Benjamin LENZ

Post Doctoral Fellow

Research group: Condensed Matter

Research interests:

My research focusses on elaborating predictive electronic structure techniques for materials with strong electronic correlations. In these systems, the strong Coulomb interactions between the electrons of the solid ask for augmenting electronic structure calculations by state-of-the-art many-body theoretical techniques.
To this end, I am deriving effective low-energy electron models from ab-initio density functional theory calculations, which I subsequently solve by means of quantum cluster methods and dynamical mean-field theories.

Currently I am investigating the effects of short-range antiferromagnetic fluctuations on the electronic structure of iridates, e.g. Sr2IrO4, where the interplay of Coulomb and spin-orbit interactions lead to an intricate entangled ground state.
Besides the effects of non-local fluctuations, I am particularly interested in the effect of long-range Coulomb interactions and many-body screening on the electronic structure of these correlated materials.

I am also interested in the dimensional crossover between one and two dimensions and its effects on the Mott metal-insulator transition. Tuning the anisotropy of the hopping in the spatial directions can for instance trigger a quantum phase transition, which asks questions on the criticality class.
Furthermore, I have also worked on a paradigmatic model for heavy-fermion systems, the two-dimensional Kondo lattice model, where the interplay of antiferromagnetism, Kondo screening and superconductivity lead to a rich phase diagram.


Phone number +33(0) 1 69 33 42 90
Address CPHT, Ecole Polytechnique, 91128 Palaiseau cedex, France
Office 'Aile 0', office 1011


PhD Thesis : "Unconventional phases in two-dimensional Hubbard and Kondo-lattice models by variational cluster approaches", supervised by Prof. Dr. Thomas Pruschke (deceased) and PD Dr. Salvatore R. Manmana (University of Göttingen)

Publications :

A. Louat, B. Lenz, S. Biermann, C. Martins, F. Bertran, P. Le Fèvre, J. E. Rault, F. Bert, and V. Brouet
ARPES study of orbital characters, symmetry breakings and pseudogaps in doped and pure Sr2IrO4
arXiv: 1907.01247 (2019)

J. Jeong, B. Lenz, A. Gukasov, X. Fabreges, A. Sazonov, V. Hutanu, A. Louat, C. Martins, S. Biermann, V. Brouet, Y. Sidis, and P. Bourges
Magnetization density distribution of Sr2IrO4: Deviation from a local jeff=1/2 picture
arXiv: 1904.09139 (2019)

B. Lenz, C. Martins, and S. Biermann
Spectral functions of Sr2IrO4: Theory versus experiment

J. Phys.: Condens. Matter 31 293001 (2019)
DOI: 10.1088/1361-648X/ab146a 

C. Martins, B. Lenz, L. Perfetti, V. Brouet, F. Bertran, and S. Biermann
Non-local Coulomb correlations in pure and electron-doped Sr2IrO4: Spectral functions, Fermi surface and pseudogap-like spectral weight distributions from oriented cluster dynamical mean-field theory
Phys. Rev. Mat. 2 032001(R) (2018)
DOI: 10.1103/PhysRevMaterials.2.032001

G. Ehlers, B. Lenz, S. R. Manmana, and R. M. Noack
Anisotropy crossover in the frustrated Hubbard model on four-chain cylinders
Phys. Rev. B 97 035118 (2018)
DOI: 10.1103/PhysRevB.97.035118

B. Lenz, R. Gezzi, and S. R. Manmana
Variational cluster approach to superconductivity and magnetism in the Kondo lattice model
Phys. Rev. B 96 155119 (2017)
DOI: 10.1103/PhysRevB.96.155119

B. Lenz, S. R. Manmana, T. Pruschke, F. F. Assaad, and M. Raczkowski
Mott quantum criticality in the anisotropic 2D Hubbard model
Phys. Rev. Lett. 116 086403 (2016)
DOI: 10.1103/PhysRevLett.116.086403