Phys. Rev. B 90, 235116 (2014) - Insights from angle-resolved photoemission spectroscopy on the metallic states of ${\mathrm{YbB}}_{6}(001):E(k)$ dispersion, temporal changes, and spatial variation

Insights from angle-resolved photoemission spectroscopy on the metallic states of ${YbB}_{6} (001) : E (k)$ dispersion, temporal changes, and spatial variation

E. Frantzeskakis, N. de Jong, J. X. Zhang, X. Zhang, Z. Li, C. L. Liang, Y. Wang, A. Varykhalov, Y. K. Huang, and M. S. Golden

Phys. Rev. B 90, 235116 – Published 8 December 2014

Abstract

We report high-resolution angle-resolved photoelectron spectroscopy (ARPES) results on the (001) cleavage surface of ${YbB}_{6}$ , a rare-earth compound that has been recently predicted to host surface electronic states with topological character. We observe two types of well-resolved metallic states, whose Fermi contours encircle the time-reversal invariant momenta of the ${YbB}_{6} (001)$ surface Brillouin zone, and whose full $E (k)$ dispersion relation can be measured wholly unmasked by states from the rest of the electronic structure. Although the two-dimensional character of these metallic states is confirmed by their lack of out-of-plane dispersion, our work reveals two aspects which were not observed in previous experiments. First, these states do not resemble two branches of opposite, linear velocity that cross at a Dirac point, but rather straightforward parabolas that terminate to high binding energy with a clear band bottom. Secondly, these states are sensitive to time-dependent changes of the ${YbB}_{6}$ surface under ultrahigh-vacuum conditions. Adding the fact that these data from cleaved ${YbB}_{6}$ surfaces also display spatial variations in the electronic structure, it appears there is little in common between the theoretical expectations for an idealized ${YbB}_{6} (001)$ crystal truncation on the one hand, and these ARPES data from real cleavage surfaces on the other.

Received 10 September 2014
Revised 21 November 2014

DOI:https://doi.org/10.1103/PhysRevB.90.235116

Authors & Affiliations

E. Frantzeskakis^1,*, N. de Jong¹, J. X. Zhang^2,3, X. Zhang², Z. Li³, C. L. Liang², Y. Wang², A. Varykhalov⁴, Y. K. Huang¹, and M. S. Golden^1,†

¹Institute of Physics (IoP), University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands
²Department of Materials Science and Engineering, Beijing University of Technology, Pingleyuan 100, Chaoyang Districts, Beijing 100124, China
³Department of Materials Science and Engineering, Hefei University of Technology, Tunxi Road 193, Anhui, Hefei 230009, China
⁴Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, 12489 Berlin, Germany

^*e.frantzeskakis@uva.nl
^†m.s.golden@uva.nl

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 90, Iss. 23 — 15 December 2014

