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Tunneling Current into the Vortex Lattice States of s- and p-Wave Superconductors

100%
Kowalewski L., Nogala M., Thomas M., Wojciechowski R.
Acta Physica Polonica A
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2000
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vol. 97
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issue 1
237-240
EN
The tunneling current between the metallic tip of a scanning microscope and s-wave and p-wave superconductors in a quantizing magnetic field is investigated. The differential conductance is calculated both as a function of bias voltage at the centre of the vortex line and for varying position of the scanning tunneling microscope tip at a stable voltage.
2
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Heavy Fermion Superconductor Order Parameter in High Magnetic Field

100%
Kowalewski L., Wojciechowski R., Thomas M., Nogala M.
Acta Physica Polonica A
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1994
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vol. 85
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issue 2
347-350
EN
It is shown that, independently on either the nature and the strength of pairing, the orbital effects of a high magnetic field in heavy fermion superconductor change the form of both the effective pairing and the gap function.
3
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Effects of Frustrating Hopping on Charge Ordered States in Itinerant Fermion Systems for Arbitrary Concentration in 2D Lattice

100%
Czart W., Grzybowski P., Nogala M., Robaszkiewicz S.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
828-831
EN
There is ongoing, intense, research in the field of electron charge orderings (CO) and charge density waves phenomena, due to experimental discovery of such phases in numerous important compounds. The aim of this work is to extend recent advances in the field by studying two simple effective paradigmatic models used to describe CO in narrow band materials i.e. (i) a model of correlated electrons: the so-called t-W model of spinless fermions with repulsive interaction W and (ii) the molecular crystal model with the coupling of electrons to intramolecular (crystal field) vibrations in the static limit. The finite temperature phase diagrams are evaluated at arbitrary carriers concentration for several representative cases. Our calculations are performed within the (broken symmetry) HFA for d=2 square lattice and arbitrary carriers concentration. In this contribution we focus on the effects of next-nearest-neighbor hopping on the CO states in these systems and the problem of phase separations involving checkerboard CO with the nesting vector Q=(π,π). The results we show here are an extension of our previous work on the subject.
4
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Tunneling Charge Transport in Graphene-Based Superconductor Junctions

100%
Wojciechowski R., Kowalewski L., Nogala M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1092-1094
EN
We study the spin polarized electron and hole tunneling transport through a graphene-based ferromagnet(GF_1)-insulator(GI_1)-superconductor(G_{S})-insulator(GI_2)-ferromagnet(GF_2) junction. Proximity induced spin polarization and superconductivity in a graphene sheet are assumed to be created by superconducting and ferromagnetic electrodes placed on the top of the graphene. Using a four-dimensional version of the Dirac-Bogoliubov-de Gennes equation with appropriate boundary conditions we investigate the tunneling processes through the junctions. In particular, we present calculations of the amplitudes of normal and Andreev reflections as a function of the energy of the incident electron for a wide range of the model parameters, such as the strength and orientation of the exchange field, the barrier strength, and the distance between the two ferromagnetic layers. The tunneling transport processes in the graphene-based double junction GF/GI/G_{S}/GI/GF are compared with those in non-graphene-based junctions.
5
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Charge Orderings and Phase Separations in Itinerant Fermion Systems at Half Filling

100%
Czart W., Grzybowski P., Nogala M., Robaszkiewicz S.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1042-1044
EN
We analyse the ground state phase diagrams of the charge orderings in narrow band materials using two effective models: (1) the spinless fermion model (t - W) with repulsive intersite interaction (W_{ij} > 0) and (2) the molecular crystal model with the coupling of electrons to intramolecular (crystal field) vibrations. We present results for the case of half filled bands for d = 2 square lattice. The calculations are performed within the (broken symmetry) Hartree-Fock approximation. The study takes into consideration the effects of frustrating next-nearest-neighbour hopping (t_2) on the charge ordered states in these systems. We focus on the two cases: (i) homogeneous phases and phase separations involving checkerboard charge ordering with the nesting vector Q= (π,π) only and (ii) homogeneous phases and phase separations involving two types of charge ordering: (a) checkerboard charge ordering with the nesting vector Q = (π,π), and (b) collinear (CL) charge ordering with Q = (0,π) or Q = (π,0).
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