Supercondutividade e magnetismo em pnictídeos baseados em ferro no formalismo do grupo de renormalização até dois loops
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Data
2012-04-04
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Universidade Federal de Goiás
Resumo
We study the low-energy properties of a two-band model by means of the eld-theoretical
renormalization group (RG) up to two loops in order to describe some iron-based pnictide superconductors.
Initially, we reproduce some known results of the RG up to one loop to show
how one should proceed with the eld-theoretical RG. We then calculate the self-energy of the
model and the irreducible four-point vertex functions ��(4) up to two loops. We derive the RG
equations for the couplings and the quasiparticle weight of the model at this order of approximation.
Following a similar procedure, we show how to determine the possible instabilities
of the ground state of the model and the nature of the low-energy elementary excitations by
calculating the RG
ow equations up to two loops for the extended s-wave (s ) and conventional
s-wave (s++) superconducting susceptibilities, charge and spin density wave susceptibilities
and also the uniform charge and spin susceptibilities. The numerical analysis of these equations
reveals that the couplings of the two-band model are divergent in the low-energy limit, but their
ratio
ows to a xed point. We obtain, by means of this analysis, that the antiferromagnetic
instability is the dominant one, whereas the superconducting instability is the second most
important instability. We show that the superconducting instability of s -type exceeds the
s++-type when the Umklapp interaction is present and may overcome the antiferromagnetic
instability for some doping value in the system. The numerical solution for the quasiparticle
weight reveals that this quantity is always close to its initial value during the renormalization
procedure of the model, while the uniform charge and spin susceptibilities remain nite for the
energy scales where the RG approach up to two loops is valid. These results are consistent with
the interpretation that the normal state of that model is, in fact, described by Landau's Fermi
liquid theory with well-de ned quasiparticle excitations in the low-energy limit.
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CARVALHO, Vanuildo Silva de. Supercondutividade e magnetismo em pnictídeos baseados em ferro no formalismo do grupo de renormalização até dois loops. 2012. 106 f. Dissertação (Mestrado em Fisica) - Universidade Federal de Goiás, Goiânia, 2012.