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An experimental setup for high resolution 10.5 eV laser-based angle-resolved photoelectron spectroscopy using a time-of-flight electron analyzer
KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.ORCID iD: 0000-0002-7833-3943
KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.ORCID iD: 0000-0001-8669-6886
2011 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 82, no 9, 095113- p.Article in journal (Refereed) Published
Abstract [en]

We present an experimental setup for laser-based angle-resolved time-of-flight photoemission. Using a picosecond pulsed laser, photons of energy 10.5 eV are generated through higher harmonic generation in xenon. The high repetition rate of the light source, variable between 0.2 and 8 MHz, enables high photoelectron count rates and short acquisition times. By using a time-of-flight analyzer with angle-resolving capabilities, electrons emitted from the sample within a circular cone of up to +/- 15 degrees can be collected. Hence, simultaneous acquisition of photoemission data for a complete area of the Brillouin zone is possible. The current photon energy enables bulk sensitive measurements, high angular resolution, and the resulting covered momentum space is large enough to enclose the entire Brillouin zone in cuprate high-T(c) superconductors. Fermi edge measurements on polycrystalline Au shows an energy resolution better than 5 meV. Data from a test measurement of the Au(111) surface state are presented along with measurements of the Fermi surface of the high-T(c) superconductor Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi2212).

Place, publisher, year, edition, pages
2011. Vol. 82, no 9, 095113- p.
Keyword [en]
Brillouin zones, Fermi surface, high-temperature superconductors, lasers, photoelectron spectroscopy, photoemission, time of flight spectroscopy
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-46858DOI: 10.1063/1.3637464ISI: 000295621100060ScopusID: 2-s2.0-80053541533OAI: diva2:454346
Knut and Alice Wallenberg FoundationSwedish Research Council

QC 20111107

Available from: 2011-11-07 Created: 2011-11-07 Last updated: 2013-05-07Bibliographically 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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