| dc.contributor.advisor | Pruschke, Thomas Prof. Dr. | |
| dc.contributor.author | Bodensiek, Oliver | |
| dc.date.accessioned | 2013-10-11T08:45:52Z | |
| dc.date.available | 2013-10-11T08:45:52Z | |
| dc.date.issued | 2013-10-11 | |
| dc.identifier.uri | http://hdl.handle.net/11858/00-1735-0000-0001-BBE3-3 | |
| dc.identifier.uri | http://dx.doi.org/10.53846/goediss-4086 | |
| dc.identifier.uri | http://dx.doi.org/10.53846/goediss-4086 | |
| dc.identifier.uri | http://dx.doi.org/10.53846/goediss-4086 | |
| dc.language.iso | eng | de |
| dc.rights.uri | http://creativecommons.org/licenses/by-nc-nd/3.0/ | |
| dc.subject.ddc | 530 | de |
| dc.title | Superconductivity and Antiferromagnetism in the Kondo-Lattice Model | de |
| dc.type | doctoralThesis | de |
| dc.contributor.referee | Pruschke, Thomas Prof. Dr. | |
| dc.date.examination | 2013-08-15 | |
| dc.subject.gok | Physik (PPN621336750) | de |
| dc.description.abstracteng | In this thesis, antiferromagnetic and superconducting order in the Kondo-lattice model is investigated by means of the dynamical mean-field theory (DMFT) in combination with the numerical renormalization group (NRG) method. First, these numerical methods are introduced and a special emphasis is put on the inclusion of superconducting order by employing the Nambu formalism. In the next chapter, the Kondo-lattice model as a paradigmatic model for heavy-fermion system is introduced. The analysis of the paramagnetic state at zero temperature reviews the description of the electronic system as a Fermi liquid of heavy quasiparticles. Afterwards ordered phases are investigated.
In the antiferromagnetically ordered phase at zero temperature and half filling, a Néel state is found to be stable for small Kondo interactions. A peculiar feature arises in the density of states: A “spin resonance” is observed at energies which scale with the Kondo coupling. These resonances are the more pronounced, the higher the conduction band electrons are polarized – hence they are quite likely related to spin fluctuations.
As a main result of the thesis, a superconducting state at zero temperature is found to be stable in a large parameter regime within the DMFT+NRG approach. The pair correlations are the most pronounced in the region of the parameter space, where AF order breaks down. Although only even-frequency singlet s-wave superconductivity can be treated within the utilized approach, the superconducting state is actually found to be closely related to local spin fluctuations, which act as retarded “glue” for s-wave pairing of heavy quasiparticles. This is a novel mechanism for superconductivity in HF systems. Similar to the antiferromagnetic case, resonances are observed in the density of states at energies related to the spin-fluctuation spectrum. These resonances are interpreted by means of a static mean-field description as a separation of the flat quasiparticle bands from the strongly dispersive part of the bandstructure. Such a structure is also observed in the spectral functions obtained by DMFT. Therefore, the conclusion is drawn that the pairing appears among the heavy quasiparticles. This conclusion is underpinned by sign changes of the dynamic gap function at the very frequencies, where the resonances respectively the band splitting is observed. In addition, the observed rule that the critical temperature for the superconducting state is generally lower than the coherence scale, indicates that the heavy-fermion state is a prerequisite for pairing in the Kondo-lattice model. Moreover, the ratio of the gapwidth and critical temperature is strongly enhanced over the universal BCS ratio. This fact is associated with a non-phononic origin of the attractive interaction. In summary, the stable superconducting state in the Kondo-lattice model is identified to be highly unconventional. | de |
| dc.contributor.coReferee | Vojta, Matthias Prof. Dr. | |
| dc.subject.eng | Kondo lattice | de |
| dc.subject.eng | superconductivity | de |
| dc.subject.eng | correlated | de |
| dc.subject.eng | electrons | de |
| dc.subject.eng | antiferromagnetism | de |
| dc.subject.eng | heavy fermion superconductivity | de |
| dc.identifier.urn | urn:nbn:de:gbv:7-11858/00-1735-0000-0001-BBE3-3-7 | |
| dc.affiliation.institute | Fakultät für Physik | de |
| dc.identifier.ppn | 769803407 | |