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Ultrafast electron dynamics at the Dirac node of the topological insulator Sb2Te3.

Zhu S, Ishida Y, Kuroda K, Sumida K, Ye M, Wang J, Pan H, Taniguchi M, Qiao S, Shin S, Kimura A - Sci Rep (2015)

Bottom Line: Sb2Te3 has an in-gap DP located completely above the Fermi energy (EF).The excited electrons in the upper Dirac cone stay longer than those below the DP to form an inverted population.This was attributed to a reduced density of states (DOS) near the DP.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.

ABSTRACT
Topological insulators (TIs) are a new quantum state of matter. Their surfaces and interfaces act as a topological boundary to generate massless Dirac fermions with spin-helical textures. Investigation of fermion dynamics near the Dirac point (DP) is crucial for the future development of spintronic devices incorporating topological insulators. However, research so far has been unsatisfactory because of a substantial overlap with the bulk valence band and a lack of a completely unoccupied DP. Here, we explore the surface Dirac fermion dynamics in the TI Sb2Te3 by time- and angle-resolved photoemission spectroscopy (TrARPES). Sb2Te3 has an in-gap DP located completely above the Fermi energy (EF). The excited electrons in the upper Dirac cone stay longer than those below the DP to form an inverted population. This was attributed to a reduced density of states (DOS) near the DP.

No MeSH data available.


Band structure of Sb2Te3 revealed into the unoccupied side.(a) The TrARPES images of Sb2Te3 recorded at t = 0.4 ps along the  direction. (b) Constant energy maps at 100, 290 and 410 meV.
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f1: Band structure of Sb2Te3 revealed into the unoccupied side.(a) The TrARPES images of Sb2Te3 recorded at t = 0.4 ps along the direction. (b) Constant energy maps at 100, 290 and 410 meV.

Mentions: By pumping the electrons into the unoccupied side, we observed a linear Dirac cone SS as shown in Fig. 1(a). Here, the pump-and-probe delay, t, was set to 0.4 ps. The DP is located ~180 meV above the EF and the Dirac velocity was estimated to be ~2.3 × 105 m/s. We found that both the upper and lower parts of the Dirac cone (UDC and LDC, respectively) were clearly visible above EF and they do not overlap with the bulk continuum states. Figure 1(b) shows the constant energy contours at 100, 290 and 410 meV with respect to the Fermi energy. With increasing the energy, the SS evolves from a circular to hexagonal shape. The isotropic constant surface can be observed both below and above the DP within the bulk energy gap. The hexagonal warping of the constant energy surfaces is quite small as long as bulk continuum states do not overlap with the SS. In the previous STM study on Sb2Te3, the DP is 80 meV higher, whereas the energy range of the SS (~120 meV above and below the DP) is consistent with the present observations3435; see Fig. 1(a). With such an ideal situation, there is a good opportunity to study the carrier dynamics of UDC and LDC separately, where interference from the bulk states is minimized.


Ultrafast electron dynamics at the Dirac node of the topological insulator Sb2Te3.

Zhu S, Ishida Y, Kuroda K, Sumida K, Ye M, Wang J, Pan H, Taniguchi M, Qiao S, Shin S, Kimura A - Sci Rep (2015)

Band structure of Sb2Te3 revealed into the unoccupied side.(a) The TrARPES images of Sb2Te3 recorded at t = 0.4 ps along the  direction. (b) Constant energy maps at 100, 290 and 410 meV.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4543953&req=5

f1: Band structure of Sb2Te3 revealed into the unoccupied side.(a) The TrARPES images of Sb2Te3 recorded at t = 0.4 ps along the direction. (b) Constant energy maps at 100, 290 and 410 meV.
Mentions: By pumping the electrons into the unoccupied side, we observed a linear Dirac cone SS as shown in Fig. 1(a). Here, the pump-and-probe delay, t, was set to 0.4 ps. The DP is located ~180 meV above the EF and the Dirac velocity was estimated to be ~2.3 × 105 m/s. We found that both the upper and lower parts of the Dirac cone (UDC and LDC, respectively) were clearly visible above EF and they do not overlap with the bulk continuum states. Figure 1(b) shows the constant energy contours at 100, 290 and 410 meV with respect to the Fermi energy. With increasing the energy, the SS evolves from a circular to hexagonal shape. The isotropic constant surface can be observed both below and above the DP within the bulk energy gap. The hexagonal warping of the constant energy surfaces is quite small as long as bulk continuum states do not overlap with the SS. In the previous STM study on Sb2Te3, the DP is 80 meV higher, whereas the energy range of the SS (~120 meV above and below the DP) is consistent with the present observations3435; see Fig. 1(a). With such an ideal situation, there is a good opportunity to study the carrier dynamics of UDC and LDC separately, where interference from the bulk states is minimized.

Bottom Line: Sb2Te3 has an in-gap DP located completely above the Fermi energy (EF).The excited electrons in the upper Dirac cone stay longer than those below the DP to form an inverted population.This was attributed to a reduced density of states (DOS) near the DP.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.

ABSTRACT
Topological insulators (TIs) are a new quantum state of matter. Their surfaces and interfaces act as a topological boundary to generate massless Dirac fermions with spin-helical textures. Investigation of fermion dynamics near the Dirac point (DP) is crucial for the future development of spintronic devices incorporating topological insulators. However, research so far has been unsatisfactory because of a substantial overlap with the bulk valence band and a lack of a completely unoccupied DP. Here, we explore the surface Dirac fermion dynamics in the TI Sb2Te3 by time- and angle-resolved photoemission spectroscopy (TrARPES). Sb2Te3 has an in-gap DP located completely above the Fermi energy (EF). The excited electrons in the upper Dirac cone stay longer than those below the DP to form an inverted population. This was attributed to a reduced density of states (DOS) near the DP.

No MeSH data available.