Transporttheorie für geordnete und ungeordnete Systeme schwerer Fermionen

Heavy-fermion systems (HFS, several lanthanide or actinide compounds) exhibit a linear coefficient of the low-temperature specific heat that is much larger than in usual metals, and this enhancement is usually attributed to quasiparticles with a very large effective mass. The essential features of HFS are based on the interplay of localised, strongly correlated f electrons with broad conduction bands as described by the periodic Anderson model (PAM). We investigate the temperature dependence of the transport properties of HFS (e.g. resistivity, thermoelectric power) in the linear-response regime (using Kubo formulae and the Jonson-Mahan theorem).In the dynamical mean-field theory (DMFT), the PAM is mapped on an effective single-impurity model. As impurity solvers we use both Wilson's numerical renormalization group and the modified perturbation theory. In addition, we explore the influence of substitutional disorder on the transport properties of HFS by an extension of the DMFT to a coherent-potential approximation for disordered strongly-correlated electron systems (PAM with random potentials). The typical experimental results are reproduced, in particular the temperature and concentration dependence of the resistivity and the thermoelectric power and their absolute magnitude for both metallic HFS and Kondo insulators.Finally, we examine four different estimates for possible characteristic low-temperature scales of the PAM without disorder. The results indicate that there is only one relevant scale; we get a one-parameter scaling of thermodynamic and some transport properties with a strongly occupancy-dependent scaling function.Also published by Mensch-und-Buch-Verlag Berlin 2008, ISBN 978-3-86664-504-2.See also corresponding articles:DOI 10.1103/PhysRevB.74.195119DOI 10.1103/PhysRevB.77.11512

Transport Theory for Ordered and Disordered Heavy-Fermion Systems

Heavy-fermion systems (HFS, several lanthanide or actinide compounds) exhibit a linear coefficient of the low-temperature specific heat that is much larger than in usual metals, and this enhancement is usually attributed to quasiparticles with a very large effective mass. The essential features of HFS are based on the interplay of localised, strongly correlated f electrons with broad conduction bands as described by the periodic Anderson model (PAM). We investigate the temperature dependence of the transport properties of HFS (e.g. resistivity, thermoelectric power) in the linear-response regime (using Kubo formulae and the Jonson-Mahan theorem).In the dynamical mean-field theory (DMFT), the PAM is mapped on an effective single-impurity model. As impurity solvers we use both Wilson's numerical renormalization group and the modified perturbation theory. In addition, we explore the influence of substitutional disorder on the transport properties of HFS by an extension of the DMFT to a coherent-potential approximation for disordered strongly-correlated electron systems (PAM with random potentials). The typical experimental results are reproduced, in particular the temperature and concentration dependence of the resistivity and the thermoelectric power and their absolute magnitude for both metallic HFS and Kondo insulators.Finally, we examine four different estimates for possible characteristic low-temperature scales of the PAM without disorder. The results indicate that there is only one relevant scale; we get a one-parameter scaling of thermodynamic and some transport properties with a strongly occupancy-dependent scaling function.Also published by Mensch-und-Buch-Verlag Berlin 2008, ISBN 978-3-86664-504-2.See also corresponding articles:DOI 10.1103/PhysRevB.74.195119DOI 10.1103/PhysRevB.77.11512