Erik van Loon

Contact details

E-mailerik.van_loon AT

Division of Mathematical Physics
Department of Physics
Lund University
Box 118
SE - 221 00 Lund

About me

I have been working as an Associate Senior University Lecturer at Lund University since March 2021. My main research interest is the study of strongly correlated electrons and their collective excitations. I am also involved in teaching at the bachelor and master/PhD level. More information about my teaching, research and publications can be found below.

Previously, I was working with Professor Wehling at the University of Bremen (2018-2021). I did my PhD with Professor Katsnelson at Radboud University (2013-2018). Radboud University is also where I studied Physics, with a research stay with Professor Alexander Lichtenstein in Hamburg for my MSc. thesis.

MSc. and BSc. Thesis projects

Thesis projects on topics in condensed matter theory are available, with a focus on the quantum mechanics of correlated systems. Most projects will involve a combination of theoretical and computational studies. For MSc. thesis project, prior knowledge of advanced quantum mechanics and solid state physics are beneficial. If you are interested in doing a thesis project with me, please contact me via e-mail (see above) so that we can find a suitable project for you.


I am currently responsible for the courses FYSB23 and FYST25. More information about the courses can be found on their respective Canvas pages. Please contact me by e-mail if you encounter problems in the registration process or if you have questions about the course.

Basic Statistical Physics and Quantum Statistics (FYSB 23, next given Spring 2022)

Solid State Theory (FYST25/EXTP90/NAFY017, next given Spring 2022)


My main interest is the study of collective, many-particle excitations in strongly correlated electron systems. The Coulomb interaction between electrons leads to both spatial and temporal correlations between these particles. In strongly correlated systems, this effect is so strong that a description based on independent (quasi-)particles breaks down completely and alternative theoretical frameworks need to be found. Indeed, over the last three decades, it has emerged that temporal and spatial correlations can largely be separated and that the former can be captured in a mean-field fashion, the so-called Dynamical Mean-Field Theory. In this way, the correlation-driven Mott metal-insulator is found: sufficiently strong electronic repulsion can immobilize the electrons and make a system insulating, even when it should be a metal according to band theory.

My work has focused on the collective properties of this kind of systems: compressibility, magnetic susceptibility, dielectric function, charge-density waves, etc. Some of these can be studied within DMFT, but it turns out that spatial correlations are more important for these collective properties than they are for single-particle properties. Diagrammatic extensions of DMFT address this deficiency, by adding spatial correlations back onto the DMFT solution. An important aspect in these investigations is the issue of consistency: Approximate solutions can violate known exact properties of the system. We have shown that appropriate diagrammatic expansions recover several of the exact properties, including charge conservation and thermodynamic consistency of response functions.

Several diagrammatic extensions of DMFT exist, my work has focussed on two of them which are called the dual fermion and dual boson approach. During my PhD, I implemented the dual boson approach for single-orbital systems and used it to study plasmons and charge-density waves, among other things. I currently maintain an open source code for multi-orbital dual fermion calculations, which can be found here:


