Publications (61)
Dark exciton-exciton annihilation in monolayer WSe
Daniel Erkensten, Samuel Brem, Koloman Wagner +8
The exceptionally strong Coulomb interaction in semiconducting transition-metal dichalcogenides (TMDs) gives rise to a rich exciton landscape consisting of bright and dark exciton…
Ultrafast dynamics of bright and dark excitons in monolayer WSe and heterobilayer WSe/MoS
Jan Philipp Bange, Paul Werner, David Schmitt +15
The energy landscape of optical excitations in mono- and few-layer transition metal dichalcogenides (TMDs) is dominated by optically bright and dark excitons. These excitons can be…
Non-equilibrium diffusion of dark excitons in atomically thin semiconductors
Roberto Rosati, Koloman Wagner, Samuel Brem +7
Atomically thin semiconductors provide an excellent platform to study intriguing many-particle physics of tightly-bound excitons. In particular, the properties of tungsten-based tr…
Brightening of spin- and momentum-dark excitons in transition metal dichalcogenides
Maja Feierabend, Samuel Brem, August Ekman +1
Monolayer transition metal dichalcogenides (TMDs) have been in focus of current research, among others due to their remarkable exciton landscape consisting of bright and dark excit…
The moiré potential in twisted transition metal dichalcogenide bilayers
Christopher Linderälv, Joakim Hagel, Samuel Brem +2
Moiré superlattices serve as a playground for emerging phenomena, such as localization of band states, superconductivity, and localization of excitons. These superlattices are lar…
Carrier dynamics in graphene: ultrafast many-particle phenomena
Ermin Malic, Torben Winzer, Florian Wendler +10
Graphene is an ideal material to study fundamental Coulomb- and phonon-induced carrier scattering processes. Its remarkable gapless and linear band structure opens up new carrier r…
Polaron-induced changes in moiré exciton propagation in twisted van der Waals heterostructures
Willy Knorr, Samuel Brem, Giuseppe Meneghini +1
Twisted transition metal dichalcogenides (TMDs) present an intriguing platform for exploring excitons and their transport properties. By introducing a twist angle, a moiré superla…
Exciton Relaxation Cascade in Two-dimensional Transition-metal dichalcogenides
Samuel Brem, Gunnar Berghaeuser, Malte Selig +1
Monolayers of transition-metal dichalcogenides (TMDs) are characterized by an extraordinarily strong Coulomb interaction giving rise to tightly bound excitons with binding energies…
Molecule signatures in photoluminescence spectra of transition metal dichalcogenides
Maja Feierabend, Gunnar Berghaeuser, Malte Selig +4
Monolayer transition metal dichalcogenides (TMDs) show an optimal surface-to-volume ratio and are thus promising candidates for novel molecule sensor devices. It was recently predi…
Trion-phonon interaction in atomically thin semiconductors
Raul Perea-Causin, Samuel Brem, Ermin Malic
Optical and transport properties of doped monolayer semiconductors are dominated by trions, which are three-particle compounds formed by two electrons and one hole or vice versa. I…
Intrinsic Lifetime of Higher Excitonic States in Tungsten Diselenide Monolayers
Samuel Brem, Jonas Zipfel, Malte Selig +7
The reduced dielectric screening in atomically thin transition metal dichalcogenides allows to study the hydrogen-like series of higher exciton states in optical spectra even at ro…
Quadrupolar Excitons in MoSe Bilayers
Jakub JasiÅski, Joakim Hagel, Samuel Brem +11
The quest for platforms to generate and control exotic excitonic states has greatly benefited from the advent of transition metal dichalcogenide (TMD) monolayers and their heterost…
Twist Angle Dependence of Exciton Resonances in WSe/MoSe Moiré Heterostructures
Chirag Chandrakant Palekar, Joakim Hagel, Barbara Rosa +7
Van der Waals heterostructures based on TMDC semiconducting materials have emerged as promising materials due to their spin-valley properties efficiently contrived by the stacking-…
Spatiotemporal dynamics of moiré excitons in van der Waals heterostructures
Giuseppe Meneghini, Samuel Brem, Ermin Malic
Heterostructures of transition metal dichalcogenides (TMDs) offer unique opportunities in optoelectronics due to their strong light-matter interaction and the formation of dipolar…
Electrical tuning of moiré excitons in MoSe bilayers
Joakim Hagel, Samuel Brem, Ermin Malic
Recent advances in the field of vertically stacked 2D materials have revealed a rich exciton landscape. In particular, it has been demonstrated that out-of-plane electrical fields…
Interlayer exciton dynamics in van der Waals heterostructures
