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Realization of a vertical topological p-n junction in epitaxial Sb2Te3/Bi2Te3 heterostructures.

Eschbach M, Młyńczak E, Kellner J, Kampmeier J, Lanius M, Neumann E, Weyrich C, Gehlmann M, Gospodarič P, Döring S, Mussler G, Demarina N, Luysberg M, Bihlmayer G, Schäpers T, Plucinski L, Blügel S, Morgenstern M, Schneider CM, Grützmacher D - Nat Commun (2015)

Bottom Line: Three-dimensional (3D) topological insulators are a new state of quantum matter, which exhibits both a bulk band structure with an insulating energy gap as well as metallic spin-polarized Dirac fermion states when interfaced with a topologically trivial material.Here we show a direct experimental proof by angle-resolved photoemission of the realization of a vertical topological p-n junction made of a heterostructure of two different binary 3D TI materials Bi2Te3 and Sb2Te3 epitaxially grown on Si(111).We demonstrate that the chemical potential is tunable by about 200 meV when decreasing the upper Sb2Te3 layer thickness from 25 to 6 quintuple layers without applying any external bias.

View Article: PubMed Central - PubMed

Affiliation: Forschungszentrum Jülich GmbH, Peter Grünberg Institute (PGI-6) and JARA-FIT, 52425 Jülich, Germany.

ABSTRACT
Three-dimensional (3D) topological insulators are a new state of quantum matter, which exhibits both a bulk band structure with an insulating energy gap as well as metallic spin-polarized Dirac fermion states when interfaced with a topologically trivial material. There have been various attempts to tune the Dirac point to a desired energetic position for exploring its unusual quantum properties. Here we show a direct experimental proof by angle-resolved photoemission of the realization of a vertical topological p-n junction made of a heterostructure of two different binary 3D TI materials Bi2Te3 and Sb2Te3 epitaxially grown on Si(111). We demonstrate that the chemical potential is tunable by about 200 meV when decreasing the upper Sb2Te3 layer thickness from 25 to 6 quintuple layers without applying any external bias. These results make it realistic to observe the topological exciton condensate and pave the way for exploring other exotic quantum phenomena in the near future.

No MeSH data available.


Related in: MedlinePlus

High-resolution ARPES close to the Fermi level using hν=8.44 eV.(a,f,k) present the results obtained for the reference single Sb2Te3 film. For the heterostructures, the Sb2Te3 top layer thickness is marked on top. a–e depict the measured Fermi surface maps kx versus ky for EB=EF. The black dashed lines in the insets depict the hexagonal shape of the surface Brillouin zone. This symmetry character is also conserved for the shape of the surface state as one departs from the Dirac point. The white dashed lines (red line in the inset) indicate the cut direction where the corresponding normal emission spectra (f–j) were recorded. The Dirac point is marked by red arrows and the band structure calculations from DFT with adopted Fermi energy are superimposed in each spectrum. Again, red and blue dots here represent opposite in-plane spin polarization of the states. k–o show the respective momentum distribution curves at binding energies from EB=0.2 eV (bottom) to EB=EF=0 eV (top, marked by the red line) of the spectra above.
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f4: High-resolution ARPES close to the Fermi level using hν=8.44 eV.(a,f,k) present the results obtained for the reference single Sb2Te3 film. For the heterostructures, the Sb2Te3 top layer thickness is marked on top. a–e depict the measured Fermi surface maps kx versus ky for EB=EF. The black dashed lines in the insets depict the hexagonal shape of the surface Brillouin zone. This symmetry character is also conserved for the shape of the surface state as one departs from the Dirac point. The white dashed lines (red line in the inset) indicate the cut direction where the corresponding normal emission spectra (f–j) were recorded. The Dirac point is marked by red arrows and the band structure calculations from DFT with adopted Fermi energy are superimposed in each spectrum. Again, red and blue dots here represent opposite in-plane spin polarization of the states. k–o show the respective momentum distribution curves at binding energies from EB=0.2 eV (bottom) to EB=EF=0 eV (top, marked by the red line) of the spectra above.

Mentions: The surface electronic structure of the studied heterostructures was mapped in detail using high-resolution ARPES. Figure 3 displays long scale EB versus k// ARPES maps along trajectories traversing the -point of the surface Brillouin zone recorded with hν=21.22 eV. The exact cut directions in k-space were deduced by Fermi surface mapping and are highlighted in the insets of Fig. 4a–e. The plotted overview spectra all show dispersing bulk bands at relatively low background intensity, which signals the high-crystalline quality of the samples. Typical features of the Sb2Te3 band structure21 are revealed, such as the prominent Rashba-split surface state located between EB=0.4–0.8 eV and k//=±0.28 Å−1 in a spin-orbit induced gap within the projected band structure22. This feature is identified for all heterostructures. Furthermore, indications of the topologically protected Dirac cone states near the Fermi level are found in each spectrum. The photoemission cross-section for these states is small at 21.22 eV, however, they can be analysed in detail with lower photon energy (see next paragraph). An ab initio calculated electronic structure of a 6 QL-thick Sb2Te3 film along the corresponding crystallographic direction was superimposed on each spectrum to confirm the origin of the spectral features21.


