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Angle-resolved photoemission spectroscopy study on the surface states of the correlated topological insulator YbB6.

Xia M, Jiang J, Ye ZR, Wang YH, Zhang Y, Chen SD, Niu XH, Xu DF, Chen F, Chen XH, Xie BP, Zhang T, Feng DL - Sci Rep (2014)

Bottom Line: Circular dichroism photoemission spectra suggest that these in-gap states possess chirality of orbital angular momentum, which is related to the chiral spin texture, further indicative of their topological nature.The observed insulating gap of YbB6 is about 100 meV, larger than that found by theoretical calculations.Our results present strong evidence that YbB6 is a correlated topological insulator and provide a foundation for further studies of this promising material.

View Article: PubMed Central - PubMed

Affiliation: 1] State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, China [2].

ABSTRACT
YbB6 is recently predicted to be a moderately correlated topological insulator, which provides a playground to explore the interplay between correlation and topological properties. With angle-resolved photoemission spectroscopy, we directly observed almost linearly dispersive bands around the time-reversal invariant momenta and with negligible kz dependence, consistent with odd number of surface states crossing the Fermi level in a Z2 topological insulator. Circular dichroism photoemission spectra suggest that these in-gap states possess chirality of orbital angular momentum, which is related to the chiral spin texture, further indicative of their topological nature. The observed insulating gap of YbB6 is about 100 meV, larger than that found by theoretical calculations. Our results present strong evidence that YbB6 is a correlated topological insulator and provide a foundation for further studies of this promising material.

No MeSH data available.


Related in: MedlinePlus

Hole-like surface in YbB6 and temperature dependent electronic structure of electron-like surface in YbB6.(a) Left: Photoemission intensity map of S6 with hole-like pockets. The intensity was integrated over a window of [EF - 10 meV, EF + 10 meV]. Right: the momentum cuts along which the data were taken are marked in the projected two-dimensional BZ. (b, c) Two photoemission intensity plots taken along cut 6 and cut 7 indicated in panel (a) by the blue arrows, respectively. The hole-like dispersions are indicated by the dashed lines. Data were taken on S6 at 20 K with 47 eV photons in KEK. (d) A schematic plot to show the chemical potential shift in different surfaces and the integrated EDCs of the two different surface to compare the different chemical potential. μ2 and μ6 refer to the chemical potential of the two different cleaved surfaces of S2 and S6. (e) The photoemission intensity data taken along  direction at 6 K and 196 K, respectively. Data were taken on S1 at SSRL with 31 eV photons.
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f5: Hole-like surface in YbB6 and temperature dependent electronic structure of electron-like surface in YbB6.(a) Left: Photoemission intensity map of S6 with hole-like pockets. The intensity was integrated over a window of [EF - 10 meV, EF + 10 meV]. Right: the momentum cuts along which the data were taken are marked in the projected two-dimensional BZ. (b, c) Two photoemission intensity plots taken along cut 6 and cut 7 indicated in panel (a) by the blue arrows, respectively. The hole-like dispersions are indicated by the dashed lines. Data were taken on S6 at 20 K with 47 eV photons in KEK. (d) A schematic plot to show the chemical potential shift in different surfaces and the integrated EDCs of the two different surface to compare the different chemical potential. μ2 and μ6 refer to the chemical potential of the two different cleaved surfaces of S2 and S6. (e) The photoemission intensity data taken along direction at 6 K and 196 K, respectively. Data were taken on S1 at SSRL with 31 eV photons.

Mentions: We found that the chemical potential varies during different samples. In most cases the variation is within 100 meV and the band structure is similar as discussed above. But sometimes, we observed very different, hole-like pocket around , referred to as β' in Figs. 5(a) –5(c). The electron-like Fermi pocket and the hole-like Fermi pocket can be even observed in different regions of the same sample, which may be due to inhomogeneous doping of the sample or different surface conditions. The chemical potential of the sample with hole-like pockets (S6) differs 490 meV from that of S2 with electron-like pockets, indicated by the shift of the 4f bands between these two samples shown in Fig. 5(d). Since the linear extrapolation of β' in S6 leads to a crossing at around 180 meV above EF and the crossing point of β is located at around 320 meV below EF, the energy position of the crossing point shifted about 500 meV. This is consistent with the 490 meV shift of the 4f bands within error bar, indicating that β' could be the lower half of the possible Dirac cone of β. The slope of β near its crossing point and the slope of β' are nearly same with only 4% difference, further support they are from one Dirac cone. Around , on the other hand, we did not resolve the band below the crossing of α, which could be concealed by the bulk band γ.


