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

TL;DR

This study examines how different crystal growth methods affect the electronic properties and superconducting features of FeSe, revealing that subtle differences in disorder influence the pseudogap and multigap behavior.

Contribution

It demonstrates that growth-induced disorder impacts the pseudogap signatures and superconducting gap structure in FeSe, clarifying discrepancies in previous studies.

Findings

Differences in RRR correlate with variations in spin-fluctuation onset and partial gap opening.

Superconducting gap features vary significantly with growth method.

Disorder influences the interpretation of superconducting mechanisms 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 $T^* \approx 75$ K, and the temperature of the opening-up of a partial gap in the density of states at $T^{**} \approx 30$ 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.