Emergent Relativistic Effects in Condensed Matter
From Fundamental Aspects to Electronic Functionality

Selected Publications

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Ultrafast atomic-scale scanning tunnelling spectroscopy of a single vacancy in a monolayer crystal

C. Roelcke, L. Z. Kastner, M. Graml, A. Biereder, J. Wilhelm, J. Repp, R. Huber, Y.A. Gerasimenko

Nature Photonics

Defects in atomically thin semiconductors and their moiré heterostructures have emerged as a unique testbed
for quantum science. Strong light–matter coupling, large spin–orbit interaction and enhanced Coulomb
correlations facilitate a spin–photon interface for future qubit operations and efficient single-photon
quantum emitters. Yet, directly observing the relevant interplay of the electronic structure of a single defect
with other microscopic elementary excitations on their intrinsic length, time and energy scales remained a
long-held dream. Here we directly resolve in space, time and energy how a spin–orbit-split energy level of
an isolated selenium vacancy in a moiré-distorted WSe2 monolayer evolves under the controlled excitation
of lattice vibrations, using lightwave scanning tunnelling microscopy and spectroscopy. By locally launching
a phonon oscillation and taking ultrafast energy-resolved snapshots of the vacancy’s states faster than the
vibration period, we directly measure the impact of electron–phonon coupling in an isolated single-atom
defect. The combination of atomic spatial, sub-picosecond temporal and millielectronvolt energy resolution
marks a disruptive development towards a comprehensive understanding of complex quantum materials,
where the key microscopic elementary interactions can now be disentangled, one by one.
C. Roelcke, L. Z. Kastner, M. Graml, A. Biereder, J. Wilhelm, J. Repp, R. Huber, Y.A. Gerasimenko, Nat.
Photon. 59 (2024).


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