Dr. Agnieszka Cichy
I'm a condensed matter theoretical physicist. I am
interested in several research areas, including: spin-polarized superfluidity (with population imbalance), Bose-Fermi mixtures, mixtures of fermions with unequal masses, mixtures of fermions with three hyperfine states as well as orbital magnetism. These topics certainly belong to the frontiers of contemporary condensed matter physics. One of the most interesting directions is, in my opinion, the interface between condensed matter theory and other branches of theoretical physics,
in particular quantum field theory. I have also performed research in lattice field theory. Personally, I'm a happy wife of Krzysztof (who is also a theoretical physicist) and a mom of Filip.
Strongly correlated systems
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Ultracold atomic gases
RESEARCH DIRECTIONS
Lattice QCD
MY LATEST RESEARCH
We study superconducting properties of population-imbalanced ultracold Fermi mixtures in the honeycomb lattice that can be effectively described by the spin-imbalanced attractive Hubbard model in the presence of a Zeeman magnetic field. We use the mean-field theory approach to obtain ground-state phase diagrams including the unconventional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, which is characterized by atypical behavior of the Cooper-pair total momentum. We show that the momentum changes its value as well as direction with a change of the system parameters. We discuss the influence of Van Hove singularities on the possibility of the reentrant FFLO phase occurrence, without a BCS precursor.
By means of dynamical mean-field theory allowing for complete account of SU(2) rotational symmetry of interactions between spin-1/2 particles, we observe a strong effect of suppression of ferromagnetic order in the multiorbital Fermi-Hubbard model in comparison with a widely used restriction to density-density interactions. In the case of orbital degeneracy, we show that the suppression effect is the strongest in the two-orbital model (with effective spin Seff=1) and significantly decreases when considering three orbitals (Seff=3/2), thus magnetic ordering can effectively revive for the same range of parameters, in agreement with arguments based on vanishing of quantum fluctuations in the limit of classical spins (Seff→∞). We analyze a connection to the double-exchange model and observe high importance of spin-flip processes there as well.
We study the superconducting properties of population-imbalanced ultracold Fermi mixtures in one-dimensional optical lattices that can be effectively described by the spin-imbalanced attractive Hubbard model in the presence of a Zeeman magnetic field. We use the mean-field theory approach to obtain the ground-state phase diagrams including some unconventional superconducting phases such as the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, and the η phase (an extremal case of the FFLO phase), both for the case of a fixed chemical potential and for a fixed number of particles. It allows us to determine optimal regimes for the FFLO phase as well as η-pairing stability. We also investigate the evolution from the weak coupling (BCS-like limit) to the strong coupling limit of tightly bound local pairs (BEC) with increasing attraction, at T=0. Finally, the obtained results show that in spite of the occurrence of the Lifshitz transition induced by an external magnetic field, the superconducting state can still exist in the system, at higher magnetic field values.