Simon Ovesen, Samuel Brem, Christopher Linderälv +4
Exciton binding energies of hundreds of meV and strong light absorption in the optical frequency range make transition metal dichalcogenides (TMDs) promising for novel optoelectron…
Ultrafast nano-imaging of dark excitons
David Schmitt, Jan Philipp Bange, Wiebke Bennecke +15
The role and impact of spatial heterogeneity in two-dimensional quantum materials represents one of the major research quests regarding the future application of these materials in…
Hybridized intervalley moiré excitons and flat bands in twisted WSe bilayers
Samuel Brem, Kai-Qiang Lin, Roland Gillen +4
The large surface-to-volume ratio in atomically thin 2D materials allows to efficiently tune their properties through modifications of their environment. Artificial stacking of two…
Nonclassical Exciton Diffusion in Monolayer WSe2
Koloman Wagner, Jonas Zipfel, Roberto Rosati +9
We experimentally demonstrate time-resolved exciton propagation in a monolayer semiconductor at cryogenic temperatures. Monitoring phonon-assisted recombination of dark states, we…
Trion photoluminescence and trion stability in atomically thin semiconductors
Raul Perea-Causin, Samuel Brem, Ole Schmidt +1
The optical response of doped monolayer semiconductors is governed by trions, i.e. photoexcited electron-hole pairs bound to doping charges. While their photoluminescence (PL) sign…
Exciton diffusion in monolayer semiconductors with suppressed disorder
Jonas Zipfel, Marvin Kulig, Raül Perea-CausÃn +8
Tightly bound excitons in monolayer semiconductors represent a versatile platform to study two-dimensional propagation of neutral quasiparticles. Their intrinsic properties, howeve…
Impact of atomic reconstruction on optical spectra of twisted TMD homobilayers
Joakim Hagel, Samuel Brem, Johannes Abelardo Pineiro +1
Twisted bilayers of transition metal dichalcogenides (TMDs) have revealed a rich exciton landscape including hybrid excitons and spatially trapped moiré excitons that dominate the…
Strain-dependent exciton diffusion in transition metal dichalcogenides
Roberto Rosati, Samuel Brem, Raül Perea-CausÃn +5
Monolayers of transition metal dichalcogenides (TMDs) have a remarkable excitonic landscape with deeply bound bright and dark exciton states. Their properties are strongly affected…
Symmetry-breaking supercollisions in Landau-quantized graphene
Florian Wendler, Martin Mittendorff, Jacob C. König-Otto +8
Recent pump-probe experiments performed on graphene in a perpendicular magnetic field have revealed carrier relaxation times ranging from picoseconds to nanoseconds depending on th…
Proposal for a tunable graphene-based terahertz Landau-level laser
Samuel Brem, Florian Wendler, Ermin Malic
In the presence of strong magnetic fields the electronic bandstructure of graphene drastically changes. The Dirac cone collapses into discrete non-equidistant Landau levels, which…
Negative excitonic diffusion in transition metal dichalcogenides
Roberto Rosati, Raül Perea-CausÃn, Samuel Brem +1
While exciton relaxation in transition metal dichalcogenides (TMDs) has been intensively studied, spatial exciton propagation has received only little attention - in spite of being…
Optical fingerprint of bright and dark localized excitonic states in atomically thin 2D materials
Maja Feierabend, Samuel Brem, Ermin Malic
Point defects, local strain or impurities can crucially impact the optical response of atomically thin two-dimensional materials as they offer trapping potentials for excitons. The…
Ultrafast phonon-driven charge transfer in van der Waals heterostructures
Giuseppe Meneghini, Samuel Brem, Ermin Malic
Van der Waals heterostructures built by vertically stacked transition metal dichalcogenides (TMDs) exhibit a rich energy landscape including interlayer and intervalley excitons. Re…
Electrically tunable layer-hybridized trions in doped WSe bilayers
Raul Perea-Causin, Samuel Brem, Fabian Buchner +6
Doped van der Waals heterostructures host layer-hybridized trions, i.e. charged excitons with layer-delocalized constituents holding promise for highly controllable optoelectronics…
Stability of Wigner crystals and Mott insulators in twisted moiré structures
Daniel Erkensten, Samuel Brem, Raul Perea-Causin +1
Transition metal dichalcogenides (TMDs) constitute an intriguing platform for studying charge-ordered states including conventional and generalized Wigner crystals as well as Mott…
Momentum-resolved observation of exciton formation dynamics in monolayer WS
Robert Wallauer, Raul Perea-Causin, Lasse Münster +8
