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Superconductivity in the Penson-Kolb Model on a Triangular Lattice

100%
Ptok A., Mierzejewski M.
Acta Physica Polonica A
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2008
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vol. 114
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issue 1
209-212
EN
We investigate properties of the two-dimensional Penson-Kolb model with repulsive pair hopping interaction. In the case of a bipartite square lattice this interaction may lead to the eta-type pairing, when the phase of superconducting order parameter changes from one lattice site to the neighboring one. We show that this interaction may be responsible for the onset of superconductivity also for a triangular lattice. We discuss the spatial dependence of the superconducting order parameter and demonstrate that the total momentum of the paired electrons is determined by the lattice geometry.
2
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Inhomogeneous Charge Distribution and Superconductivity in the Boson-Fermion Model

100%
Śledź Ż., Mierzejewski M.
Acta Physica Polonica A
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2008
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vol. 114
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issue 1
219-223
EN
We analyze a boson-fermion model that accounts for the electrostatic potential of the out-of-plane dopant atoms. We investigate whether this approach may explain recent experimental results obtained for the Bi-based high-temperature superconductors. We demonstrate that in contradistinction to purely fermionic models, even weak electrostatic potential of the dopant atoms may be responsible for a significant modulation of the superconducting order parameter.
3
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Pseudogap and Vortices in High-Temperature Superconductors

100%
Maśka M., Mierzejewski M.
Acta Physica Polonica A
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2004
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vol. 106
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issue 5
569-574
EN
The origin of the pseudogap is one of the most puzzling features of the high-temperature superconductors. There are two main scenarios: the first one assumes the presence of a hidden order competing or coexisting with superconductivity; within the framework of the second one the pseudogap is a precursor of the superconducting gap. In this paper we present some aspects of the hidden order pseudogap scenario. In particular, we discuss how the competing order modifies the structure of vortices in high-temperature superconductors. We demonstrate that the presence of the hidden order can explain some features of vortices observed in scanning tunneling microscopy experiments.
4
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Vortex Properties in a Model with Local Pairs

81%
Śledź Ż., Mierzejewski M., Maśka M.
Acta Physica Polonica A
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2006
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vol. 109
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issue 4-5
653-656
EN
We investigate the vortex structure in the Penson-Kolb model with and without impurities. We focus on the consequences arising from the non-local field-dependent pairing interaction for the vortex profile, current distribution, and the local density of states.
5
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Upper Critical Field for Cobalt Oxide Superconductors

81%
Mierzejewski M., Maśka M., Andrzejewski B.
Acta Physica Polonica A
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2004
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vol. 106
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issue 5
603-608
EN
Motivated by the recent discovery of the cobalt oxide superconductors, we calculate the temperature dependence of the upper critical field on a triangular lattice. Using the lattice version of the Gor'kov equations we investigate how the applied magnetic field affects singlet and triplet types of superconductivity. We show that in a wide range of model parameters not only Zeeman coupling, but also the diamagnetic pair breaking mechanism favors the triplet pairing. In the cobalt oxide superconductors the symmetry of the order parameter remains an open problem and both singlet and triplet superconductivity should be taken into account. We show that in such a case, an external magnetic field may induce a transition from singlet to triplet superconductivity. We discuss experimental results which may confirm this tempting hypothesis.
6
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Charge Density Waves in Small Metallic and Superconducting Rings

81%
Maśka M., Czajka K., Mierzejewski M., Śledź Ż.
Acta Physica Polonica A
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2006
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vol. 109
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issue 4-5
519-525
EN
Experimental results concerning persistent currents in small rings threaded by a magnetic flux do not agree with theoretical predictions, especially for experiments performed in diffusive regime. This suggests important role of disorder in these experiments. In this paper we demonstrate how impurities present in ring modify the persistent current by generating or enhancing charge density waves. The electronic correlations are taken into account for both repulsive as well as attractive electron-electron interaction. The calculations are carried out for one-dimensional rings consisting of up to 12 lattice sites using Lanczös exact diagonalization approach, and for finite-width much larger rings using the Bogolyubov-de Gennes equations.
7
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Doped Carrier Formulation of the t-J model: Monte Carlo Study of the Anisotropic Case

81%
Ferraz A., Kochetov E., Maśka M., Mierzejewski M.
Acta Physica Polonica A
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2008
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vol. 114
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issue 1
185-189
EN
We derive a doped carrier representation of the t-J model Hamiltonian. Within this approach the t-J model is described in terms of holes hopping in a lattice of correlated spins, where holes are the carriers doped into the half-filled Mott insulator. This representation of the t-J Hamiltonian is very convenient for underdoped systems since close to half-filling it allows for a controlled treatment of the crucial constraint of no doubly occupied sites. When neglecting the transverse spin-spin interaction, the effective Hamiltonian can be investigated with classical Monte Carlo simulations. We discuss the results obtained for systems consisting of several hundred lattice sites.
8
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The Falicov-Kimball Model in External Magnetic Field: Orbital Effects

81%
Wróbel M., Mierzejewski M., Maśka M.
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issue 2
379-382
EN
We study thermodynamic properties of the two-dimensional (2D) Falicov-Kimball model in the presence of external magnetic field perpendicular to the lattice. The field is taken into account by the Peierls substitution in the hopping term. We show how the Hofstadter butterfly is affected by electronic correlations. In the non-interacting case the field dependent energy spectrum forms the famous Hofstadter butterfly. Our results indicate that for arbitrary nonzero interaction strength and arbitrary magnetic field there is a gap in the energy spectrum at sufficiently low temperature. The gap vanishes with increase of temperature for weak coupling, however, it persists at high temperatures if the coupling is strong enough. Numerical results have been obtained with the help of Monte Carlo technique based on a modified Metropolis algorithm.
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