# Erik van Loon

### Contact details

erik.van_loon AT teorfys.lu.se | |

Office | B310 |

Post | Division of Mathematical Physics |

### 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. This line of research is supported by the Crafoord Foundation, the Krapperup foundation and the Swedish Research Council (Vetenskapsrådet). 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.

## Teaching

I am currently responsible for the courses FYSB23 and FYST68 (formerly 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, VT1)

Solid State Theory (FYST68/EXTP90/NAFY017, VT2)

## Research

My main interest is the study of collective, many-particle excitations in strongly correlated electron systems. The Coulomb interaction between electrons means that these particles do not move independently. In fact, the electronic motion contains both spatial and temporal correlations. Dealing with this involves advanced quantum many-bod techniques, including the so-called Dynamical Mean-Field Theory (DMFT). An illustrative example of the role of correlations is the metal-insulator transition: sufficiently strong electronic repulsion can create a traffic jam of electrons, immobilizing them completely, making the electrical conductivity zero.

My work has focused on the collective properties of these systems: compressibility, magnetic susceptibility, dielectric function, charge-density waves, etc. It turns out that spatial correlations are important for these collective properties. I have been working on methods called diagrammatic extensions of DMFT to address this deficiency. 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: github.com/egcpvanloon/dualfermion

In the spring of 2022, we had an online workshop on two-particle correlations, more information can be found on the dedicated web page.

## Publications

**Unconventional charge-density-wave gap in monolayer NbS2**

Timo Knispel, Jan Berges, Arne Schobert, Erik G. C. P. van Loon, Wouter Jolie, Tim Wehling, Thomas Michely, Jeison Fischer

[arXiv:2307.13791]**Dual Bethe-Salpeter equation for the multi-orbital lattice susceptibility within dynamical mean-field theory**

Erik G. C. P. van Loon, Hugo U. R. Strand

[arXiv:2306.05157]**Nb3Cl8: A Prototypical Layered Mott-Hubbard Insulator**

Sergii Grytsiuk, Mikhail I. Katsnelson, Erik G.C.P. van Loon, Malte Rösner

[arXiv:2305.04854]**Ab initio electron-lattice downfolding: potential energy landscapes, anharmonicity, and molecular dynamics in charge density wave materials**

Arne Schobert, Jan Berges, Erik G. C. P. van Loon, Michael A. Sentef, Sergey Brener, Mariana Rossi, Tim O. Wehling

[arXiv:2303.07261]**Larmor precession in strongly correlated itinerant electron systems**

Erik G. C. P. van Loon and Hugo U. R. Strand

[arXiv:2303.03468]**Two-particle correlations and the metal-insulator transition: Iterated Perturbation Theory revisited**

Erik G. C. P. van Loon

Phys. Rev. B**105**, 245104 (2022) [arXiv:2110.11116]**Degenerate 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

npj Quantum Materials**7**, 50 (2022) [arXiv:2107.11344]**Downfolding the Su-Schrieffer-Heeger model**

Arne Schobert, Jan Berges, Tim Wehling and Erik van Loon

SciPost Phys. 11, 079 (2021) [arXiv:2104.09207]**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]**Downfolding approaches to electron-ion coupling: Constrained density-functional perturbation theory for molecules**

Erik G. C. P. van Loon, Jan Berges, Tim O. Wehling

Phys. Rev. B 103, 205103 (2021) [arXiv:2102.10072]**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

Nature Comms 12*,*6837 (2021) [arXiv:2101.01140]**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

Phys. Rev. B 103, 205148 (2021) [arXiv:2012.04562]**Second-order dual fermion for multi-orbital systems**

Erik G. C. P. van Loon

J. Phys.: Condens. Matter**33**135601 (2021)[arXiv:2011.08780]**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]**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

npj 2D Materials and Applications 7, 47 (2023) [arXiv:2001.01735]**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]**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]**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)**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]**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]**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]**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]**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]**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]**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]**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]**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]**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]**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]**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]**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]**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]**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]**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]**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]**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]**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]**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]**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]**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]**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

**Faseovergangen door quantumonzekerheid**

Jins de Jong, Lennert van Tilburg en Erik van Loon

Nederland Tijdschrift voor Natuurkunde, november 2012