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) Electronic band structure of ${YbB}_{6}$ (001) along the $\bar{X Γ X}$ direction of the surface Brillouin zone. The nondispersive feature at $\sim 1.1$ eV corresponds to the lowest binding energy Yb $4 f$ states. Electron pockets are observed at $\bar{Γ}$ and $\bar{X}$ . (b) Zoom of the electronic states near $E_{F}$ at $\bar{Γ}$ . (c) Zoom of the electronic states near $E_{F}$ at $\bar{X}$ . (d) Same as panel (b), but acquired in the second SBZ, where favorable photoemission matrix elements give clear access to the band minimum. A second electron pocket is also observed. (e) Energy distribution curve for $k$ around $\bar{Γ}$ , taken by integrating the area denoted by the red arrow in panel (d), which is well inside the $k_{F}$ values for the larger electron pocket. All data in this figure were acquired using an excitation energy of 35 eV at a sample temperature of 37 K.
Reuse & Permissions
Figure 2
(a) $E (k)$ dispersion of the states at $\bar{X}$ along $\bar{X Γ X}$ acquired with $h ν = 70$ eV. (b)–(d) In-plane constant energy contours: $(k_{x}, k_{y})$ momentum distribution of the electron pockets centered at $\bar{X}$ (b) at the Fermi level, (c) at a binding energy of 20 meV, and (d) at a binding energy of 100 meV. (e) Out-of-plane constant energy contours: $(k_{x}, k_{z})$ momentum distribution of the electron pockets centered at $\bar{X}$ at a binding energy of 20 meV. Data in panels (a)–(d) have been acquired using an excitation energy of 70 eV. Panel (e) is based upon data recorded with photon energies between 62 and 78 eV. In all cases, the sample temperature was 37 K.
Reuse & Permissions
Figure 3
(a) The Fermi surface of ${YbB}_{6}$ (001). Clear elliptical (circular) contours are seen to close around the $\bar{Γ} (\bar{X})$ points. Data have been acquired by sequential scanning of horizontal $k$ -slices using an angular step of 0. $5^{o}$ . The time since sample cleavage is shown on the left for the first and last $k$ -slice The excitation energy was 35 eV and the gray scale shows the ARPES intensity integrated $\pm 5$ meV around the Fermi energy. Note the clear reduction in the size of the constant energy contours during the course of the measurement (from the bottom to the top). The red, solid lines denote the borders of the first surface Brillouin zone. (b) $E (k)$ dispersion along the $k$ -path indicated in (a) as a green dotted line. Arrows highlight that the electron pocket at positive $k$ -values (acquired toward the end of the sequential scanning) has a shallower minimum than that at negative $k$ -values (acquired toward the beginning). (c) Upward shift of the binding energy of the electron pocket centered on $\bar{X}$ as the time since sample cleavage increases. For all data, the excitation energy was 70 eV and the sample was held at 37 K.
Reuse & Permissions
Figure 4
(a) Angle-integrated ARPES intensity along $\bar{X Γ X}$ , showing the time evolution of the Yb $4 f$ states closest to $E_{F}$ . The inset compares the double-peak line shape of the Yb $4 f$ states measured on a fresh cleave (purple) with the line shape measured after exposure to UHV (black). “S” and “B” denote the surface- and bulk-derived components of the higher-binding-energy feature, respectively. The time labels given refer to the time after cleavage. (b) Spatial variations in the binding energy of the Yb $4 f$ states (data acquired 240 min after cleavage). Regions 1 and 2 are situated $100 μ m$ away from each other. (c),(d) Valence-band data acquired from regions 1 and 2. To enhance the contribution from the dispersive features in panels (c) and (d), the data are normalized to have equal total intensity for each horizontal, momentum distribution slice. (e) Raw data in the $E (k$ ) region of highlighted in panel (d) by the dashed rectangle. The arrow points out the holelike feature that dominates the near- $E_{F}$ electronic structure of ${YbB}_{6}$ (001) 240 min after cleavage. The data of panel (a) were acquired with $h ν = 70$ eV, and (b)–(e) with $h ν = 150$ eV. The sample temperature was 37 K for all data shown.
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Insights from angle-resolved photoemission spectroscopy on the metallic states of ${YbB}_{6} (001) : E (k)$ dispersion, temporal changes, and spatial variation

E. Frantzeskakis, N. de Jong, J. X. Zhang, X. Zhang, Z. Li, C. L. Liang, Y. Wang, A. Varykhalov, Y. K. Huang, and M. S. Golden

Phys. Rev. B 90, 235116 – Published 8 December 2014

Abstract

Authors & Affiliations

Article Text (Subscription Required)

References (Subscription Required)

Issue

Access Options

Physical Review B

covering condensed matter and materials physics

Insights from angle-resolved photoemission spectroscopy on the metallic states of YbB6(001):E(k) dispersion, temporal changes, and spatial variation

E. Frantzeskakis, N. de Jong, J. X. Zhang, X. Zhang, Z. Li, C. L. Liang, Y. Wang, A. Varykhalov, Y. K. Huang, and M. S. Golden

Phys. Rev. B 90, 235116 – Published 8 December 2014

Abstract

Authors & Affiliations

Article Text (Subscription Required)

References (Subscription Required)

Issue

Access Options

Authorization Required

Other Options

Download & Share

Images

Figure 1

Figure 2

Figure 3

Figure 4

Log In

Search

Article Lookup

Paste a citation or DOI

Enter a citation

Insights from angle-resolved photoemission spectroscopy on the metallic states of ${YbB}_{6} (001) : E (k)$ dispersion, temporal changes, and spatial variation