Erik van Loon

I have moved to Lund University

dr. Erik G. C. P. van Loon
E-mail evloon at itp dot uni-bremen dot de
Room NW1 O3040
Otto-Hahn-Allee 1
University of Bremen
28359, Bremen, Germany
Telephone +49 421 218 62041

Since January 2020, I hold an independent postdoc position supported by the Central Research Development Fund of the University of Bremen, working on the Theory of plasmonic and optical excitations in correlated electron materials. I have been working in the group of prof. dr. Wehling at the University of Bremen since October 2018. From December 2013 until September 2018, I was in the Theory of Condensed Matter group of prof. dr. Katsnelson, part of the Institute for Molecules and Materials of the Radboud University Nijmegen. On March 20 2018, I defended my PhD thesis Collective Phenomena in Strongly Correlated Systems. I finished my Master in the same group, having spent a year as an exchange student doing research in the group of prof. dr. Alexander Lichtenstein in Hamburg.

Research

My main interest is the study of collective excitations in strongly correlated systems.

Over the last three decades, Dynamical Mean-Field Theory (DMFT) has emerged as the best tool to describe the electronic structure of strongly correlated materials. It relies the assumption that most correlations occur locally and can be captured in a single-site reference model. This approach has been hugely successful at describing the one-particle properties of correlated models (Hubbard model) and materials: for example, the density of states, self-energy and spectral function. As a non-perturbative technique, DMFT can be used at arbitrary interaction strength and can follow the evolution from weakly interacting metal via strongly correlated metal to Mott insulator.

My work has focused on the collective properties of this kind of systems: compressibility, magnetic susceptibility, dielectric function, charge-density waves, etc. These used to be too difficult to accurately determine computationally, due to a difference in length scales. The DMFT approach knows about on-site correlations, but not about momentum dependence and long wavelengths. These aspect are necessary for determining the dispersion of collective modes (plasmons, magnons and zero-sound modes) as well as for investigating charge-density waves.

Diagrammatic extensions of DMFT address this deficiency, by adding spatial correlations to the DMFT solution. I have been working on one of these extensions, the Dual Boson approach. An important aspect in these investigations is the issue of consistency: Approximate solutions can violate known exact properties of the system. For the case of the charge susceptibility, we have shown that the Dual Boson approach gives results satisfying the charge conservation law, by taking into account vertex corrections to all orders via the so-called ladder equation. With this machinery, we were able to study the renormalization of the plasmon dispersion due to correlation. In addition to this, we have investigated charge ordering in the extended Hubbard model, with applications to dipolar fermions in optical lattices, and the competition of electron-electron and electron-phonon interaction in NbS2.

Publications

  1. 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
    [arXiv:2103.04419]
  2. Downfolding approaches to electron-ion coupling: Constrained density-functional perturbation theory for molecules
    Erik G. C. P. van Loon, Jan Berges, Tim O. Wehling
    [arXiv:2102.10072]
  3. 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
    [arXiv:2101.01140]
  4. 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
    [arXiv:2012.04562]
  5. Second-order dual fermion for multi-orbital systems
    Erik G. C. P. van Loon
    J. Phys.: Condens. Matter 33 135601 (2021)[arXiv:2011.08780]
  6. The Bethe-Salpeter equation at the critical end-point of the Mott transition
    Erik G. C. P. van Loon, Friedrich Krien and Andrey Katanin
    Phys. Rev. Lett. 125, 136402 (2020)[arXiv:2002.12745]
  7. 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
    [arXiv:2001.01735]
  8. 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
    Nature Communications 11, 3997 (2020)[arXiv:1911.06810]
  9. 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
    Phys. Rev. B 101, 155107 (2020)[arXiv:1911.02450]
  10. 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
    ACS Nano 13, 10210 (2019)
  11. 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
    SciPost Phys. 6, 067 (2019)[arXiv:1903.09947]
  12. 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
    Phys. Rev. B 100, 165128 (2019)[arXiv:1902.06604]
  13. 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
    J. Phys.: Condens. Matter 31, 465603 (2019)[arXiv:1901.11257]
  14. 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
    Phys. Rev. B 99, 245128 (2019)[arXiv:1811.00362]
  15. 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
    Phys. Rev. B 98, 205148 (2018)[arXiv:1806.10415]
  16. 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
    Phys. Rev. B 98, 155117 (2018)[arXiv:1805.08572]
  17. Confining graphene plasmons to the ultimate limit
    Alessandro Principi, Erik van Loon, Marco Polini and Mikhail I. Katsnelson
    Phys. Rev. B 98, 035427 (2018)[arXiv:1802.06797]
  18. 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
    Phys. Rev. B 97, 165135 (2018)[arXiv:1706.09644]
  19. Precursors of the insulating state in the square-lattice Hubbard model
    E. G. C. P. van Loon, Hartmut Hafermann and M. I. Katsnelson
    Phys. Rev. B 97, 085125 (2018)[arXiv:1712.08379]
  20. The extended Hubbard model with attractive interactions
    E. G. C. P. van Loon and M. I. Katsnelson
    J. Phys.: Conf. Ser., 1136, 012006 (2018)[arXiv:1709.06379]
  21. Competing Coulomb and electron–phonon interactions in NbS2
    E. G. C. P. van Loon, M. Rösner, G. Schönhoff, M. I. Katsnelson, T. O. Wehling
    npj Quantum Materials 3, 32 (2018)[arXiv:1707.05640]
  22. 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
    Phys. Rev. B 96, 075155 (2017)[arXiv:1706.10233]
  23. 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
    Phys. Rev. B 94, 245140 (2016)[arXiv:1607.04212]
  24. 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
    Phys. Rev. B 94, 205110 (2016)[arXiv:1604.07734]
  25. 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
    Phys. Rev. B 94, 165141 (2016)[arXiv:1605.09140]
  26. Interaction-driven Lifshitz transition with dipolar fermions in optical lattices
    E. G. C. P. van Loon, M. I. Katsnelson, L. Chomaz, M. Lemeshko
    Phys. Rev. B 93, 195145 (2016)[arXiv:1603.09358]
  27. 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
    Phys. Rev. B 93, 155162 (2016)[arXiv:1602.09129]
  28. 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
    Phys. Rev. B 93, 045107 (2016)[arXiv:1508.07237]
  29. Ultralong-range order in the Fermi-Hubbard model with long-range interactions
    Erik G. C. P. van Loon, Mikhail I. Katsnelson and Mikhail Lemeshko
    Phys. Rev. B 92, 081106(R) (2015)[arXiv:1506.06007]
  30. 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
    Phys. Rev. B 92, 085106 (2015)[arXiv:1505.05305]
  31. 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
    Phys. Rev. B 90, 235135 (2014)[arXiv:1408.2150]
  32. 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
    Phys. Rev. Lett. 113, 246407 (2014)[arXiv:1406.6188]
  33. 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
    Phys. Rev. B 90, 235105 (2014)[arXiv:1406.6515]

Popular Publications

  1. Faseovergangen door quantumonzekerheid
    Jins de Jong, Lennert van Tilburg en Erik van Loon
    Nederland Tijdschrift voor Natuurkunde, november 2012