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Direct observation of decoupled Dirac states at the interface between topological and normal insulators
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.ORCID iD: 0000-0002-7833-3943
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.ORCID iD: 0000-0002-8216-5321
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.ORCID iD: 0000-0001-8669-6886
2013 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 19, 195132Article in journal (Refereed) Published
Abstract [en]

Several proposed applications and exotic effects in topological insulators rely on the presence of helical Dirac states at the interface between a topological insulator and a normal insulator. In the present work, we have used low-energy angle-resolved photoelectron spectroscopy to uncover and characterize the interface states of Bi2Se3 thin films and Bi2Te3/Bi2Se3 heterostructures grown on Si(111). The results establish that Dirac fermions are indeed present at the topological-normal-insulator boundary and absent at the topological-topological-insulator interface. Moreover, it is demonstrated that band bending present within the topological-insulator films leads to a substantial separation of the interface and surface states in energy. These results pave the way for further studies and the realization of interface-related phenomena in topological-insulator thin-film heterostructures.

Place, publisher, year, edition, pages
American Physical Society , 2013. Vol. 88, no 19, 195132
Keyword [en]
Topological insulator, bismuth selenide, interface state, surface state
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-121940DOI: 10.1103/PhysRevB.88.195132ISI: 000327158600003Scopus ID: 2-s2.0-84888309073OAI: oai:DiVA.org:kth-121940DiVA: diva2:619746
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council
Note

QC 20131217

Available from: 2013-05-06 Created: 2013-05-06 Last updated: 2017-12-06Bibliographically 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.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2013:02
Keyword
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
Identifiers
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)
Opponent
Supervisors
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20130507

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

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Berntsen, Magnus H.Wojek, Bastian M.Tjernberg, Oscar

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