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1

Asymmetric Tunneling Conductance in Doped Antiferromagnets

100%

Maciąg A., Wróbel P.

Acta Physica Polonica A

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2006

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vol. 109

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issue 4-5

607-610

EN

We calculate the tunneling conductance in the framework of the spin polaron model, which is an effective model for the t-J model, in the limit where at least short-range antiferromagnetic correlations exist. We show that both in the normal state and in the superconducting state the asymmetry of tunneling conductance is present. This fact is the implication of the particle-hole asymmetry of the spin polaron Hamiltonian in the limit of low density of spin polarons which are quasiparticles emerging in a hole doped antiferromagnet. Experimental evidence of analogous asymmetric tunneling conductance was found in the tunneling spectroscopy measurements of high T_c superconductors.

2

Influence of Electronic Structure on the Phase Diagram of Weakly Doped Superconducting Cuprates

100%

Maciąg A., Wróbel P.

Acta Physica Polonica A

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2007

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vol. 111

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issue 5

721-725

EN

Motivated by the difference between the experimental phase diagram of cuprates and expectations of the t-J model, we analyze the influence of the electronic structure on superconducting state generation for small levels of doping. Following some theoretical studies of the Fermi surface for hole doped superconducting cuprates we base our calculations on the t-t'-t''-J model. We construct the spin polaron model, which is an effective model for the t-J model, and we expand it by adding the new terms related to the next neighbor hopping integrals t' and t''. In the framework of this model we study evolutions of superconducting correlation functions with doping. As a result of numerical calculations we find out that superconducting state vanishes for small levels of doping and finite values of t' and t''. This is in qualitative agreement with experimental results.

3

Spin Polaron-Bipolaron Scenario of Three Gap-Like Energy Scales in Superconducting Cuprates

71%

Wróbel P., Maciąg A., Suleja W., Eder R., Micnas R.

Acta Physica Polonica A

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2010

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vol. 118

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issue 2

292-298

EN

We argue that three gaps observed in underdoped cuprates can be attributed to the formation of antiferromagnetic spin polarons and bipolarons. Within the spin polaron scenario the antinodal pseudogap at he high energy scale originates from the change of the Fermi surface topology, induced by antiferromagnetic correlations. That change gives rise to the diminishing of the spectral weight at the antinodal region near the Brillouin zone boundary. We demonstrate that effect by analyzing effective models of doped antiferromagnets. The second type of pseudogap appearing at the intermediate energy scale originates from the phenomena which are precursory to superconductivity and predominantly concern the portion of the Fermi surface near the nodal region. In order to analyze the latter phenomenon we use the negative U Hubbard model, in which many details typical to spin polaron physics are neglected, but which contains the essential ingredient of it, that is the strong short range attraction. The lowest energy scale is related to the true superconducting gap which develops with doping, although both types of pseudogap diminish with doping. This behavior can be explained by the fact that the spin polaron band is empty in the undoped system and therefore the formation of the superconducting state in the system is forbidden. Due to a pedagogical character of this report, we present in the introduction a short overview of mostly recent experimental results which are related to the gap-pseudogap physics.

4

Unconventional Superconductivity, Spontaneous Time-Reversal Symmetry Breaking and Lowering of Kinetic Energy in Doped, Short-Range Antiferromagnets

71%

Wróbel P., Maciąg A., Eder R., Fulde P., Micnas R.

Acta Physica Polonica A

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2004

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vol. 106

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issue 5

575-581

EN

In this paper we focus on the anomalous temperature dependence of the in-plane conductivity and symmetry mixing of the superconducting order parameter observed in various experiments on cuprates. We show that the one-band Hubbard model is not capable of describing the physics of cuprates because the kinetic energy is lowered in this model in the superconducting state, which contradicts experimental observations. The proper model to investigate doped, short-range antiferromagnets is the t-J model, for which our results agree with experiments. We analyze a spin polaron model, that is an effective model for a doped antiferromagnet. In the framework of this model we also study the superconducting order-parameter symmetry-mixing phenomenon. We show that the expected mixing of d-wave symmetry with p-wave symmetry takes place in the superconducting order-parameter at a finite value of the doping parameter. This symmetry mixing brakes the time-reversal symmetry.

Refine search results

4 Acta Physica Polonica A

1 2010

1 2007

1 2006

1 2004

4 Maciąg A.

4 Wróbel P.

2 Eder R.

2 Micnas R.

1 Fulde P.

1 Suleja W.

Asymmetric Tunneling Conductance in Doped Antiferromagnets

Influence of Electronic Structure on the Phase Diagram of Weakly Doped Superconducting Cuprates

Spin Polaron-Bipolaron Scenario of Three Gap-Like Energy Scales in Superconducting Cuprates

Unconventional Superconductivity, Spontaneous Time-Reversal Symmetry Breaking and Lowering of Kinetic Energy in Doped, Short-Range Antiferromagnets