The quasiparticles in the normal state of iron-based superconductors have been shown to behave universally as a 3-dimensional Fermi liquid. Because of interactions and the presence of sharp Fermi surfaces, the quasiparticle energy contains, as a function of the momentum $$\varvec{p}$$
 , a term of the form $$( p - p_0)^3 \ln {( |p-p_0|/p_0)} $$
 , where $$p = | \varvec{p} |$$
 and $$p_0$$
 is the Fermi momentum. The electronic specific heat coefficient, magnetic susceptibility (Knight shift), electrical resistivity, Hall coefficient and thermoelectric power divided by temperature follow, as functions of temperature T, the logarithmic formula $$a-b T^2 \ln {(T/T^*)}$$
 , $$a, \, b$$
 and $$T^*$$
 being constant; these formulae have been shown to explain the observed data for all iron-based superconductors. It is shown that the concept of non-Fermi liquids or anomalous metals which appears in the literature is not needed for descriptions of the present systems. When the superconducting transition temperature $$T_{\mathrm {C}}$$
 and the b / a value for the resistivity are plotted as functions of the doping content x, there appear various characteristic diagrams in which regions of positive correlation and those of negative correlation between $$T_{\mathrm {C}}$$
 and b / a are interconnected; from these diagrams, we may make speculations about the types of superconductivity and the crossover between them.

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The 3-Dimensional Fermi Liquid Description for the Iron-Based Superconductors

Heavy fermion like behavior in layered Ce-based oxysulfides

One of difficult problems in iron-based superconductors (normal state) is that the temperature (T) variation of the electrical resistivity deviates from the T2 law. Here we resolve this problem by assuming that the systems are truly 3-dimensional (3D) Fermi liquids. Because of interactions and the presence of Fermi surface, the quasiparticle energy measured from the Fermi surface, e, contains, as a function of momentum p with the Fermi momentum p0, a (p − p0)3 ln|p − p0| term which produces a e2 ln|e| term in the density-of-states function. This term gives rise to a T2 ln T term in the electronic specific heat coefficient, impurity resistivity and total resistivity. Spin-antisymmetric short-wavelength density fluctuations creates a T2 ln T variation of the magnetic susceptibility. We show that existing experimental data obey universally this T2 ln T law. Through this analysis we find a close correlation between the magnitude of the e2 ln|e| term and superconducting transition temperatures; this suggests t...

A Close Correlation between the Logarithmic Quasiparticle Energy and Superconducting Transition Temperatures of Iron-Pnictide Compounds

It is generally believed that behaviours of quasiparticles (holes) in high-$T_{\rm C}$ cupurates should be attributed to the two-dimensional (2D) electronic states in the CuO$_{2}$ planes. The various anomalies of the transport coefficients for temperatures above $T_{\rm C}$ are long-standing insoluble puzzles and cause serious controversy. Here we reanalyse the published experimental date of LSCO cupurates. We find that the normal-state susceptibility, resistivity, Hall coefficient etc vary precisely as $T^{2}\ln T$ as a function of temperature $T$ in agreement with the prediction of the Fermi liquid model. The quasiparticles are shown to definitely behave as a 3D Fermi liquid. Various attempts to describe the system in terms of non-Fermi liquids,e.g. the RVB state, seem to be erroneous.

Setsuo Misawa

Papers

Strong evidence for the three-dimensional Fermi liquid behaviour of quasiparticles in high-$T_{\rm C}$ cupurates