Spectroscopic scanning tunneling microscopy insights into Fe-based superconductors

Abstract

In the first three years since the discovery of Fe-based high Tc superconductors, scanning tunneling microscopy (STM) and spectroscopy have shed light on three important questions. First, STM has demonstrated the complexity of the pairing symmetry in Fe-based materials. Phase-sensitive quasiparticle interference (QPI) imaging and low temperature spectroscopy have shown that the pairing order parameter varies from nodal to nodeless s\pm within a single family, FeTe1-xSex. Second, STM has imaged C4 -> C2 symmetry breaking in the electronic states of both parent and superconducting materials. As a local probe, STM is in a strong position to understand the interactions between these broken symmetry states and superconductivity. Finally, STM has been used to image the vortex state, giving insights into the technical problem of vortex pinning, and the fundamental problem of the competing states introduced when superconductivity is locally quenched by a magnetic field. Here we give a pedagogical introduction to STM and QPI imaging, discuss the specific challenges associated with extracting bulk properties from the study of surfaces, and report on progress made in understanding Fe-based superconductors using STM techniques.

36 pages, 23 figures, 229 references

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• Superconductivity at 43 K in Samarium-arsenide Oxides $SmFeAs{O}_{1-x}{F}_x$
• Unconventional pairing originating from disconnected Fermi surfaces in superconducting LaFeAsO${}_{1-x}$F${}_x$}
• LaFeAsO${}_{1-x}$F${}_x$: A low carrier density superconductor near itinerant magnetism
• Superconductivity at 41 K and its competition with spin-density-wave instability in layered CeO${}_{1-x}$F${}_x$FeAs
• Superconductivity at 22 K in Co-doped BaFe2As2 Crystals
• Topological Surface States Protected From Backscattering by Chiral Spin Texture
• Scanning tunneling spectroscopy of high-temperature superconductors
• Observation of Fermi-surface-dependent nodeless superconducting gaps in Ba0.6K0.4Fe2As2
• Evidence for an electron nematic phase transition in underdoped iron pnictide superconductors
• Magnetic order in BaFe2As2, the parent compound of the FeAs based superconductors in a new structural family
• Theory of Electron Nematic Order in LaOFeAs
• Superconductivity in iron-based F-doped layered quaternary compound Nd[O1-xFx]FeAs
• Thorium-doping induced superconductivity up to 56 K in Gd1-xThxFeAsO
• Very High Field Two-Band Superconductivity in LaFeAsO_0.89F_0.11
• First-order magnetic and structural phase transitions in Fe${}_{1+y}$Se${}_x$Te${}_{1-x}$
• The Structural Phase Transition in FeSe (Fe1+dSe)
• Superconductivity up to 29 K in SrFe2As2 and BaFe2As2 at high pressures
• Ising and Spin orders in Iron-based Superconductors
• Superconductivity at 52 K in iron-based F-doped layered quaternary compound Pr[O1-xFx]FeAs
• Fe-based high temperature superconductivity with Tc=31K bordering an insulating antiferromagnet in (Tl,K)FexSe2 Crystals
• The electronic phase diagram of the LaO1-xFxFeAs superconductor
• Anisotropic thermodynamic and transport properties of single crystalline (Ba${}_{1-x}$K${}_x$)Fe${}_2$As${}_2$ (x = 0 and 0.45)
• Two Gaps Make a High Temperature Superconductor?
