Theory of Quantum Systems at Surfaces


The theory team at QNS has two goals:

  1. to be just one door away for every experimentalist and aid in the explanation of new discoveries and
  2. to, in turn, guide experimentalists in our search for novel quantum spin systems on surfaces and interfaces with the goal of achieving full quantum control.

Most of our work to date is based on ab initio modelling within the framework of density functional theory (DFT). This method is suitable for treating large surface systems and small molecules at equal footing, but has some drawbacks when describing magnetic phenomena at the nanoscale due to approximations made in the implementation of DFT.
Spin-polarization isosurfaces

Spin-polarization isosurfaces of antiferromagnetically coupled nickelocene molecules, a promising candidate as "spin-filter" in STM measurements.

To overcome these limitations, QNS and collaborators have developed tools that go beyond the DFT mean field description and recover the true many-body character of the wavefunction. This allows us to accurately explore the landscape of magnetic energies and, in the near future, also the coherence times of such systems.
Low-energy spectrum of the multiplet solution of Fe on MgO

Low-energy spectrum of the multiplet solution of Fe on MgO under the influence of crystal field, spin-orbit coupling (SO) and magnetic field perpendicular to the sample (Bz)

Most of our work can be performed in-house on our mid-size high-performance computer cluster.

To expand our network, we have recently (May 2019) hosted a workshop that brought together more than 20 experts in the field of theoretical advances of spins at the nanoscale and through our visitor program we have hosted experts from all over the world, making QNS a global hub for theoretical studies of quantum phenomena on surfaces.

Long-Term Goals

  • Find surface quantum systems that are promising for the realization of full quantum control using only ab initio-based methods
  • Develop theoretical understanding of quantum coherence, with emphasis on mitigating decoherence
  • Investigate the transition from quantum to classical behavior, including the quantum measurement problem

Near-Term Goals

  • Expanding our studies from d-electron system to the more complex f-electron systems of the lanthanide series
  • Explore more systems for long magnetic lifetime and coherence times
  • Thereby guiding experimentalists in their search for such systems
  • Expand the QNS global hub with long-term and short-term visitors

Key Publications

Christoph Wolf, Fernando Delgado et al., J. Phys. Chem. A (2020) ...
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J. Reina Gálvez, C. Wolf et al., Phys. Rev. B, 2019 ...
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Himchan Cho, Joo Sung Kim et al., ACS Nano 2018 ...
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  • Christoph Wolf