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Tip-Induced Dissociation of Diethyl Ether on Si(001)─Influence of Molecular Structure on Final Reaction Products
No full textDirect visualization of hybrid excitons in van der Waals heterostructures
Full text linkVan der Waals heterostructures show fascinating physics including trapped
moire exciton states, anomalous moire exciton transport, generalized Wigner
crystals, etc. Bilayers of transition metal dichalcogenides (TMDs) are
characterized by long-lived spatially separated interlayer excitons. Provided a
strong interlayer tunneling, hybrid exciton states consisting of interlayer and
intralayer excitons can be formed. Here, electrons and/or holes are in a
superposition of both layers. Although crucial for optics, dynamics, and
transport, hybrid excitons are usually optically inactive and have therefore
not been directly observed yet. Based on a microscopic and material-specific
theory, we show that time- and angle-resolved photoemission spectroscopy
(tr-ARPES) is the ideal technique to directly visualize these hybrid excitons.
Concretely, we predict a characteristic double-peak ARPES signal arising from
the hybridized hole in the MoS homobilayer. The relative intensity is
proportional to the quantum mixture of the two hybrid valence bands at the
point. Due to the strong hybridization, the peak separation of more
than 0.5 eV can be resolved in ARPES experiments. Our study provides a concrete
recipe of how to directly visualize hybrid excitons and how to distinguish them
from the usually observed regular excitonic signatures
Probing excitons with time-resolved momentum microscopy
No full textExcitons -- two-particle correlated electron-hole pairs -- are the dominant
low-energy optical excitation in the broad class of semiconductor materials,
which range from classical silicon to perovskites, and from two-dimensional to
organic materials. Recently, the study of excitons has been brought on a new
level of detail by the application of photoemission momentum microscopy -- a
technique that has dramatically extended the experimental capabilities of time-
and angle-resolved photoemission spectroscopy (trARPES). Here, we review how
the energy- and momentum-resolved photoelectron detection scheme enables direct
access to the energy landscape of bright and dark excitons, and, more
generally, to the momentum-coordinate of the exciton that is fundamental to its
wavefunction. Focusing on two-dimensional materials and organic semiconductors
as two tuneable platforms for exciton physics, we first discuss the typical
photoemission fingerprint of excitons in momentum microscopy and highlight that
is is possible to obtain information not only on the electron- but also
hole-component of the former exciton. Second, we focus on the recent
application of photoemission orbital tomography to such excitons, and discuss
how this provides a unique access to the real-space properties of the exciton
wavefunction. Throughout the review, we detail how studies performed on
two-dimensional transition metal dichalcogenides and organic semiconductors
lead to very similar conclusions, and, in this manner, highlight the strength
of time-resolved momentum microscopy for the study of optical excitations in
semiconductors
Probing excitons with time-resolved momentum microscopy
No full textExcitons -- two-particle correlated electron-hole pairs -- are the dominant
low-energy optical excitation in the broad class of semiconductor materials,
which range from classical silicon to perovskites, and from two-dimensional to
organic materials. Recently, the study of excitons has been brought on a new
level of detail by the application of photoemission momentum microscopy -- a
technique that has dramatically extended the experimental capabilities of time-
and angle-resolved photoemission spectroscopy (trARPES). Here, we review how
the energy- and momentum-resolved photoelectron detection scheme enables direct
access to the energy landscape of bright and dark excitons, and, more
generally, to the momentum-coordinate of the exciton that is fundamental to its
wavefunction. Focusing on two-dimensional materials and organic semiconductors
as two tuneable platforms for exciton physics, we first discuss the typical
photoemission fingerprint of excitons in momentum microscopy and highlight that
is is possible to obtain information not only on the electron- but also
hole-component of the former exciton. Second, we focus on the recent
application of photoemission orbital tomography to such excitons, and discuss
how this provides a unique access to the real-space properties of the exciton
wavefunction. Throughout the review, we detail how studies performed on
two-dimensional transition metal dichalcogenides and organic semiconductors
lead to very similar conclusions, and, in this manner, highlight the strength
of time-resolved momentum microscopy for the study of optical excitations in
semiconductors
Coherent multidimensional photoelectron spectroscopy of ultrafast quasiparticle dressing by light
No full textProbing excitons with time-resolved momentum microscopy
No full textExcitons – two-particle correlated electron-hole pairs – are the dominant low-energy optical excitation in the broad class of semiconductor materials, which range from classical silicon to perovskites, and from two-dimensional to organic materials. The study of excitons has been brought on a new level of detail by the application of photoemission momentum microscopy – a technique that has dramatically extended the capabilities of time- and angle resolved photoemission spectroscopy. Here, we review how the photoelectron detection scheme enables direct access to the energy landscape of bright and dark excitons, and, more generally, to the momentum-coordinate of the exciton wavefunction. Focusing on two-dimensional materials and organic semiconductors, we first discuss the typical photoemission fingerprint of excitons in momentum microscopy and highlight that it is possible to obtain information not only on the electron- but also hole-component. Second, we focus on the recent application of photoemission orbital tomography to such excitons, and discuss how this provides a unique access to the real-space properties of the exciton wavefunction. We detail how studies performed on two-dimensional transition metal dichalcogenides and organic semiconductors lead to very similar conclusions, and, in this manner, highlight the strength of momentum microscopy for the study of optical excitations in semiconductors
Towards full surface Brillouin zone mapping by coherent multi-photon photoemission
No full textOpen-Access-Publikationsfonds 202
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