Limits...
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.


Related in: MedlinePlus

TrARPES of Sb2Te3.(a) TrARPES images recorded along the  line recorded before pump (left; images recorded at ≤0.6 ps were averaged), at 0 ps (middle), and their difference (right panel). The frames A to I span in the angular range of ±15 degrees and in the energy ranges of [0.80, 0.90], [0.70, 0.76], [0.60, 0.66], [0.50, 0.56], [0.40, 0.46], [0.30, 0.36], [0.20, 0.26], [0.06, 0.17] and [0.01, 0.05] (in units of eV), respectively. (b) Intensity variation line profiles. Integrated intensity in each of the frames A to I is plotted as functions of delay time in a linear (upper panel) and in a logarithmic scale (lower panel). (c) TrARPES images. Upper and lower panels show TrARPES and difference to that recorded before pump. Full set of TrARPES and difference images are provided as a Supplementary Movie S1. (d) EDCs (integration of TrARPES images over ± 15 degrees) recorded at 0 ≤ t ≤ 1.00 ps (left), 1.00 ≤ t ≤ 2.97 ps (middle), and at 2.97 ≤ t ≤ 5.13 ps (right panel). Here, the EDCs are normalized to the area around the peak in the LDC region. For the full set of EDCs, see Supplementary Movie S2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4543953&req=5

f2: TrARPES of Sb2Te3.(a) TrARPES images recorded along the line recorded before pump (left; images recorded at ≤0.6 ps were averaged), at 0 ps (middle), and their difference (right panel). The frames A to I span in the angular range of ±15 degrees and in the energy ranges of [0.80, 0.90], [0.70, 0.76], [0.60, 0.66], [0.50, 0.56], [0.40, 0.46], [0.30, 0.36], [0.20, 0.26], [0.06, 0.17] and [0.01, 0.05] (in units of eV), respectively. (b) Intensity variation line profiles. Integrated intensity in each of the frames A to I is plotted as functions of delay time in a linear (upper panel) and in a logarithmic scale (lower panel). (c) TrARPES images. Upper and lower panels show TrARPES and difference to that recorded before pump. Full set of TrARPES and difference images are provided as a Supplementary Movie S1. (d) EDCs (integration of TrARPES images over ± 15 degrees) recorded at 0 ≤ t ≤ 1.00 ps (left), 1.00 ≤ t ≤ 2.97 ps (middle), and at 2.97 ≤ t ≤ 5.13 ps (right panel). Here, the EDCs are normalized to the area around the peak in the LDC region. For the full set of EDCs, see Supplementary Movie S2.

Mentions: To study the pump-induced dynamics of the surface Dirac fermions, we altered the pump and probe delay and investigated the time dependent variations in the TrARPES images. Figure 2(a) shows the difference image along the line measured at t = 0.4 ps. Both the Dirac cone SS and unoccupied bulk state were clearly observed. To show the energy dependent dynamics, we set energy and momentum frames [A to I: see Fig. 2(a)] and plotted the intensity variation in each frame as functions of t [see Fig. 2(b)]. Also, to show the variation in the different bands more clearly, we show the original and difference images for typical delay times in Fig. 2(c) and in a Supplementary Movie S1. Here we note that the intensity variation line profiles of bulk and surface states at the same energy overlapped each other as shown in the Supplementary Fig. S1.


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)

TrARPES of Sb2Te3.(a) TrARPES images recorded along the  line recorded before pump (left; images recorded at ≤0.6 ps were averaged), at 0 ps (middle), and their difference (right panel). The frames A to I span in the angular range of ±15 degrees and in the energy ranges of [0.80, 0.90], [0.70, 0.76], [0.60, 0.66], [0.50, 0.56], [0.40, 0.46], [0.30, 0.36], [0.20, 0.26], [0.06, 0.17] and [0.01, 0.05] (in units of eV), respectively. (b) Intensity variation line profiles. Integrated intensity in each of the frames A to I is plotted as functions of delay time in a linear (upper panel) and in a logarithmic scale (lower panel). (c) TrARPES images. Upper and lower panels show TrARPES and difference to that recorded before pump. Full set of TrARPES and difference images are provided as a Supplementary Movie S1. (d) EDCs (integration of TrARPES images over ± 15 degrees) recorded at 0 ≤ t ≤ 1.00 ps (left), 1.00 ≤ t ≤ 2.97 ps (middle), and at 2.97 ≤ t ≤ 5.13 ps (right panel). Here, the EDCs are normalized to the area around the peak in the LDC region. For the full set of EDCs, see Supplementary Movie S2.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: TrARPES of Sb2Te3.(a) TrARPES images recorded along the line recorded before pump (left; images recorded at ≤0.6 ps were averaged), at 0 ps (middle), and their difference (right panel). The frames A to I span in the angular range of ±15 degrees and in the energy ranges of [0.80, 0.90], [0.70, 0.76], [0.60, 0.66], [0.50, 0.56], [0.40, 0.46], [0.30, 0.36], [0.20, 0.26], [0.06, 0.17] and [0.01, 0.05] (in units of eV), respectively. (b) Intensity variation line profiles. Integrated intensity in each of the frames A to I is plotted as functions of delay time in a linear (upper panel) and in a logarithmic scale (lower panel). (c) TrARPES images. Upper and lower panels show TrARPES and difference to that recorded before pump. Full set of TrARPES and difference images are provided as a Supplementary Movie S1. (d) EDCs (integration of TrARPES images over ± 15 degrees) recorded at 0 ≤ t ≤ 1.00 ps (left), 1.00 ≤ t ≤ 2.97 ps (middle), and at 2.97 ≤ t ≤ 5.13 ps (right panel). Here, the EDCs are normalized to the area around the peak in the LDC region. For the full set of EDCs, see Supplementary Movie S2.
Mentions: To study the pump-induced dynamics of the surface Dirac fermions, we altered the pump and probe delay and investigated the time dependent variations in the TrARPES images. Figure 2(a) shows the difference image along the line measured at t = 0.4 ps. Both the Dirac cone SS and unoccupied bulk state were clearly observed. To show the energy dependent dynamics, we set energy and momentum frames [A to I: see Fig. 2(a)] and plotted the intensity variation in each frame as functions of t [see Fig. 2(b)]. Also, to show the variation in the different bands more clearly, we show the original and difference images for typical delay times in Fig. 2(c) and in a Supplementary Movie S1. Here we note that the intensity variation line profiles of bulk and surface states at the same energy overlapped each other as shown in the Supplementary Fig. S1.

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.


Related in: MedlinePlus