Unusual temperature evolution of superconductivity in LiFeAs

Abstract

We have performed temperature dependent tunneling spectroscopy on an impurity-free surface area of a LiFeAs single crystal. Our data reveal a highly unusual temperature evolution of superconductivity: at $T_c^{\ast }=18$~K a partial superconducting gap opens, as is evidenced by subtle, yet clear features in the tunneling spectra, i.e. particle-hole symmetric coherence peaks, and a dip-hump structure which signals strong-coupling superconductivity. At $T_c=16$~K, these features substantiate dramatically and become characteristic of full superconductivity. Remarkably, this is accompanied by an almost jump-like increase of the gap energy at $T_c$ to about 87\% of its low-temperature gap value. The energy of the bosonic mode as measured by the distance between the coherence peak and the higher-energy dip remains practically constant in the whole temperature regime $T\le T_c^{\ast }$. The comparison of these findings with established experimental and theoretical results lead us to suggest that the bosonic mode is not directly related to incommensurate spin fluctuations that have previously been observed in inelastic neutron scattering.

6 pages, 4 figures

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Cited by in corpus (10)

• Correlation-enhanced odd-parity inter-orbital singlet pairing in the iron-pnictide superconductor LiFeAs
• Effect of gap anisotropy on the spin resonance peak in the superconducting state of iron-based materials
• Tracing the electronic pairing glue in unconventional superconductors via inelastic Scanning Tunneling Spectroscopy
• Electron and Superconducting Properties of the AFeAs (A= Li, Na) Family Alkali-Metal Pnictides: Current Stage of the Research (mini-review)
• An ultra-high vacuum scanning tunneling microscope operating at sub-Kelvin temperatures and high magnetic fields for spin-resolved measurements
• Cooper pairs without 'glue' in high-$T_c$ superconductors
• Spectroscopic evidence of nematic fluctuations in LiFeAs
• Absence of hexagonal to square structural transition in LiFeAs vortex matter
• Local transformation of the Electronic Structure and Generation of Free Carriers in Cuprates and Ferropnictides under Heterovalent and Isovalent Doping
• Absence of nematic instability in LiFeAs