Integer and half-integer flux-quantum transitions in a niobium/iron-pnictide loop

Abstract

The recent discovery of iron-based superconductors challenges the existing paradigm of high-temperature superconductivity. Owing to their unusual multi-orbital band structure, magnetism, and electron correlation, theories propose a unique sign reversed s-wave pairing state, with the order parameter changing sign between the electron and hole Fermi pockets. However, because of the complex Fermi surface topology and material related issues, the predicted sign reversal remains unconfirmed. Here we report a novel phase-sensitive technique for probing unconventional pairing symmetry in the polycrystalline iron-pnictides. Through the observation of both integer and half-integer flux-quantum transitions in composite niobium/iron-pnictide loops, we provide the first phase-sensitive evidence of the sign change of the order parameter in NdFeAsO0.88F0.12, lending strong support for microscopic models predicting unconventional s-wave pairing symmetry. These findings have important implications on the mechanism of pnictide superconductivity, and lay the groundwork for future studies of new physics arising from the exotic order in the FeAs-based superconductors.

23 pages, including 4 figures and supplementary information

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• Theory for Superconductivity in Iron Pnictides at Large Coulomb U Limit
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Cited by in corpus (80)

• The Puzzle of High Temperature Superconductivity in Layered Iron Pnictides and Chalcogenides
• Superconductivity in Iron Compounds
• High-temperature superconductivity in iron-based materials
• Gap symmetry and structure of Fe-based superconductors
• Iron-Based Superconductors: current status of materials and pairing mechanism
• Ironing out the details of unconventional superconductivity
• Unconventional Superconductivity
• Competing order and nature of the pairing state in the iron pnictides
• Functional Renormalization Group for multi-orbital Fermi Surface Instabilities
• Spectroscopic scanning tunneling microscopy insights into Fe-based superconductors
• Using Gap Symmetry and Structure to Reveal the Pairing Mechanism in Fe-based Superconductors
• Nodal superconducting gap structure in ferropnictide superconductor BaFe2(As0.7P0.3)2
• Unconventional Anisotropic s-Wave Superconducting Gaps of LiFeAs Iron-Pnictide Superconductor
• Manifestations of nematic degrees of freedom in the magnetic, elastic, and superconducting properties of the iron pnictides
• Resonant and crossover phenomena in a multiband superconductor tuning the chemical potential near a band edge
• Scanning Tunneling Microscopy/Spectroscopy of Vortices in LiFeAs
• Spin fluctuations in iron pnictides and chalcogenides: From antiferromagnetism to superconductivity
• Massless Leggett Mode in Three-band Superconductors with Time-Reversal-Symmetry Breaking
• Using controlled disorder to distinguish $s_{\pm }$ and $s_{++}$ gap structure in Fe-based superconductors
• First-principles calculation of transition-metal impurities in LaFeAsO
• Multigap superconductivity and strong electron-boson coupling in Fe-based superconductors: A point-contact Andreev-reflection study of Ba(Fe1-xCox)2As2 single crystals
• Reciprocal-space structure and dispersion of the magnetic resonant mode in the superconducting phase of Rb(x)Fe(2-y)Se2 single crystals
• Superconducting Properties of the $s^{\pm }$-wave state: Fe-based superconductors
• Observation of Half-Quantum Flux in Unconventional Superconductor $\beta$-Bi${}_2$Pd
• Thin Film Growth and Device Fabrication of Iron-Based Superconductors
• Measurement of a Sign-Changing Two-Gap Superconducting Phase in Electron-Doped Ba(Fe_{1-x}Co_x)_2As_2 Single Crystals using Scanning Tunneling Spectroscopy
• Shape resonance for the anisotropic superconducting gaps near a Lifshitz transition: the effect of electron hopping between layers
• Linear decrease of critical temperature with increasing Zn substitution in the iron-based superconductor BaFe1.89-2xZn2xCo0.11As2
• DC superconducting quantum interference devices fabricated using bicrystal grain boundary junctions in Co-doped BaFe2As2 epitaxial films
• BaFe_{1.8}Co_{0.2}As_2 thin film hybrid Josephson junctions
• Sign inversion in the superconducting order parameter of LiFeAs inferred from Bogoliubov quasiparticle interference
• Josephson effect between a two-band superconductor with the s++ or s+- pairing symmetry and a conventional s-wave superconductor
