PhD positions

There are currently PhD positions available.

Topics:
  • Single embedded magnetic atoms. Strong correlations and spinorbit interactions as basis for ultimately small quantum devices
  • Atomistic theory of impurities and correlations in two dimensional materials

For further details please contact Prof. T. Wehling (wehling - at - itp.uni-bremen.de).

We analyze the interplay of spin-valley coupling, orbital physics, and magnetic anisotropy taking place at single magnetic atoms adsorbed on semiconducting transition metal dichalcogenides, MX2 (M = Mo, W; X = S, Se). Orbital selection rules turn out to govern the kinetic exchange coupling between the adatom and charge carriers in the MX2 and lead to highly orbitally dependent spin-flip scattering rates, as we illustrate for the example of transition metal adatoms with d9 configuration. Our ab initio calculations suggest that d9 configurations are realizable by single Co, Rh, or Ir adatoms on MoS2, which additionally exhibit a sizable magnetic anisotropy. We find that the interaction of the adatom with carriers in the MX2 allows to tune its behavior from a quantum regime with full Kondo screening to a regime of ”Ising spintronics” where its spin–orbital moment acts as classical bit, which can be erased and written electronically and optically.

We investigate how external screening shapes excitons in two-dimensional semiconductors embedded in laterally structured dielectric environments. An atomic scale view of these elementary excitations is developed using models which apply to a variety of materials including transition metal dichalcogenides. We find that structured dielectrics imprint a peculiar potential energy landscape on excitons in these systems: While the ground-state exciton is least influenced, higher excitations are attracted towards regions with high dielectric constant of the environment. This landscape is “inverted” in the sense that low energy excitons are less strongly affected than their higher energy counterparts. Corresponding energy variations emerge on length scales of the order of a few unit cells. This opens the prospect of trapping and guiding of higher excitons by means of tailor-made dielectric substrates on ultimately small spatial scales.