Systems of interest: single-level quantum dots with local Coulomb interaction connected to metallic and superconducting (BCS) leads
that can be described by the superconducting impurity Anderson model Methods: second order perturbation theory in Coulomb interaction stregth, numerical renormalization group (NRG),
CT-HYB quantum Monte Carlo Goal: consistent description of the behavior of the subgap Andreev bound states (Yu-Shiba-Rusinov states) and the Josephson current
in the vicinity of the single-doublet (zero-pi) quantum phase transition
SQUAD - SUperconducting QUAntum Dot
- set of python scripts to calculate properties of these systems using the diagrammatic
second order perturbation method
code to calculate properties of these systems using the CT-HYB quantum Monte-Carlo method
Systems of interest: spinful molecules attached to metallic or insulating substrates or leads Methods: density functional theory (DFT), non-equilibrium Green functions (NEGF) Goal: search for molecular systems suitable as building elements of molecular spintronic devices
Thermodynamically consistent description of quantum criticality
We are developing methods based on diagrammatic perturbation techniques to study
quantum criticality in interacting electron systems described by lattice models (e.g. Anderson or Hubbard model).
Methods are based on the parquet construction of two-particle functions and provide a consistent description
that is free of unphysical symmetry breaking and does not violate conservation laws.
Poster from the 2017 summer school in Tallahassee (pdf)
SPEpy - Simplified Parquet Equations in python
- set of python scripts to calculate properties of the single-impurity Anderson model using the
simplified parquet equation solver
Correlated materials with strong spin-orbit interactions
We use the combination of ab-initio (LDA) methods and dynamical mean-field theory (DMFT)
to study materials
with strong effect of spin-orbit coupling on their electronic and magnetic properties. The focus lies on transition-metal
oxides with heavy ions such as iridium and osmium. We use the continuous-time quantum Monte-Carlo method in the
strong-coupling limit (CT-HYB) to solve the underlying impurity problem.
Correlated electrons in disordered alloys (PhD thesis)
We developed methods to calculate charge transport in disordered systems of elastically
scattered electrons. These diagrammatic methods are based on an asymptotic limit to high spatial dimensions
and utilize advanced diagram summation techniques on the two-particle level. They allow us to calculate
electrical conductivity and diffusion coefficient for arbitrary disorder strength.
The numerical calculations are performed on the disordered Anderson model and the Falicov-Kimball model.
Critical properties of the mixed-spin Heisenberg model (Master thesis)
We studied the critical properties of the anisotropic mixed spin-1 and spin-1/2
quantum Heisenberg model using a simple two-site mean-field approximation. We treat in detail the system
on the simple cubic lattice considering both exchange anisotropy and uniaxial singe-ion anisotropy.
The critical behavior is analysed and the complete phase diagrams were calculated, where aside from the
typical ferromagnetic phase a low-temperature quantum ordered phase is described.