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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

Valence band structure and low-energy dispersive states of YbB6.(a) Photoemission intensity plot showing the valence band structure of YbB6. The flat 4f bands are marked by the arrows. Data were taken along cut 1 of S1 at 6 K with 33 eV photons in SSRL. (b) Left: photoemission intensity map at EF taken with 31 eV photons at 6 K in SSRL. The intensity was integrated over a window of [EF - 10 meV, EF + 10 meV]. Right: the momentum cuts along which data were taken are marked in the projected two-dimensional BZ. (c) Top: the photoemission intensity plot along cut 2 taken on S2 with 91 eV photons at 18 K in SLS. Bottom: the same data after subtracting a momentum-independent background. The spectra far away from the dispersive region show no momentum dependence and thus taken as the background. The white lines indicate the α and γ bands, the dashed line is extrapolated from the linear dispersion. The red dashed line indicates the overlap of the band bottom of α and band top of γ. (d) The corresponding MDCs along cut 2 within [EF - 400 meV, EF - 150 meV]. The red line is the dispersion tracked from the MDC peaks and the red dashed line is extrapolated from the linear dispersion. (e) The photoemission intensity plot on S2 along cut 3 and cut 4 measured with 70 eV photons at 18 K in SLS. (f, g) The corresponding MDCs along cut 3 and cut 4 in panel (e), respectively. The red dashed lines are the dispersions of the β bands. The highlighted MDC in red indicates the possible energy position of the Dirac points. (h, i) The photoemission intensity plot on S3 along cut 5 and its corresponding energy distribution curves (EDCs) taken with 47 eV photons at 20 K in KEK, showing an additional δ band. (j) A schematic of all the bands observed along  direction.
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f2: Valence band structure and low-energy dispersive states of YbB6.(a) Photoemission intensity plot showing the valence band structure of YbB6. The flat 4f bands are marked by the arrows. Data were taken along cut 1 of S1 at 6 K with 33 eV photons in SSRL. (b) Left: photoemission intensity map at EF taken with 31 eV photons at 6 K in SSRL. The intensity was integrated over a window of [EF - 10 meV, EF + 10 meV]. Right: the momentum cuts along which data were taken are marked in the projected two-dimensional BZ. (c) Top: the photoemission intensity plot along cut 2 taken on S2 with 91 eV photons at 18 K in SLS. Bottom: the same data after subtracting a momentum-independent background. The spectra far away from the dispersive region show no momentum dependence and thus taken as the background. The white lines indicate the α and γ bands, the dashed line is extrapolated from the linear dispersion. The red dashed line indicates the overlap of the band bottom of α and band top of γ. (d) The corresponding MDCs along cut 2 within [EF - 400 meV, EF - 150 meV]. The red line is the dispersion tracked from the MDC peaks and the red dashed line is extrapolated from the linear dispersion. (e) The photoemission intensity plot on S2 along cut 3 and cut 4 measured with 70 eV photons at 18 K in SLS. (f, g) The corresponding MDCs along cut 3 and cut 4 in panel (e), respectively. The red dashed lines are the dispersions of the β bands. The highlighted MDC in red indicates the possible energy position of the Dirac points. (h, i) The photoemission intensity plot on S3 along cut 5 and its corresponding energy distribution curves (EDCs) taken with 47 eV photons at 20 K in KEK, showing an additional δ band. (j) A schematic of all the bands observed along direction.

Mentions: Figure 2(a) shows the photoemission intensity of YbB6 on sample 1 (S1) over a large energy scale, the non-dispersive Yb 4f bands are located at around 1 eV and 2.3 eV below Fermi energy (EF). They correspond to the 2F7/2 and 2F5/2 multiplets of the Yb2+ 4f14→4f13 final states based on the LDA calculation20. The energy difference between the two multiplets is 1.3 eV, consistent with the calculation. However, the energy positions of these 4f bands are deeper than that calculated in Ref. 20, suggesting correlation effects need to be reconsidered in calculation. In addition, some dispersive features are resolved in the low energy range, which may mostly originate from the Yb 5d orbitals20.


