Opening of a pseudogap in a quasi-two-dimensional superconductor due to critical thermal fluctuations

Abstract

We examine the role of the anisotropy of superconducting critical thermal fluctuations in the opening of a pseudogap in a quasi-two-dimensional superconductor such as a cuprate-oxide high-temperature superconductor. When the anisotropy between planes and their perpendicular axis is large enough and its superconducting critical temperature Tc is high enough, the fluctuations are much developed in the critical region so that lifetime widths of quasiparticles are large and the energy dependence of the self-energy deviates from that of Landau’s normal Fermi liquids. A pseudogap opens in such a critical region because quasiparticle spectra around the chemical potential are swept away due to the large lifetime widths. The pseudogap never smoothly evolves into a superconducting gap; it starts to open at a temperature higher than Tc while the superconducting gap starts to open just at Tc. When Tc is rather low but the ratio of εG(0)∕kBTc, with εG(0) the superconducting gap at T=0K, is much larger than a value of about 4 according to the mean-field theory, the pseudogap must be closing as temperature T approaches to the low Tc because thermal fluctuations become less developed as T decreases. Critical thermal fluctuations cannot cause the opening of a prominent pseudogap in an almost isotropic three-dimensional superconductor, even if its Tc is high.

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