• Small anisotropy, weak thermal fluctuations, and high field superconductivity in Co-doped iron pnictide Ba(Fe1-xCox)2As2
• Spin-orbital frustrations and anomalous metallic state in iron-pnictide superconductors
• Lattice and magnetic instabilities in CaFe2As2: A single crystal neutron diffraction study
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• Superconductivity induced by Ni doping in BaFe${}_2$As${}_2$
• Origin of the spin density wave instability in AFe${}_2$As${}_2$ (A=Ba, Sr) as revealed by optical spectroscopy
• ${}^{75}$As NMR studies of superconducting LaO${}_{0.9}$F${}_{0.1}$FeAs
• Scanning Tunneling Spectroscopy and Vortex Imaging in the Iron-Pnictide Superconductor BaFe${}_{1.8}$Co${}_{0.2}$As${}_2$
• Superconductivity at 17 K in (Fe2P2)(Sr4Sc2O6): a new superconducting layered pnictide oxide with a thick perovskite oxide layer
• Orbital Order and Spontaneous Orthorhombicity in Iron Pnictides
• Evidence for nodal superconductivity in LaFePO
• Mechanics of Individual, Isolated Vortices in a Cuprate Superconductor
• Field and Temperature Dependence of the Superfluid Density in LaO_{1-x}F_xFeAs Superconductors: A Muon Spin Relaxation Study
• Critical Fields and Anisotropy of NdO0.82F0.18FeAs Single Crystals
• Evolution of the electronic excitation spectrum with strongly diminishing hole-density in superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}
• Unconventional London penetration depth in Ba(Fe0.93Co0.07)2As2 single crystals
• Momentum-dependence of Superconducting Gap, strong-coupling dispersion Kink, and tightly bound Cooper pairs in the high-Tc (Sr,Ba)1-x(K,Na)xFe2As2 superconductors
• Observation of Lattice and Andreev Bound States of Vortices in Ba0.6K0.4Fe2As2 Single Crystals with Scanning Tunneling Microscopy/Spectroscopy
• Antiferromagnetically Driven Electronic Correlation in Iron Pnictides and Cuprates
• 19-F NMR Investigation of Iron-pnictide Superconductor LaFeAsO(0.89)F(0.11)
• Extending Universal Nodal Excitations Optimizes Superconductivity in Bi2Sr2CaCu2O8+d
• Point-Contact Spectroscopy of Iron-Based Layered Superconductor LaO${}_{0.9}$F${}_{0.1-\delta }$FeAs
• Doping evoluton of antiferromagnetic order and structural distortion in LaFeAsO${}_{1-x}$F${}_x$
• Coexistence of competing orders with two energy gaps in real and momentum space in high-Tc superconductor Bi2Sr2-xLaxCuO6+delta
• High pressure synthesis of late rare earth RFeAs(O,F) superconductors; R = Tb and Dy
• Evidence for Unconventional Superconductivity in Arsenic-Free Iron-Based Superconductor FeSe : A ^77Se-NMR Study
• The cleavage surface of the BaFe_(2-x)Co_(x)As_(2) and Fe_(y)Se_(1-x)Te_(x) superconductors: from diversity to simplicity
• First Homologous Series of Iron Pnictide Oxide Superconductors (Fe2As2)(Can+1(Sc,Ti)nOy) [n = 3,4,5] with Extremely Thick Blocking Layers
• Fourier transform spectroscopy of d-wave quasiparticles in the presence of atomic scale pairing disorder
• Nanoscale superconducting gap variations, strong coupling signatures and lack of phase separation in optimally doped BaFe1.86Co0.14As2
• Scanning tunneling spectroscopy of SmFeAsO0.85: Possible evidence for d-wave order parameter symmetry
• Different response of the crystal structure to isoelectronic doping in BaFe2[As(1-x)P(x)]2 and [Ba(1-x)Sr(x)]Fe2As2
• ARPES studies of the electronic structure of LaOFe(P,As)
• Antiferromagnetic Correlation and the Pairing Mechanism of the Cuprates and Iron Pnictides : a View From the Functional Renormalization Group Studies
• Existence, character and origin of surface-related bands in the high temperature iron pnictide superconductor BaFe_{2-x}Co_{x}As_{2}
• 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
• New Iron Arsenide Oxides (Fe2As2)(Sr4(Sc,Ti)3O8), (Fe2As2)(Ba4Sc3O7.5), and (Fe2As2)(Ba3Sc2O5)
• Model for nodal quasiparticle scattering in a disordered vortex lattice
• A high resolution, hard X-ray photoemission investigation of BaFe${}_2$As${}_2$: moderate influence of the surface and evidence for a low degree of Fe 3d - As 4p hybridization of the near-E${}_F$ electronic states