The dynamics of exciton formation in transition metal dichalcogenides is difficult to measure experimentally, since many momentum-indirect exciton states are not accessible to opti…
Exciton propagation and halo formation in two-dimensional materials
Raul Perea-Causin, Samuel Brem, Roberto Rosati +6
The interplay of optics, dynamics and transport is crucial for the design of novel optoelectronic devices, such as photodetectors and solar cells. In this context, transition metal…
Dielectric Engineering of Electronic Correlations in a van der Waals Heterostructure
Philipp Steinleitner, Philipp Merkl, Alexander Graf +10
Heterostructures of van der Waals bonded layered materials offer unique means to tailor dielectric screening with atomic-layer precision, opening a fertile field of fundamental res…
Exciton landscape in van der Waals heterostructures
Joakim Hagel, Samuel Brem, Christopher Linderälv +2
van der Waals heterostructures consisting of vertically stacked transition-metal dichalcogenides (TMDs) exhibit a rich landscape of bright and dark intra- and interlayer excitons.…
Exciton transport in a moiré potential: from hopping to dispersive regime
Willy Knorr, Samuel Brem, Giuseppe Meneghini +1
The propagation of excitons in TMD monolayers has been intensively studied revealing interesting many-particle effects, such as halo formation and non-classical diffusion. Initial…
Terahertz fingerprint of monolayer Wigner crystals
Samuel Brem, Ermin Malic
The strong Coulomb interaction in monolayer semiconductors represents a unique opportunity for the realization of Wigner crystals without external magnetic fields. In this work, we…
Criteria for deterministic single-photon emission in two-dimensional atomic crystals
Joshua J. P. Thompson, Samuel Brem, Hanlin Fang +4
The deterministic production of single-photons from two dimensional materials promises to usher in a new generation of photonic quantum devices. In this work, we outline criteria b…
Polarization and charge-separation of moiré excitons in van der Waals heterostructures
Joakim Hagel, Samuel Brem, Ermin Malic
Twisted transition metal dichalcogenide (TMD) bilayers exhibit periodic moiré potentials, which can trap excitons at certain high-symmetry sites. At small twist angles, TMD lattic…
Ultrafast transition between exciton phases in van der Waals heterostructures
Philipp Merkl, Fabian Mooshammer, Philipp Steinleitner +11
Heterostructures of atomically thin van der Waals bonded monolayers have opened a unique platform to engineer Coulomb correlations, shaping excitonic, Mott insulating, or supercond…
Electrically tunable dipolar interactions between layer-hybridized excitons
Daniel Erkensten, Samuel Brem, Raul Perea-Causin +5
Transition-metal dichalcogenide bilayers exhibit a rich exciton landscape including layer-hybridized excitons, i.e. excitons which are of partly intra- and interlayer nature. In th…
Phonon-assisted Exciton Dissociation in Transition Metal Dichalcogenides
Raul Perea-Causin, Samuel Brem, Ermin Malic
Monolayers of transition metal dichalcogenides (TMDs) have been established in the last years as promising materials for novel optoelectronic devices. However, the performance of s…
Temporal evolution of low-temperature phonon sidebands in WSe monolayers
Roberto Rosati, Samuel Brem, Raül Perea-CausÃn +9
Low-temperature photoluminescence (PL) of hBN-encapsulated monolayer tungsten diselenide (WSe) shows a multitude of sharp emission peaks below the bright exciton. Some of them…
Bosonic Delocalization of Dipolar Moiré Excitons
Samuel Brem, Ermin Malic
In superlattices of twisted semiconductor monolayers, tunable moiré potentials emerge, trapping excitons into periodic arrays. In particular, spatially separated interlayer excito…
Impact of strain on the excitonic linewidth in transition metal dichalcogenides
Zahra Khatibi, Maja Feierabend, Malte Selig +4
Monolayer transition metal dichalcogenides (TMDs) are known to be highly sensitive to externally applied tensile or compressive strain. In particular, strain can be exploited as a…
Microscopic origin of anomalous interlayer exciton transport in van der Waals heterostructures
Daniel Erkensten, Samuel Brem, Raül Perea-Causin +1
Van der Waals heterostructures constitute a platform for investigating intriguing many-body quantum phenomena. In particular, transition-metal dichalcogenide (TMD) hetero-bilayers…
Phonon-assisted Photoluminescence from Dark Excitons in Monolayers of Transition Metal Dichalcogenides
Samuel Brem, August Ekman, Dominik Christiansen +7
The photoluminescence (PL) spectrum of transition metal dichalcogenides (TMDs) shows a multitude of emission peaks below the bright exciton line and not all of them have been expla…
