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Ulrich Noumbe

Publications and source records attributed to Ulrich Noumbe.

2 recordsLinked to original sources

Exciton-induced magnons carrying orbital angular momentum in CrI3

Magnons are collective spin excitations that contain and transport spin angular momentum in magnetic materials. It has been suggested that they can also carry orbital angular momentum in analogy to the electronic motion around the nucleus. We explore the real-space topology of magnon wave-packets emanating from atomic-like excitons in the ferromagnetic insulator CrI3 and demonstrate the existence of orbital angular momentum in such wave-packets. We reveal that orbital angular momentum of magnons is nearly equal to their spin angular momentum and compensates the latter. This illustrates the existence of an unexplored internal angular momentum balance and demonstrates that the magnetization can be quenched without the need of angular momentum exchange with the lattice.

cond-mat.mtrl-sci

Direct observation of nanometer-scale orbital angular momentum accumulation

Conversion of charge to orbital angular momentum through the orbital Hall effect (OHE) holds transformative potential for the development of orbital-based electronics, however, it is challenging to directly observe the electrically generated orbital accumulation. Here, we detect the OHE by directly quantifying the orbital accumulation along the edges of a titanium thin film using a scanning transmission electron microscope. We measure the Ti L-edge using electron energy-loss spectroscopy with nanometer resolution and find a sizable orbital accumulation at the sample's outer perimeters, consistent with all signatures expected for the OHE, and determine an orbital diffusion length $\ell_o \approx 7.3$ nm. Our data points to a surprising dependence of the orbital diffusion length on the nano-structural morphology.

cond-mat.mes-hall