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)

Valence band structure and low-energy dispersive states of YbB6.(a) Photoemission intensity plot showing the valence band structure of YbB6. The flat 4f bands are marked by the arrows. Data were taken along cut 1 of S1 at 6 K with 33 eV photons in SSRL. (b) Left: photoemission intensity map at EF taken with 31 eV photons at 6 K in SSRL. The intensity was integrated over a window of [EF - 10 meV, EF + 10 meV]. Right: the momentum cuts along which data were taken are marked in the projected two-dimensional BZ. (c) Top: the photoemission intensity plot along cut 2 taken on S2 with 91 eV photons at 18 K in SLS. Bottom: the same data after subtracting a momentum-independent background. The spectra far away from the dispersive region show no momentum dependence and thus taken as the background. The white lines indicate the α and γ bands, the dashed line is extrapolated from the linear dispersion. The red dashed line indicates the overlap of the band bottom of α and band top of γ. (d) The corresponding MDCs along cut 2 within [EF - 400 meV, EF - 150 meV]. The red line is the dispersion tracked from the MDC peaks and the red dashed line is extrapolated from the linear dispersion. (e) The photoemission intensity plot on S2 along cut 3 and cut 4 measured with 70 eV photons at 18 K in SLS. (f, g) The corresponding MDCs along cut 3 and cut 4 in panel (e), respectively. The red dashed lines are the dispersions of the β bands. The highlighted MDC in red indicates the possible energy position of the Dirac points. (h, i) The photoemission intensity plot on S3 along cut 5 and its corresponding energy distribution curves (EDCs) taken with 47 eV photons at 20 K in KEK, showing an additional δ band. (j) A schematic of all the bands observed along  direction.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Valence band structure and low-energy dispersive states of YbB6.(a) Photoemission intensity plot showing the valence band structure of YbB6. The flat 4f bands are marked by the arrows. Data were taken along cut 1 of S1 at 6 K with 33 eV photons in SSRL. (b) Left: photoemission intensity map at EF taken with 31 eV photons at 6 K in SSRL. The intensity was integrated over a window of [EF - 10 meV, EF + 10 meV]. Right: the momentum cuts along which data were taken are marked in the projected two-dimensional BZ. (c) Top: the photoemission intensity plot along cut 2 taken on S2 with 91 eV photons at 18 K in SLS. Bottom: the same data after subtracting a momentum-independent background. The spectra far away from the dispersive region show no momentum dependence and thus taken as the background. The white lines indicate the α and γ bands, the dashed line is extrapolated from the linear dispersion. The red dashed line indicates the overlap of the band bottom of α and band top of γ. (d) The corresponding MDCs along cut 2 within [EF - 400 meV, EF - 150 meV]. The red line is the dispersion tracked from the MDC peaks and the red dashed line is extrapolated from the linear dispersion. (e) The photoemission intensity plot on S2 along cut 3 and cut 4 measured with 70 eV photons at 18 K in SLS. (f, g) The corresponding MDCs along cut 3 and cut 4 in panel (e), respectively. The red dashed lines are the dispersions of the β bands. The highlighted MDC in red indicates the possible energy position of the Dirac points. (h, i) The photoemission intensity plot on S3 along cut 5 and its corresponding energy distribution curves (EDCs) taken with 47 eV photons at 20 K in KEK, showing an additional δ band. (j) A schematic of all the bands observed along direction.
Mentions: Figure 2(a) shows the photoemission intensity of YbB6 on sample 1 (S1) over a large energy scale, the non-dispersive Yb 4f bands are located at around 1 eV and 2.3 eV below Fermi energy (EF). They correspond to the 2F7/2 and 2F5/2 multiplets of the Yb2+ 4f14→4f13 final states based on the LDA calculation20. The energy difference between the two multiplets is 1.3 eV, consistent with the calculation. However, the energy positions of these 4f bands are deeper than that calculated in Ref. 20, suggesting correlation effects need to be reconsidered in calculation. In addition, some dispersive features are resolved in the low energy range, which may mostly originate from the Yb 5d orbitals20.

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