On the Imbalanced d-wave Superfluids within the Spin Polarized Extended Hubbard Model: Weak Coupling Limit

We investigate the superfluid properties of d-wave pairing symmetry within the Extended Hubbard Model (EHM) in a magnetic field. We analyze the temperature and magnetic field dependencies of the order parameter. We find that in the two-dimensional case, the spatially homogeneous spin polarized superfluidity ($SC(P\neq0)$) is stable in the weak coupling limit, at T=0, as opposed to the s-wave pairing symmetry case in 2D. We construct the ground state phase diagrams both for fixed chemical potential ($\mu$) and electron concentration ($n$). Furthermore, we obtain the temperature vs. magnetic field and temperature vs. spin polarization phase diagrams.Comment: 5 pages, 3 figure

On the BCS-BEC crossover in the 2D Asymmetric Attractive Hubbard Model

We analyze the evolution from the weak coupling (BCS-like limit) to the strong coupling limit of tightly bound local pairs (LP's) in the 2D asymmetric attractive Hubbard model, in the presence of the Zeeman magnetic field ($h$). The broken symmetry Hartree approximation is used. We also apply the Kosterlitz-Thouless (KT) scenario to determine the phase coherence temperatures. We obtain that for the spin dependent hopping integrals ($t^{\uparrow}\neq t^{\downarrow}$) the homogeneous polarized superfluid (SC$_M$) phase in the ground state for the strong attraction and lower filling can be stabilized. We find a topological quantum phase transition (Lifshitz type) from the unpolarized superfluid phase (SC$_0$) to SC$_M$ and tricritical point in the ($h-\mu$) and spin polarization ($P$) vs. attraction ($U<0$) ground state phase diagrams. The finite temperatures phase diagrams for $t^{\uparrow}\neq t^{\downarrow}$ are constructed.Comment: 4 pages, 3 figures, proceedings of the international conference Physics of Magnetism 2011, Poznan, Polan

Lattice Hamiltonian approach to the Schwinger model: further results from the strong coupling expansion

We employ exact diagonalization with strong coupling expansion to the massless and massive Schwinger model. New results are presented for the ground state energy and scalar mass gap in the massless model, which improve the precision to nearly $10^{-9}$. We also investigate the chiral condensate and compare our calculations to previous results available in the literature. Oscillations of the chiral condensate which are present while increasing the expansion order are also studied and are shown to be directly linked to the presence of flux loops in the system.Comment: 7 pages, 6 figures, to appear in PoS(Lattice 2014)31