dr. Erik G. C. P. van Loon  
evloon at itp dot unibremen dot de  
Room  NW1 O3040 
OttoHahnAllee 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 MeanField 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 singlesite reference model. This approach has been hugely successful at describing the oneparticle properties of correlated models (Hubbard model) and materials: for example, the density of states, selfenergy and spectral function. As a nonperturbative 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, chargedensity waves, etc. These used to be too difficult to accurately determine computationally, due to a difference in length scales. The DMFT approach knows about onsite correlations, but not about momentum dependence and long wavelengths. These aspect are necessary for determining the dispersion of collective modes (plasmons, magnons and zerosound modes) as well as for investigating chargedensity 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 socalled 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 electronelectron and electronphonon interaction in NbS2.
Publications

2101.01140

A full gap above the Fermi level: the charge density wave of monolayer VS_{2}

An efficient fluctuation exchange approach to lowtemperature spin fluctuations and superconductivity: from the Hubbard model to Na_{x}CoO_{2}⋅yH_{2}O

Secondorder dual fermion for multiorbital systems

The BetheSalpeter equation at the critical endpoint of the Mott transition

Coulomb Engineering of twodimensional Mott materials

Turbulent hydrodynamics in strongly correlated Kagome metals

Abinitio phonon selfenergies and fluctuation diagnostics of phonon anomalies: lattice instabilities from Dirac pseudospin physics in transitionmetal dichalcogenides

Environmental control of charge density wave order in monolayer 2HTaS_{2}

Thermodynamics of the metalinsulator transition in the extended Hubbard model

Dual Boson approach with instantaneous interaction

Bandwidth renormalization due to the intersite Coulomb interaction

Twoparticle Fermi liquid parameters at the Mott transition: Vertex divergences, Landau parameters, and incoherent response in dynamical meanfield theory

Fermionboson vertex within Dynamical MeanField Theory

Secondorder dual fermion approach to the Mott transition in the twodimensional Hubbard model

Confining graphene plasmons to the ultimate limit

Firstorder metalinsulator transitions in the extended Hubbard model due to selfconsistent screening of the effective interaction

Precursors of the insulating state in the squarelattice Hubbard model

The extended Hubbard model with attractive interactions

Competing Coulomb and electron–phonon interactions in NbS_{2}

Conservation in twoparticle selfconsistent extensions of dynamicalmeanfieldtheory

A comparison between methods of analytical continuation for bosonic functions

From local to nonlocal correlations: The Dual Boson perspective

Capturing nonlocal interaction effects in the Hubbard model: optimal mappings and limits of applicability

Interactiondriven Lifshitz transition with dipolar fermions in optical lattices

Double occupancy in dynamical meanfield theory and the Dual Boson approach

Selfconsistent Dual Boson approach to singleparticle and collective excitations in correlated systems

Ultralongrange order in the FermiHubbard model with longrange interactions

Thermodynamic consistency of the charge response in dynamical meanfield based approaches

Beyond extended dynamical meanfield theory: Dual boson approach to the twodimensional extended Hubbard model

Plasmons in Strongly Correlated Systems: Spectral Weight Transfer and Renormalized Dispersion

Collective charge excitations of strongly correlated electrons, vertex corrections, and gauge invariance
Popular Publications

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