| 1. |
- Dziawa, P., et al.
(författare)
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Defect Free PbTe Nanowires Grown by Molecular Beam Epitaxy on GaAs(111)B Substrates
- 2010
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 10:1, s. 109-113
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Tidskriftsartikel (refereegranskat)abstract
- The molecular beam epitaxial growth of PbTe nanowires oil GaAs(111)B substrates is reported. The growth process was based oil the Au-catalyzed vapor-liquid-solid mechanism. These nanowires grow along the [100] axis; they are perpendicular to the substrate, have tapered shapes, and have diameters of about 90 rim at the base and 60 run at the top. High resolution transmission electron microscopy pictures reveal that the PbTe nanowires have a rock-salt structure and, in contrast to the one-dimensional structures of III-V and II-VI compound semiconductors such as GaAs. InAs, or ZnTe, are free from stacking faults. A theoretical analysis of these experimental findings, which is based oil ab initio modeling of the PbTe nanowires, is also presented.
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| 2. |
- Polley, Craig, et al.
(författare)
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Observation of topological crystalline insulator surface states on (111)-oriented Pb1-xSnxSe films
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:7, s. 075317-
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Tidskriftsartikel (refereegranskat)abstract
- We present angle-resolved photoemission spectroscopy measurements of the surface states on in-situ grown (111) oriented films of Pb1-xSnxSe, a three-dimensional topological crystalline insulator. We observe surface states with Dirac-like dispersion at (Gamma) over bar and (M) over bar in the surface Brillouin zone, supporting recent theoretical predictions for this family of materials. We study the parallel dispersion isotropy and Dirac-point binding energy of the surface states, and perform tight-binding calculations to support our findings. The relative simplicity of the growth technique is encouraging, and suggests a clear path for future investigations into the role of strain, vicinality, and alternative surface orientations in (Pb,Sn)Se solid solutions.
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| 3. |
- Wojek, Bastian M., et al.
(författare)
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Spin-polarized (001) surface states of the topological crystalline insulator Pb0.73Sn0.27Se
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 87:11, s. 115106-
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Tidskriftsartikel (refereegranskat)abstract
- We study the nature of (001) surface states in Pb0.73Sn0.27Se in the newly discovered topological-crystalline-insulator (TCI) phase as well as the corresponding topologically trivial state above the band-gap-inversion temperature. Our calculations predict not only metallic surface states with a nontrivial chiral spin structure for the TCI case, but also nonmetallic (gapped) surface states with nonzero spin polarization when the system is a normal insulator. For both phases, angle- and spin-resolved photoelectron spectroscopy measurements provide conclusive evidence for the formation of these (001) surface states in Pb0.73Sn0.27Se, as well as for their chiral spin structure.
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| 4. |
- Dziawa, P., et al.
(författare)
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Topological crystalline insulator states in Pb1-xSnxSe
- 2012
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Ingår i: Nature Materials. - 1476-1122 .- 1476-4660. ; 11:12, s. 1023-1027
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Tidskriftsartikel (refereegranskat)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 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.
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| 5. |
- Wojek, Bastian M., et al.
(författare)
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Band inversion and the topological phase transition in (Pb,Sn)Se
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:16, s. 161202-
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Tidskriftsartikel (refereegranskat)abstract
- The recent discovery of a topological phase transition in IV-VI narrow-gap semiconductors has revitalized the decades-old interest in the bulk band inversion occurring in these materials. Here we systematically study the (001) surface states of Pb1-xSnxSe mixed crystals by means of angle-resolved photoelectron spectroscopy in the parameter space 0 <= x <= 0.37 and 300 K >= T >= 9 K. Using the surface-state observations, we monitor directly the topological phase transition in this solid solution and gain valuable information on the evolution of the underlying fundamental band gap of the system. In contrast to common model expectations, the band-gap evolution appears to be nonlinear as a function of the studied parameters, resulting in the measuring of a discontinuous band-inversion process. This finding signifies that the anticipated gapless bulk state is in fact not a stable configuration and that the topological phase transition therefore exhibits features akin to a first-order transition.
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| 6. |
- Wojek, Bastian M., et al.
(författare)
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Direct observation and temperature control of the surface Dirac gap in a topological crystalline insulator
- 2015
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Since the advent of topological insulators hosting Dirac surface states, efforts have been made to gap these states in a controllable way. A new route to accomplish this was opened up by the discovery of topological crystalline insulators where the topological states are protected by crystal symmetries and thus prone to gap formation by structural changes of the lattice. Here we show a temperature-driven gap opening in Dirac surface states within the topological crystalline insulator phase in (Pb,Sn) Se. By using angle-resolved photoelectron spectroscopy, the gap formation and mass acquisition is studied as a function of composition and temperature. The resulting observations lead to the addition of a temperature-and composition-dependent boundary between massless and massive Dirac states in the topological phase diagram for (Pb,Sn) Se (001). Overall, our results experimentally establish the possibility to tune between massless and massive topological states on the surface of a topological system.
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