  1. Two-particle correlations and the metal-insulator transition: Iterated Perturbation Theory revisited
    Erik G. C. P. van Loon
  2. Local Plaquette Physics as Key Ingredient of High-Temperature Superconductivity in Cuprates
    M. Danilov, E.G.C.P. van Loon, S. Brener, S. Iskakov, M.I. Katsnelson, A.I. Lichtenstein
  3. Downfolding the Su-Schrieffer-Heeger model
    Arne Schobert, Jan Berges, Tim Wehling and Erik van Loon
    SciPost Phys. 11, 079 (2021) [arXiv:2104.09207]
  4. Random Phase Approximation for gapped systems: role of vertex corrections and applicability of the constrained random phase approximation
    Erik G. C. P. van Loon, Malte Rösner, Mikhail I. Katsnelson, Tim O. Wehling
    Phys. Rev. B 104, 045134 (2021)  [arXiv:2103.04419]
  5. Downfolding approaches to electron-ion coupling: Constrained density-functional perturbation theory for molecules
    Erik G. C. P. van Loon, Jan Berges, Tim O. Wehling
  6. A full gap above the Fermi level: the charge density wave of monolayer VS2
    Camiel van Efferen, Jan Berges, Joshua Hall, Erik van Loon, Stefan Kraus, Arne Schobert, Tobias Wekking, Felix Huttmann, Eline Plaar, Nico Rothenbach, Katharina Ollefs, Lucas Machado Arruda, Nick Brookes, Gunnar Schoenhoff, Kurt Kummer, Heiko Wende, Tim Wehling, Thomas Michely
  7. An efficient fluctuation exchange approach to low-temperature spin fluctuations and superconductivity: from the Hubbard model to NaxCoO2⋅yH2O
    Niklas Witt, Erik G. C. P. van Loon, Takuya Nomoto, Ryotaro Arita, Tim Wehling
  8. Second-order dual fermion for multi-orbital systems
    Erik G. C. P. van Loon
  9. The Bethe-Salpeter equation at the critical end-point of the Mott transition
    Erik G. C. P. van Loon, Friedrich Krien and Andrey Katanin
  10. Coulomb Engineering of two-dimensional Mott materials
    Erik G. C. P. van Loon, Malte Schüler, Daniel Springer, Giorgio Sangiovanni, Jan M. Tomczak, Tim O. Wehling
  11. Turbulent hydrodynamics in strongly correlated Kagome metals
    Domenico Di Sante, Johanna Erdmenger, Martin Greiter, Ioannis Matthaiakakis, Rene Meyer, David Rodriguez Fernandez, Ronny Thomale, Erik van Loon, Tim Wehling
  12. Ab-initio phonon self-energies and fluctuation diagnostics of phonon anomalies: lattice instabilities from Dirac pseudospin physics in transition-metal dichalcogenides
    Jan Berges, Erik G. C. P. van Loon, Arne Schobert, Malte Rösner, Tim O. Wehling
  13. Environmental control of charge density wave order in monolayer 2H-TaS2
    Joshua Hall, Niels Ehlen, Jan Berges, Erik van Loon, Camiel van Efferen, Clifford Murray, Malte Rösner, Jun Li, Boris V. Senkovskiy, Martin Hell, Matthias Rolf, Tristan Heider, María C. Asensio, José Avila, Lukasz Plucinski, Tim Wehling, Alexander Grüneis and Thomas Michely
  14. Thermodynamics of the metal-insulator transition in the extended Hubbard model
    M. Schüler, E. G. C. P. van Loon, M. I. Katsnelson, T. O. Wehling
  15. Dual Boson approach with instantaneous interaction
    L. Peters, E. G. C. P. van Loon, A. N. Rubtsov, A. I. Lichtenstein, M. I. Katsnelson, E. A. Stepanov
  16. Bandwidth renormalization due to the intersite Coulomb interaction
    Yann in ‘t Veld, Malte Schüler, Tim Wehling, Mikhail I. Katsnelson, Erik G. C. P. van Loon
  17. Two-particle Fermi liquid parameters at the Mott transition: Vertex divergences, Landau parameters, and incoherent response in dynamical mean-field theory
    Friedrich Krien, Erik G. C. P. van Loon, Mikhail I. Katsnelson, Alexander I. Lichtenstein, Massimo Capone
  18. Fermion-boson vertex within Dynamical Mean-Field Theory
    Erik G. C. P. van Loon, Friedrich Krien, Hartmut Hafermann, Alexander I. Lichtenstein and Mikhail I. Katsnelson
  19. Second-order dual fermion approach to the Mott transition in the two-dimensional Hubbard model
    Erik G. C. P. van Loon, Mikhail I. Katsnelson and Hartmut Hafermann
  20. Confining graphene plasmons to the ultimate limit
    Alessandro Principi, Erik van Loon, Marco Polini and Mikhail I. Katsnelson
  21. First-order metal-insulator transitions in the extended Hubbard model due to self-consistent screening of the effective interaction
    M. Schüler, E. G. C. P. van Loon, M. I. Katsnelson, T. O. Wehling
  22. Precursors of the insulating state in the square-lattice Hubbard model
    E. G. C. P. van Loon, Hartmut Hafermann and M. I. Katsnelson
  23. The extended Hubbard model with attractive interactions
    E. G. C. P. van Loon and M. I. Katsnelson
  24. Competing Coulomb and electron–phonon interactions in NbS2
    E. G. C. P. van Loon, M. Rösner, G. Schönhoff, M. I. Katsnelson, T. O. Wehling
  25. Conservation in two-particle self-consistent extensions of dynamical-mean-field-theory
    F. Krien, E. G. C. P. van Loon, H. Hafermann, J. Otsuki, M. I. Katsnelson, A. I. Lichtenstein
  26. A comparison between methods of analytical continuation for bosonic functions
    Johan Schött, Erik G. C. P. van Loon, Inka L. M. Locht, Mikhail Katsnelson, Igor Di Marco
  27. From local to nonlocal correlations: The Dual Boson perspective
    E. A. Stepanov, A. Huber, E. G. C. P. van Loon, A. I. Lichtenstein, M. I. Katsnelson
  28. Capturing non-local interaction effects in the Hubbard model: optimal mappings and limits of applicability
    E. G. C. P. van Loon, M. Schüler, M. I. Katsnelson, T. O. Wehling
  29. Interaction-driven Lifshitz transition with dipolar fermions in optical lattices
    E. G. C. P. van Loon, M. I. Katsnelson, L. Chomaz, M. Lemeshko
  30. Double occupancy in dynamical mean-field theory and the Dual Boson approach
    Erik G. C. P. van Loon, Friedrich Krien, Hartmut Hafermann, Evgeny A. Stepanov, Alexander I. Lichtenstein, Mikhail I. Katsnelson
  31. Self-consistent Dual Boson approach to single-particle and collective excitations in correlated systems
    E. A. Stepanov, E. G. C. P. van Loon, A. A. Katanin, A. I. Lichtenstein, M. I. Katsnelson, A. N. Rubtsov
  32. Ultralong-range order in the Fermi-Hubbard model with long-range interactions
    Erik G. C. P. van Loon, Mikhail I. Katsnelson and Mikhail Lemeshko
  33. Thermodynamic consistency of the charge response in dynamical mean-field based approaches
    Erik G. C. P. van Loon, Hartmut Hafermann, Alexander I. Lichtenstein, and Mikhail I. Katsnelson
  34. Beyond extended dynamical mean-field theory: Dual boson approach to the two-dimensional extended Hubbard model
    Erik G. C. P. van Loon, Alexander I. Lichtenstein, Mikhail I. Katsnelson, Olivier Parcollet, and Hartmut Hafermann
  35. Plasmons in Strongly Correlated Systems: Spectral Weight Transfer and Renormalized Dispersion
    E. G. C. P. van Loon, H. Hafermann, A. I. Lichtenstein, A. N. Rubtsov, and M. I. Katsnelson
  36. Collective charge excitations of strongly correlated electrons, vertex corrections, and gauge invariance
    Hartmut Hafermann, Erik G. C. P. van Loon, Mikhail I. Katsnelson, Alexander I. Lichtenstein, and Olivier Parcollet

Popular Publications

  1. Faseovergangen door quantumonzekerheid
    Jins de Jong, Lennert van Tilburg en Erik van Loon
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