• Spectroscopic Imaging Scanning Tunneling Microscopy as a Probe of Orbital Structures and Ordering
• Limits on the Superconducting Order Parameter in NdFeAsO${}_{1-x}$F${}_y$ from Scanning SQUID Microscopy
• Vortex state in iron-based superconductors with collinear antiferromagnetic cores
• Pseudogap-less high T${}_c$ superconductivity in BaCo${}_x$Fe${}_{2-x}$As${}_2$
• Metastable $\pi$-junction between an s${}_{\pm }$-wave and an s-wave superconductor
• Reaffirming the $d_{x^2-y^2}$ superconducting gap using the auto-correlation angle-resolved photoemission spectroscopy of Bi${}_{1.5}$Pb${}_{0.55}$Sr${}_{1.6}$La${}_{0.4}$CuO${}_{6+\delta }$
• Quasiparticle interference in antiferromagnetic parent compounds of Fe-based superconductors

Cited by in corpus (112)

• Iron-Based Superconductors: current status of materials and pairing mechanism
• Majorana corner modes in a high-temperature platform
• Unconventional Superconductivity
• Role of the orbital degree of freedom in iron-based superconductors
• Two superconducting components with different symmetries in Nd1-xSrxNiO2 films
• A review of two-band superconductivity: materials and effects on the thermodynamic and reversible mixed-state properties
• Probing topological quantum matter with scanning tunnelling microscopy
• Imaging superconducting vortex core and lattice with the scanning tunneling microscope
• Evidence of topological Shiba bands in artificial spin chains on superconductors
• Suppression of Superconductivity by Twin Boundaries in FeSe
• Scrutinizing the double superconducting gaps and strong coupling pairing in (Li1-xFexOH)FeSe
• Interpretation of scanning tunneling quasiparticle interference and impurity states in cuprates
• Scanning tunneling spectroscopy of superconducting LiFeAs single crystals: Evidence for two nodeless energy gaps and coupling to a bosonic mode
• Effect of vortex hotspots on the radio-frequency surface resistance of superconductors
• No observation of chiral flux current in the topological kagome metal CsV${}_3$Sb${}_5$
• Superconductivity in nickel based 112 systems
• Superconducting Properties of the $s^{\pm }$-wave state: Fe-based superconductors
• Interface high-temperature superconductivity
• Nodeless multiband superconductivity in stoichiometric single crystalline CaKFe${}_4$As${}_4$
• Influence of the multiband sign changing superconductivity on the vortex cores and on vortex pinning in the new stoichiometric high Tc CaKFe4As4
• Evidence of a spin resonance mode in the iron-based superconductor Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$ from scanning tunneling spectroscopy
• Visualizing the microscopic coexistence of spin density wave and superconductivity in underdoped NaFe1-xCoxAs
• Multi-Band Exotic Superconductivity in the New Superconductor Bi4O4S3
• Strong coupling superconductivity and prominent superconducting fluctuations in the new superconductor Bi4O4S3
• Topological Ultranodal pair states in iron-based superconductors
• Bound States of Defects in Superconducting LiFeAs Studied by Scanning Tunneling Spectroscopy
• Local inhomogeneity and filamentary superconductivity in Pr-doped CaFe${}_2$As${}_2$
• In-Gap Quasiparticle Excitations Induced by Non-Magnetic Cu Impurities in Na(Fe0.96Co0.03Cu0.01)As Revealed by Scanning Tunneling Spectroscopy
• Checkerboard stripe electronic state on cleaved surface of NdO${}_{0.7}$F${}_{0.3}$BiS${}_2$ probed by scanning tunneling microscope
• Emergence of an incipient ordering mode in FeSe
• Unconventional disorder effects in correlated superconductors
• Impurity states and cooperative magnetic order in Fe-based superconductors
• Evolution from unconventional spin density wave to superconductivity and a novel gap-like phase in NaFe1-xCoxAs
• Dopant Clustering, Electronic Inhomogeneity, and Vortex Pinning in Iron-Based Superconductors
• Entangled Orbital Triplet Pairs in Iron-Based Superconductors
