| Sr2RuO4 superconductor is a kind of superconductor with the same structure as La2 CuO4,and it is likely to be a chiral p-wave superconductor.However,there are still widespread disputes about the pairing symmetry of Sr2 RuO4.The experiments of spin polarized neutron scattering,muon spin relaxation and early nuclear magnetic resonance(NMR)show that Sr2 RuO4 is chiral pwave triplet pairing.while in the experiments of specific heat,superfluid density and thermal conductivity,it is observed that there are nodes in the energy gap,which is the typical characteristics of d-waves.In this paper,we use the functional renormalization group(FRG)method to study the three orbit model of Sr2 RuO4,and consider the influence of spin orbit coupling(SOC).Our results can explain the dispute that the p-wave behaves like the d-wave.Then we analyze and discuss our results with related experiments.The whole thesis is composed by six chapters.Chapter 1: In this chapter,we mainly introduce the history of superconductivity and superconductive materials,and make a basic introduction to the superconductive material Sr2 RuO4 that we focus on.Chapter 2: In this chapter,relevant experiments that can show the symmetry of Sr2 RuO4pairing are introduced.In the first part,the experimental basis of the triplet pairing of the chiral pwave is introduced.The experiments of NMR,spin polarized neutron scattering and muon spin relaxation are introduced respectively.According to these experimental results,it is theoretically deduced that Sr2 RuO4 is a p+ip wave superconductor.In the second part,the experiments of specific heat,nuclear spin relaxation rate,thermal conductivity,ultrasonic attenuation and superfluid density physical properties are introduced.These experiments reveal that there are a large number of low-energy quasi particle excitation in the superconducting state of Sr2 RuO4,that is,there are nodes in the energy gap on the Fermi surface of Sr2 RuO4 superconductor,which is a typical feature of d-wave pairing.This is not consistent with the symmetry of the chiral p-wave,because the symmetry does not require that the p+ip wave pair has nodes.Chapter 3: In this chapter,the results of FRG calculation without considering and considering SOC are introduced.Regardless of SOC,Sr2 RuO4 is found to be chiral p-wave pairing and excited by a large number of low-energy quasiparticles,but the corresponding energy gap can not explain the linear specific heat and thermal conductivity measured at low temperature.Considering the SOC,it is found that although the pairing symmetry is a Chiral p wave,the atomic SOC induces a low energy quasi particle excitation similar to the node.Our theory explains why the chiral p-wave appears in the puzzle of d-wave behavior observed in thermal experiments.Chapter 4: In this chapter,the average field theory of superconductivity is briefly introduced,and then the specific heat,superfluid density,spin lattice relaxation rate,Knight shift and thermal conductivity thermodynamic properties of Sr2 RuO4 superconductor on the basis of FRG are calculated,and found that our results were in good agreement with the experimental results.Chapter 5: In this chapter,we study theoretically the quasiparticle interference(QPI)of Sr2 RuO4 in two possible superconducting states,chiral p-wave paired state and d-wave paired state,considering the SOC effect.which can provide an experimental method to identify the symmetry of Sr2 RuO4 pairing.The QPI spectra of these two pairing modes are different,so we can provide an experimental method to judge the pairing of Sr2 RuO4.Chapter 6: In this chapter,we summarize and review the whole paper. |
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