Subcycle time-resolved THz-ARPES of topological surface currents in 2D momentum space
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Abstract
This dissertation investigates the ultrafast dynamics of lightwave-driven Dirac cur-
rents in the topologically protected surface state (TSS) of Bi2Te3 using angle-resolved
photoemission spectroscopy (ARPES) with subcycle temporal resolution and two-
dimensional (2D) momentum mapping. For this purpose, a new experimental setup
based on a high-repetition-rate laser system operating at 200 kHz was developed,
enabling the generation of few-cycle mid-infrared (MIR) pump pulses with stable
carrier-envelope phase that achieve peak electric field strengths in the MV/cm range
at the sample surface. Subcycle temporal resolution is enabled by an ultrashort 3-eV
two-photon photoemission (2PPE) probe with a pulse duration of less than 15 fs,
while 2D momentum mapping of the complete TSS electron population is enabled by
a custom hemispherical photoelectron analyzer. Using a driving frequency of 25 THz
with the electric-field polarization parallel to the sample surface and aligned along
the ΓK-direction of the Bi2Te3 surface Brillouin zone, the results demonstrate that
the field-driven electron dynamics within the TSS are governed by an interplay of
ballistic intraband acceleration and resonant interband excitation. The latter arises
from a resonance in the electronic band structure at the pump photon energy of
ħωMIR = 100 meV at a particular momentum along the ΓM direction. In contrast,
aligning the driving electric field along ΓM reveals that the momentum distribution
of intraband-accelerated electrons is strongly shaped by the hexagonal warping of the
Fermi surface. Due to the distinct phase relation of the two excitation mechanisms
with respect to the driving field, their interplay reduces both the phase shift and the
amplitude of the macroscopic surface current compared to purely ballistic transport,
while preserving the ballistic character of the intraband-accelerated charge carriers.
These findings demonstrate that the relative contributions of intraband and interband
processes can be controlled via the pump photon energy and polarization, highlight-
ing the potential for selective manipulation of lightwave-driven currents in topological
materials.
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Dates
Issued: 2026-03-06
Faculty
FB13:Physik
Language
en
Keywords
ARPESTHzTopological insulatorSubcycleTime-resolved ARPES
DFG-subjects
3.21-01 - Experimentelle Physik der kondensierten Materie
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Bergmeier, Tim: Subcycle time-resolved THz-ARPES of topological surface currents in 2D momentum space. : 2026-03-06. DOI: https://doi.org/10.17192/openumr/667.
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Except where otherwised noted, this item's license is described as Attribution-NonCommercial-NoDerivatives 4.0 International