• Identical effects of indirect and direct electron doping of superconducting BaFe2As2 thin films
• Evidence for a cos(4φ) Modulation of the Superconducting Energy Gap of Optimally Doped FeTe_{0.6}Se_{0.4} Single Crystals Using Laser Angle-Resolved Photoemission Spectroscopy
• Ground state, collective mode, phase soliton and vortex in multiband superconductors
• Single Impurity Problem in Iron-Pnictide Superconductors
• Effect of a Zn impurity on T_c and its implication to pairing symmetry in LaFeAsO${}_{1-x}$F${}_x$
• Transfer of optical spectral weight in magnetically ordered superconductors
• Designing phase-sensitive tests for Fe-based superconductors
• Entangled Orbital Triplet Pairs in Iron-Based Superconductors
• Ambegaokar-Baratoff relations of Josephson critical current in heterojunctions with multi-gap superconductors
• Odd parity pairing and nodeless anti-phase $s^{\pm }$ in Iron-Based Superconductors
• Proximity and Josephson effects in microstructures based on multiband superconductors
• Phase soliton and pairing symmetry of a two-band superconductor: Role of the proximity effect
• Magnetic excitations in underdoped Ba(Fe1-xCox)2As2 with x=0.047
• Quasiparticle interference in an iron-based superconductor
• Phase-sensitive evidence for the sign-reversal s+- symmetry of the order parameter in an iron-pnictide superconductor using Nb/Ba1-xNaxFe2As2 Josephson junctions
• Microwave Surface Impedance Measurements of the Electronic State and Dissipation of Magnetic Vortices in Superconducting Iron-Based LiFeAs Single Crystals
• Superconducting phase fluctuations in SmFeAsO${}_{0.8}$F${}_{0.2}$ from diamagnetism at low magnetic field above $T_c$
• Metastable $\pi$-junction between an s${}_{\pm }$-wave and an s-wave superconductor
• Shapiro Steps as a Direct Probe of $\pm s$-wave Symmetry in Multi-gap Superconducting Josephson Junctions
• Effect of electron-phonon interactions on orbital fluctuations in iron-based superconductors
• Observation of Multi-Gap Superconductivity in GdO(F)FeAs by Andreev Spectroscopy
• Zn-impurity effect and interplay of $s_{\pm }$- and $s_{++}$-pairings in Fe-based superconductors
• Josephson currents in point contacts between dirty two-band superconductors
• Effects of isoelectronic Ru substitution at the Fe site on the energy gaps of optimally F-doped SmFeAsO
• Proximity fingerprint of s+- superconductivity
• Anomalous Josephson Coupling and High-Harmonics in Non-Centrosymmetric Superconductors with $S$-wave Spin-Triplet Pairing
• Influence of the Fermi surface geometry on a Josephson effect between an iron-pnictide and conventional superconductors
• Consistent picture for the electronic structure around a vortex core in iron-based superconductors
• Josephson current and density of states in proximity circuits with s+- superconductors
• Determination of the pairing state in iron-based superconductors through neutron scattering
• Probing the Order Parameter of Superconducting LiFeAs using Pb/LiFeAs and Au/LiFeAs Point-Contact Spectroscopy
• Evolution of the Fermi surface topology in doped 122 iron pnictides
• Magnetoresistance oscillation study of the half-quantum vortex in doubly connected mesoscopic superconducting cylinders of Sr2RuO4
• Possible pi-phase shift at interface of two pnictides with antiphase s-wave pairing
• Fractional Flux Plateau in Magnetization Curve of Multicomponent Superconductor Loop
• Magnetic orders, excitations, and phase transitions in Fe_1+yTe
• Theoretical approach to resonant inelastic x-ray scattering in iron-based superconductors at the energy scale of the superconducting gap
• Q-scan-analysis of the neutron scattering in iron-based superconductors
• Strain-induced superconductivity in Sr2IrO4
• Suppression of $T_c$ by Zn impurity in the electron-type LaFe${}_{0.925-y}$Co${}_{0.075}$Zn${}_y$AsO system
• Evolution of quasiparticle states with and without a Zn-impurity in doped 122 iron pnictides
• Signatures of unconventional pairing in near-vortex electronic structure of LiFeAs
• Study of Ni and Zn doped CeOFeAs: Effect on the structural transition and specific heat capacity
• Precision determination of a fluxoid quantum's magnetic moment in a superconducting micro-ring
• Conductance spectrum and superconducting gap structures observed in c-axis FeSe0.3Te0.7/Au junctions
• Effects of order parameter self-consistency in a $s_{\pm }$-s junction
• Shot Noise as a probe for the pairing symmetry of Iron pnictide superconductors
• Single-band to two-band superconductivity transition in two-dimensional oxide interfaces