Angle-resolved photoemission spectroscopy study on the surface states of the correlated topological insulator YbB6.

Xia M, Jiang J, Ye ZR, Wang YH, Zhang Y, Chen SD, Niu XH, Xu DF, Chen F, Chen XH, Xie BP, Zhang T, Feng DL - Sci Rep (2014)

Hole-like surface in YbB6 and temperature dependent electronic structure of electron-like surface in YbB6.(a) Left: Photoemission intensity map of S6 with hole-like pockets. The intensity was integrated over a window of [EF - 10 meV, EF + 10 meV]. Right: the momentum cuts along which the data were taken are marked in the projected two-dimensional BZ. (b, c) Two photoemission intensity plots taken along cut 6 and cut 7 indicated in panel (a) by the blue arrows, respectively. The hole-like dispersions are indicated by the dashed lines. Data were taken on S6 at 20 K with 47 eV photons in KEK. (d) A schematic plot to show the chemical potential shift in different surfaces and the integrated EDCs of the two different surface to compare the different chemical potential. μ2 and μ6 refer to the chemical potential of the two different cleaved surfaces of S2 and S6. (e) The photoemission intensity data taken along  direction at 6 K and 196 K, respectively. Data were taken on S1 at SSRL with 31 eV photons.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126005&req=5

f5: Hole-like surface in YbB6 and temperature dependent electronic structure of electron-like surface in YbB6.(a) Left: Photoemission intensity map of S6 with hole-like pockets. The intensity was integrated over a window of [EF - 10 meV, EF + 10 meV]. Right: the momentum cuts along which the data were taken are marked in the projected two-dimensional BZ. (b, c) Two photoemission intensity plots taken along cut 6 and cut 7 indicated in panel (a) by the blue arrows, respectively. The hole-like dispersions are indicated by the dashed lines. Data were taken on S6 at 20 K with 47 eV photons in KEK. (d) A schematic plot to show the chemical potential shift in different surfaces and the integrated EDCs of the two different surface to compare the different chemical potential. μ2 and μ6 refer to the chemical potential of the two different cleaved surfaces of S2 and S6. (e) The photoemission intensity data taken along direction at 6 K and 196 K, respectively. Data were taken on S1 at SSRL with 31 eV photons.
Mentions: We found that the chemical potential varies during different samples. In most cases the variation is within 100 meV and the band structure is similar as discussed above. But sometimes, we observed very different, hole-like pocket around , referred to as β' in Figs. 5(a) –5(c). The electron-like Fermi pocket and the hole-like Fermi pocket can be even observed in different regions of the same sample, which may be due to inhomogeneous doping of the sample or different surface conditions. The chemical potential of the sample with hole-like pockets (S6) differs 490 meV from that of S2 with electron-like pockets, indicated by the shift of the 4f bands between these two samples shown in Fig. 5(d). Since the linear extrapolation of β' in S6 leads to a crossing at around 180 meV above EF and the crossing point of β is located at around 320 meV below EF, the energy position of the crossing point shifted about 500 meV. This is consistent with the 490 meV shift of the 4f bands within error bar, indicating that β' could be the lower half of the possible Dirac cone of β. The slope of β near its crossing point and the slope of β' are nearly same with only 4% difference, further support they are from one Dirac cone. Around , on the other hand, we did not resolve the band below the crossing of α, which could be concealed by the bulk band γ.

Bottom Line: Circular dichroism photoemission spectra suggest that these in-gap states possess chirality of orbital angular momentum, which is related to the chiral spin texture, further indicative of their topological nature.The observed insulating gap of YbB6 is about 100 meV, larger than that found by theoretical calculations.Our results present strong evidence that YbB6 is a correlated topological insulator and provide a foundation for further studies of this promising material.

View Article: PubMed Central - PubMed

Affiliation: 1] State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, China [2].

ABSTRACT
YbB6 is recently predicted to be a moderately correlated topological insulator, which provides a playground to explore the interplay between correlation and topological properties. With angle-resolved photoemission spectroscopy, we directly observed almost linearly dispersive bands around the time-reversal invariant momenta and with negligible kz dependence, consistent with odd number of surface states crossing the Fermi level in a Z2 topological insulator. Circular dichroism photoemission spectra suggest that these in-gap states possess chirality of orbital angular momentum, which is related to the chiral spin texture, further indicative of their topological nature. The observed insulating gap of YbB6 is about 100 meV, larger than that found by theoretical calculations. Our results present strong evidence that YbB6 is a correlated topological insulator and provide a foundation for further studies of this promising material.

No MeSH data available.


Related in: MedlinePlus