Trond Andersen

Observation of Interlayer Phonon Modes in Van Der Waals Heterostructures

We have investigated the vibrational properties of van der Waals heterostructures of monolayer transition metal dichalcogenides (TMDs), specifically

Competing channels for hot-electron cooling in graphene.

\mathrm{Mo}{\mathrm{S}}_{2}/\mathrm{WS}{\mathrm{e}}_{2}

Efficiency of Launching Highly Confined Polaritons by Infrared Light Incident on a Hyperbolic Material

and

Hyperbolic phonon polaritons in hexagonal boron nitride(Conference Presentation)

\mathrm{MoS}{\mathrm{e}}_{2}/\mathrm{Mo}{\mathrm{S}}_{2}

Subdiffractional focusing and guiding of polaritonic rays in a natural hyperbolic material

heterobilayers and twisted

Tuning ultrafast electron thermalization pathways in a van der Waals heterostructure

\mathrm{Mo}{\mathrm{S}}_{2}

Towards NV-based magnetic sensing in the time domain

bilayers, by means of ultralow-frequency Raman spectroscopy. We discovered Raman features (at

Probing magnetic noise from currents and spins in 2d layered materials using diamond NV centers

30\char21{}40\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}

Using diamond NV centers to probe magnetic properties of 2d materials

) that arise from the layer-breathing mode (LBM) vibration between the two incommensurate TMD monolayers in these structures. The LBM Raman intensity correlates strongly with the suppression of photoluminescence that arises from interlayer charge transfer. The LBM is generated only in bilayer areas with direct layer-layer contact and an atomically clean interface. Its frequency also evolves systematically with the relative orientation between the two layers. Our research demonstrates that the LBM can serve as a sensitive probe to the interface environment and interlayer interactions in van der Waals materials.

Emission and propagation of hyperbolic phonon polaritons in hexagonal boron nitride

We report on temperature-dependent photocurrent measurements of high-quality dual-gated monolayer graphene p-n junction devices. A photothermoelectric effect governs the photocurrent response in our devices, allowing us to track the hot-electron temperature and probe hot-electron cooling channels over a wide temperature range (4 to 300 K). At high temperatures (T > T(*)), we found that both the peak photocurrent and the hot spot size decreased with temperature, while at low temperatures (T < T(*)), we found the opposite, namely that the peak photocurrent and the hot spot size increased with temperature. This nonmonotonic temperature dependence can be understood as resulting from the competition between two hot-electron cooling pathways: (a) (intrinsic) momentum-conserving normal collisions that dominates at low temperatures and (b) (extrinsic) disorder-assisted supercollisions that dominates at high temperatures. Gate control in our high-quality samples allows us to resolve the two processes in the same device for the first time. The peak temperature T(*) depends on carrier density and disorder concentration, thus allowing for an unprecedented way of controlling graphenes photoresponse.