• Zero-bias conductance peak in detached flakes of superconducting 2H-TaS${}_2$ probed by scanning tunneling spectroscopy
• Strong-Coupling Superconductivity in NaFe${}_{1-x}$Co${}_x$As: the Eliashberg Theory and Beyond
• Determination of the trigonal warping orientation in Bernal-stacked bilayer graphene via scanning tunneling microscopy
• Nanoscale Surface Element Identification and Dopant Homogeneity in the High-$T_c$ Superconductor Pr${}_x$Ca${}_{1-x}$Fe${}_2$As${}_2$
• Influence of $s_{\pm }$ symmetry on unconventional superconductivity in pnictides above the Pauli limit -- two-band model study
• Two distinct superconducting states controlled by orientation of local wrinkles in LiFeAs
• Unexpected weak spatial variation of local density of sates induced by individual Co impurity atoms in Na(Fe{1-x}Cox)As as revealed by scanning tunneling spectroscopy
• Surface terminations and layer-resolved spectroscopy in 122 iron pnictide superconductors
• Single particle tunneling spectroscopy and superconducting gaps in layered iron based superconductor KCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Tilted vortex cores and superconducting gap anisotropy in 2H-NbSe2
• Deep data mining in a real space: Separation of intertwined electronic responses in a lightly-doped BaFe2As2
• Fully gapped superconductivity in In-doped topological crystalline insulator Pb${}_{0.5}$Sn${}_{0.5}$Te
• Vector field controlled vortex lattice symmetry in LiFeAs
• Direct visualization of sign reversal s^+- superconducting gaps in FeTe0.55Se0.45
• Simplified feedback control system for Scanning Tunneling Microscopy
• Improving quantum-transition temperatures in BaFe2As2-based crystals by removing local-lattice strain & electronic-structure disorder
• Pairing insights in iron-based superconductors from scanning tunneling microscopy
• Strong coupling superconductivity revealed by scanning tunneling microscope in tetragonal FeS
• Direct visualization of phase separation between superconducting and nematic domains in Co-doped CaFe2As2 close to a first order phase transition
• Real-space BCS-BEC crossover in FeSe monolayer
• Tunneling spectroscopy for probing orbital anisotropy in iron pnictides
• Progress in nonmagnetic impurity doping studies on Fe-based superconductors
• Electronic vortex structure of Fe-based superconductors: application to LiFeAs
• Experimental observation of an anomalous peak in isofield M(T) curves in BaFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$ resembling the fish-tail in $M$($H$) curves further suggesting a possible phase transition in the irreversible regime
• Twofold symmetry of proximity-induced superconductivity in Bi${}_2$Te${}_3$/Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta }$ heterostructures revealed by scanning tunneling microscopy
• Sign reversal superconducting gaps revealed by phase referenced quasi-particle interference of impurity induced bound states in (Li${}_{1-x}$Fe${}_x$)OHFe${}_{1-y}$Zn${}_y$Se
• Experimental investigation of the electronic structure of Ca${}_{0.83}$La${}_{0.17}$Fe${}_2$As${}_2$
• Effect of surface morphology and magnetic impurities on the electronic structure in cobalt-doped BaFe2As2 superconductors
• TAO pairing: a fully gapped pairing scenario for the Iron-Based Superconductors
• The superconducting gaps in FeSe studied by soft point-contact Andreev reflection spectroscopy
• Orbital selectivity of layer resolved tunneling on iron superconductor Ba0.6K0.4Fe2As2
• Reshaped Weyl fermionic dispersions driven by Coulomb interactions in MoTe2
• Local characterization of a heavy-fermion superconductor via sub-Kelvin magnetic force microscopy
• Phase-sensitive determination of nodal $\mathbf{d}$-wave order parameter in single-band and multiband superconductors
• Low work function in the 122-family of iron-based superconductors
• Impurity bound states and disorder-induced orbital and magnetic order in the s+- state of Fe-based superconductors
