 kHz. By using a time-of-flight electron energy analyzer electrons emitted from the sample within a solid angle of up to ±15 degrees can be collected and analyzed simultaneously. The SARPES setup is equipped with a traditional hemispherical electron energy analyzer in combination with a mini-Mott electron polarimeter. The system enables software-controlled switching between angle-resolved spin-integrated and spin-resolved measurements, thus providing the possibility to orient the sample by mapping out the electronic band structure using ARPES before performing spin-resolved measurements at selected points in the Brillouin zone.

Thin films of the topological insulators (TIs) Bi2Se3, Bi2Te3 and Sb2Te3 are grown using e-beam evaporation and their surface states are observed by means of ARPES. By using a combination of low photon energies and cryogenic sample temperatures the topological states originating from both the vacuum interface (surface) and the substrate interface are observed in Bi2Se3 films and Bi2Se3/Bi2Te3 heterostructures, with total thicknesses in the ultra-thin limit (six to eight quintuple layers), grown on Bi-terminated Si(111) substrates. Band alignment between Si and Bi2Se3 at the interface creates a band bending through the films. The band bending is found to be independent of the Fermi level (EF) position in the bulk of the substrate, suggesting that the surface pinning of EF in the Si(111) substrate remains unaltered after deposition of the TI films. Therefore, the type and level of doping of the substrate does not show any large influence on the size of the band bending.

Further, we provide experimental evidence for the realization of a topological crystalline insulator (TCI) phase in the narrow-band semiconductor Pb1−xSnxSe. The TCI phase exists for temperatures below the transition temperature Tc and is characterized by an inverted bulk band gap accompanied by the existence of non-gapped surface states crossing the band gap. Above Tc the material is in a topologically trivial phase where the surface states are gapped. Thus, when lowering the sample temperature across Tc a topological phase transition from a trivial insulator to a TCI is observed. SARPES studies indicate a helical spin structure of the surface states both in the topologically trivial and the TCI phase.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. x, 82 p.
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2013:02
spin- and angle-resolved photoelectron spectroscopy, time-of-flight analyzer, laser based light source, topological insulator, topological crystalline insulator, thin films, surface state, interface state, Bi2Se3, Pb1-xSnxSe
National Category
Physical Sciences Condensed Matter Physics
urn:nbn:se:kth:diva-121974 (URN)978-91-7501-735-8 (ISBN)
Public defence
2013-05-31, Sal D, KTH-Forum, Isafjordsgatan 39, Kista, 10:00 (English)
Swedish Research CouncilKnut and Alice Wallenberg Foundation

QC 20130507

Available from: 2013-05-07 Created: 2013-05-06 Last updated: 2013-05-07Bibliographically approved

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