Excitonic thermalization bottleneck in twisted TMD heterostructures
Giuseppe Meneghini, Samuel Brem, Ermin Malic
Twisted van der Waals heterostructures show an intriguing interface exciton physics including hybridization effects and emergence of moiré potentials. Recent experiments have reve…
Valley-exchange coupling probed by angle-resolved photoluminescence
Joshua J. P Thompson, Samuel Brem, Hanlin Fang +7
The optical properties of monolayer transition metal dichalcogenides are dominated by tightly-bound excitons. They form at distinct valleys in reciprocal space, and can interact vi…
Direct visualization of hybrid excitons in van der Waals heterostructures
Giuseppe Meneghini, Marcel Reutzel, Stefan Mathias +2
Van der Waals heterostructures show fascinating physics including trapped moire exciton states, anomalous moire exciton transport, generalized Wigner crystals, etc. Bilayers of tra…
Link between interlayer hybridization and ultrafast charge transfer in WS-graphene heterostructures
Niklas Hofmann, Leonard Weigl, Johannes Gradl +12
Ultrafast charge separation after photoexcitation is a common phenomenon in various van-der-Waals (vdW) heterostructures with great relevance for future applications in light harve…
Exciton-exciton interaction in transition metal dichalcogenide monolayers and van der Waals heterostructures
Daniel Erkensten, Samuel Brem, Ermin Malic
Due to a strong Coulomb interaction, excitons dominate the excitation kinetics in 2D materials. While Coulomb-scattering between electrons has been well studied, the interaction of…
Probing correlations in the exciton landscape of a moiré heterostructure
Jan Philipp Bange, David Schmitt, Wiebke Bennecke +13
Excitons are two-particle correlated bound states that are formed due to Coulomb interaction between single-particle holes and electrons. In the solid-state, cooperative interactio…
Exciton optics, dynamics and transport in atomically thin semiconductors
Raul Perea-Causin, Daniel Erkensten, Jamie M. Fitzgerald +4
Atomically thin semiconductors such as transition metal dichalcogenide (TMD) monolayers exhibit a very strong Coulomb interaction, giving rise to a rich exciton landscape. This mak…
Electrically tunable ultrafast dynamics and interactions of hybrid excitons in a 2D semiconductor bilayer
Edoardo Lopriore, Charalambos Louca, Armando Genco +12
Extended efforts have been devoted to the study of strongly-interacting excitons and their dynamics, towards macroscopic quantum states of matter such as Bose-Einstein condensates…
Dark excitons in transition metal dichalcogenides
Ermin Malic, Malte Selig, Maja Feierabend +5
Monolayer transition metal dichalcogenides (TMDs) exhibit a remarkably strong Coulomb interaction that manifests in tightly bound excitons. Due to the complex electronic band struc…
Optical Signatures of Moiré Trapped Biexcitons
Samuel Brem, Ermin Malic
Atomically thin heterostructures formed by twisted transition metal dichalcogenides can be used to create periodic moiré patterns. The emerging moiré potential can trap interlaye…
Tunable Phases of Moiré Excitons in van der Waals Heterostructures
Samuel Brem, Christopher Linderälv, Paul Erhart +1
Stacking monolayers of transition metal dichalcogenides into a heterostructure with a finite twist-angle gives rise to artificial moiré superlattices with a tunable periodicity. A…
A room-temperature moiré interlayer exciton laser
Qiaoling Lin, Hanlin Fang, Yuanda Liu +10
Moiré superlattices in van der Waals heterostructures offer highly tunable quantum systems with emergent electronic and excitonic properties such as superconductivity, topological…
Electrical control of hybrid exciton transport in a van der Waals heterostructure
Fedele Tagarelli, Edoardo Lopriore, Daniel Erkensten +9
Interactions between out-of-plane dipoles in bosonic gases enable the long-range propagation of excitons. The lack of direct control over collective dipolar properties has hitherto…
Quenching of Intervalley Exchange Coupling in the Presence of Momentum-Dark States in TMDCs
Malte Selig, Florian Katsch, Samuel Brem +3
Monolayers of transition metal dichalcogenides are promising materials for valleytronic applications, since they possess two individually addressable excitonic transitions at the n…
Spatio-temporal dynamics in graphene
Roland Jago, Raül Perea-Causin, Samuel Brem +1
Temporally and spectrally resolved dynamics of optically excited carriers in graphene has been intensively studied theoretically and experimentally, whereas carrier diffusion in sp…