Influence of disorder on the signature of pseudogap and multigap superconducting behavior in FeSe

Abstract

We investigated several FeSe single crystals grown by two different methods by utilizing experimental techniques namely, resistivity, magnetoresistance, specific heat, scanning tunneling microscopy, and spectroscopy. The residual resistivity ratio (RRR) shows systematic differences between samples grown by chemical vapor transport and flux vapor transport, indicating variance in the amount of scattering centers. Although the superconducting transition temperature $T_c$ is not directly related to RRR, our study evidences subtle differences in the features of an incipient ordering mode related to a depletion of density of states at the Fermi level. For instance, the onset temperature of anisotropic spin-fluctuations at $T^{\ast }\approx 75$ K, and the temperature of the opening-up of a partial gap in the density of states at $T^{\ast \ast }\approx 30$ K are not discernible in the samples with lower RRR. Further, we show that the functional dependence of the electronic specific heat below 2 K, which allows to determine the nodal features as well as the small superconducting gap, differs significantly in crystals grown by these two different methods. Our investigation suggests that some of the controversies about the driving mechanism for the superconducting gap or its structure and symmetry is related to minute differences in the crystals arising due to the growth techniques used and the total amount of scattering centers present in the sample.

arXiv comment10 pages, 9 figures

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• On the Remarkable Superconductivity of FeSe and its Close Cousins
• Nodal gaps in the nematic superconductor FeSe from heat capacity
• Magnetic tricritical point and nematicity in FeSe under pressure
• Disorder-sensitive node-like small gap in FeSe
• Nematic state of the FeSe superconductor
• Suppression of Superconductivity and Nematic Order in Fe${}_{1-y}$Se${}_{1-x}$S${}_x$ (0$\le$$x$$\le$1, $y$$\le$0.1) Crystals by Anion Height Disorder
• Influence of electron irradiation on fluctuation conductivity and pseudogap in $YB{a}_{2}C{u}_3{O}_{7-\delta }$ single crystals
• Fluctuating Cooper pairs in FeSe at temperatures exceeding double Tc
• Specific Heat and the gap structure of a Nematic Superconductor, application to FeSe