Preformed Cooper pairs in layered FeSe-based superconductors

Abstract

Superconductivity arises from two distinct quantum phenomena: electron pairing and long-range phase coherence. In conventional superconductors, the two quantum phenomena generally take place simultaneously, while the electron pairing occurs at higher temperature than the long-range phase coherence in the underdoped high-Tc cuprate superconductors. Recently, whether electron pairing is also prior to long-range phase coherence in single-layer FeSe film on SrTiO3 substrate is under debate. Here, by measuring Knight shift and nuclear spin-lattice relaxation rate, we unambiguously reveal a pseudogap behavior below Tp ~ 60 K in two layered FeSe-based superconductors with quasi-two-dimension. In the pseudogap regime, a weak diamagnetic signal and a remarkable Nernst effect are also observed, which indicate that the observed pseudogap behavior is related to superconducting fluctuations. These works confirm that strong phase fluctuation is an important character in the two-dimensional iron-based superconductors as widely observed in high-Tc cuprate superconductors.

18 pages, 4 figures, supplementary materials available upon request

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• Revealing the Empty-State Electronic Structure of Single-Unit-Cell FeSe/SrTiO${}_3$
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• Dipolar phonons and electronic screening in monolayer FeSe on SrTiO${}_3$
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• Nernst effect of the new iron-based superconductor LaO${}_{1-x}$F${}_x$FeAs
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Cited by in corpus (29)

• When Superconductivity Crosses Over: From BCS to BEC
• Incoherent Cooper pairing and pseudogap behavior in single-layer FeSe/SrTiO${}_3$
• Spectroscopic Evidence of Superconductivity Pairing at 83 K in Single-Layer FeSe/SrTiO3 Films
• Mott-driven BEC-BCS crossover in a doped spin liquid candidate, kappa-(BEDT-TTF)4Hg2.89Br8
• Phase coherence of pairs of Cooper pairs as quasi-long-range order of half-vortex pairs in a two-dimensional bilayer system
• Interfacial Electron-Phonon Coupling Constants Extracted from Intrinsic Replica Bands in Monolayer FeSe/SrTiO${}_3$
• Evolution of transport properties in FeSe thin flakes with thickness approaching the two-dimensional limit
• Quasi two-dimensional nature of high-Tc superconductivity in iron-based (Li,Fe)OHFeSe
• Mechanism of screening or enhancing the pseudogap throughout the two-band Bardeen-Cooper-Schrieffer to Bose-Einstein condensate crossover
• Lattice fluctuations, not excitonic correlations, mediated electronic localization in TiSe${}_2$
• Positive and negative chemical pressure effects investigated in electron-doped FeSe films with an electric-double-layer structure
• Density-Induced Hadron-Quark Crossover via the Formation of Cooper Triples
• Test for BCS-BEC Crossover in the Cuprate Superconductors
• Ubiquitous light real-space pairing from long-range hopping and interactions
• Superconducting fluctuations and charge-4$e$ plaquette state at strong coupling
• Unusual band splitting and superconducting gap evolution with sulfur substitution in FeSe
• Unraveling spin texture and spin-orbit coupling contributions in spin triplet superconductivity
• Interplay of electron-phonon coupling, pseudogap, and superconductivity in CsCa${}_2$Fe${}_4$As${}_4$F${}_2$ studied using ultrafast optical spectroscopy
• Spin correlations in the parent phase of Li${}_{1-x}$Fe${}_x$ODFeSe
• Study on fluctuations of interface-enhanced superconductivity in ultrathin FeSe/SrTiO3 by the Nernst effect
• Preformed Cooper Pairs in a Triclinic Iron Pnictide Superconductor
• Hidden Pseudogap and Excitation Spectra in a Strongly Coupled Two-Band Superfluid/Superconductor
• Inferior interfacial superconductivity in 1 UC FeSe/SrVO${}_3$/SrTiO${}_3$ with screened interfacial electron-phonon coupling
• Nodeless multigap superconductivity in organic-ion-intercalated (tetrabutyl~ammonium)${}_{0.3}$FeSe
• Unique quantum metallic state in the titanium sesquioxide heterointerface superconductor
• Real-space d-wave superconductivity from weak attraction
• Fragile pressure-induced magnetism in FeSe superconductors with a thickness reduction
• What controls the superconducting dome of electron-doped FeSe?
• Enhancement of Superconductivity Linked with Linear-in-Temperature/Field Resistivity in Ion-Gated FeSe Films