1,721,122 research outputs found
Orbital angular momentum structure of an unoccupied spin-split quantum-well state in Pb/Cu(111)
No full textMorphological modifications of Ag/Cu(111) probed by photoemission spectroscopy of quantum well states and the Shockley surface state
No full textDevelopment of an analytical simulation framework for angle-resolved photoemission spectra
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
Quantum-Well Wave-Function Localization and the Electron-Phonon Interaction in Thin Ag Nanofilms
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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
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