• Observation of Coulomb blockade and Coulomb staircases in superconducting Pr0.8Sr0.2NiO2 films
• Multiband superconductivity and possible nodal gap in RbCr${}_3$As${}_3$ revealed by Andreev reflection and single-particle tunneling measurements
• Quasi-one Dimensional Nanostructures as Sign of Nematicity in Iron Pnictides and Chalcogenides
• Enhanced spin ordering temperature in ultrathin FeTe films grown on a topological insulator
• Local Superconductivity in Vanadium Iron Arsenide
• Quasiparticle interference of heavy fermions in resonant X-ray scattering
• Theoretical study on the anisotropic electronic structure of antiferromagnetic BaFe${}_2$As${}_2$ and Co-doped Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$ seen by angle-resolved photoemission
• Vortex lattice and vortex bound states in CsFe${}_2$As${}_2$ investigated by scanning tunneling microscopy/spectroscopy
• An STM perspective on hexaborides: Surface states of the Kondo insulator SmB${}_6$
• Superconducting gap symmetry from Bogoliubov quasiparticle interference analysis on {Sr}${}_2${RuO}${}_4$
• Surface adatom conductance filtering in scanning tunneling spectroscopy of Co-doped BaFe2As2 iron pnictide superconductors
• Fermionology in the Kondo-Heisenberg model: the case of CeCoIn${}_5$
• Inhomogeneous superconductivity onset in FeSe studied by transport properties
• Absence of hexagonal to square structural transition in LiFeAs vortex matter
• Weyl semimetallic state with antiferromagnetic order in Rashba-Hubbard model
• Surface reconstruction and charge modulation in BaFe2As2 superconducting film
• Isotropic multi-gap superconductivity in BaFe1.9Pt0.1As2 from thermal transport and spectroscopic measurements
• Observation of a Smoothly Tunable Dirac Point in $Ge(B{i}_{x}S{b}_{1-x}{)}_{2}T{e}_4$
• Superconductivity with Tc=7 K under pressure for Cu-, and Au-doped BaFe2As2
• Local spin-density-wave order inside vortex cores in multiband superconductors
• Necklace-like pattern of vortex bound states
• Compressed Sensing for STM imaging of defects and disorder
• Atomic-scale analysis of disorder by similarity learning from tunneling spectroscopy
• Superconductivity and vortex structure on Bi${}_2$Te${}_3$/FeTe${}_{0.55}$Se${}_{0.45}$ heterostructures with different thickness of Bi${}_2$Te${}_3$ films
• Atomic Visualization of Bulk and Surface Superconductivity in Weyl Semimetal γ-PtBi2
• Tuning the magnetism of the top-layer FeAs on BaFe${}_2$As${}_2$(001): First-principles study
• Investigation of magnetic phases in parent compounds of Iron-chalcogenides via quasiparticle scattering interference
• Scanning Tunneling Spectroscopy on SrFe${}_2$(As${}_{1-\mathrm{x}}$P${}_{\mathrm{x}}$)${}_2$
• Anisotropic superconductivity and Fermi surface reconstruction in the spin-vortex antiferromagnetic superconductor CaK(Fe${}_{0.95}$Ni${}_{0.05}$)${}_4$As${}_4$
• Effects of order parameter self-consistency in a $s_{\pm }$-s junction
• Weakening of the spin density wave gap at low temperatures in SrFe${}_2$As${}_2$ single crystals
• Impact of atomic defects in the electronic states of FeSe${}_{1-x}$S${}_x$ superconducting crystals
• Electronic inhomogeneities in the superconducting phase of CaFe1.96Ni0.04As2 single crystals
• Magnetic-field driven evolution of zero-energy mode on Bi islands deposited on Fe(Te,Se)
• Thermodynamics of $s_{\pm }-to-s_{++}$ transition in iron pnictides in the vicinity of the Born limit
• Image of helical local moment magnetic order in the STM spectrum
• Observation of Two Cascading Screening Processes in an Iron-based Superconductor
• Analyzing scanning tunneling spectroscopy for Fe-based superconductor Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ and extracting $s$-wave density of states
• Quasiparticle interference in LiFeAs: Signature of inelastic tunneling through spin fluctuations
• Proximity-Induced Superconductivity in a Topological Crystalline Insulator
• Absence of coherent peaks in a $Z_2$ fractionalized BCS superconducting state