Realization of a vertical topological p-n junction in epitaxial Sb2Te3/Bi2Te3 heterostructures.

Eschbach M, Młyńczak E, Kellner J, Kampmeier J, Lanius M, Neumann E, Weyrich C, Gehlmann M, Gospodarič P, Döring S, Mussler G, Demarina N, Luysberg M, Bihlmayer G, Schäpers T, Plucinski L, Blügel S, Morgenstern M, Schneider CM, Grützmacher D - Nat Commun (2015)

High-resolution ARPES close to the Fermi level using hν=8.44 eV.(a,f,k) present the results obtained for the reference single Sb2Te3 film. For the heterostructures, the Sb2Te3 top layer thickness is marked on top. a–e depict the measured Fermi surface maps kx versus ky for EB=EF. The black dashed lines in the insets depict the hexagonal shape of the surface Brillouin zone. This symmetry character is also conserved for the shape of the surface state as one departs from the Dirac point. The white dashed lines (red line in the inset) indicate the cut direction where the corresponding normal emission spectra (f–j) were recorded. The Dirac point is marked by red arrows and the band structure calculations from DFT with adopted Fermi energy are superimposed in each spectrum. Again, red and blue dots here represent opposite in-plane spin polarization of the states. k–o show the respective momentum distribution curves at binding energies from EB=0.2 eV (bottom) to EB=EF=0 eV (top, marked by the red line) of the spectra above.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4660041&req=5

f4: High-resolution ARPES close to the Fermi level using hν=8.44 eV.(a,f,k) present the results obtained for the reference single Sb2Te3 film. For the heterostructures, the Sb2Te3 top layer thickness is marked on top. a–e depict the measured Fermi surface maps kx versus ky for EB=EF. The black dashed lines in the insets depict the hexagonal shape of the surface Brillouin zone. This symmetry character is also conserved for the shape of the surface state as one departs from the Dirac point. The white dashed lines (red line in the inset) indicate the cut direction where the corresponding normal emission spectra (f–j) were recorded. The Dirac point is marked by red arrows and the band structure calculations from DFT with adopted Fermi energy are superimposed in each spectrum. Again, red and blue dots here represent opposite in-plane spin polarization of the states. k–o show the respective momentum distribution curves at binding energies from EB=0.2 eV (bottom) to EB=EF=0 eV (top, marked by the red line) of the spectra above.
Mentions: The surface electronic structure of the studied heterostructures was mapped in detail using high-resolution ARPES. Figure 3 displays long scale EB versus k// ARPES maps along trajectories traversing the -point of the surface Brillouin zone recorded with hν=21.22 eV. The exact cut directions in k-space were deduced by Fermi surface mapping and are highlighted in the insets of Fig. 4a–e. The plotted overview spectra all show dispersing bulk bands at relatively low background intensity, which signals the high-crystalline quality of the samples. Typical features of the Sb2Te3 band structure21 are revealed, such as the prominent Rashba-split surface state located between EB=0.4–0.8 eV and k//=±0.28 Å−1 in a spin-orbit induced gap within the projected band structure22. This feature is identified for all heterostructures. Furthermore, indications of the topologically protected Dirac cone states near the Fermi level are found in each spectrum. The photoemission cross-section for these states is small at 21.22 eV, however, they can be analysed in detail with lower photon energy (see next paragraph). An ab initio calculated electronic structure of a 6 QL-thick Sb2Te3 film along the corresponding crystallographic direction was superimposed on each spectrum to confirm the origin of the spectral features21.

Bottom Line: Three-dimensional (3D) topological insulators are a new state of quantum matter, which exhibits both a bulk band structure with an insulating energy gap as well as metallic spin-polarized Dirac fermion states when interfaced with a topologically trivial material.Here we show a direct experimental proof by angle-resolved photoemission of the realization of a vertical topological p-n junction made of a heterostructure of two different binary 3D TI materials Bi2Te3 and Sb2Te3 epitaxially grown on Si(111).We demonstrate that the chemical potential is tunable by about 200 meV when decreasing the upper Sb2Te3 layer thickness from 25 to 6 quintuple layers without applying any external bias.

View Article: PubMed Central - PubMed

Affiliation: Forschungszentrum Jülich GmbH, Peter Grünberg Institute (PGI-6) and JARA-FIT, 52425 Jülich, Germany.

ABSTRACT
Three-dimensional (3D) topological insulators are a new state of quantum matter, which exhibits both a bulk band structure with an insulating energy gap as well as metallic spin-polarized Dirac fermion states when interfaced with a topologically trivial material. There have been various attempts to tune the Dirac point to a desired energetic position for exploring its unusual quantum properties. Here we show a direct experimental proof by angle-resolved photoemission of the realization of a vertical topological p-n junction made of a heterostructure of two different binary 3D TI materials Bi2Te3 and Sb2Te3 epitaxially grown on Si(111). We demonstrate that the chemical potential is tunable by about 200 meV when decreasing the upper Sb2Te3 layer thickness from 25 to 6 quintuple layers without applying any external bias. These results make it realistic to observe the topological exciton condensate and pave the way for exploring other exotic quantum phenomena in the near future.

No MeSH data available.


Related in: MedlinePlus