Detecting sign-changing superconducting gap in LiFeAs using quasiparticle interference

Altenfeld, D.; Hirschfeld, P. J.; Mazin, I. I.; Eremin, I.

doi:10.1103/physrevb.97.054519

Cited by 15 publications

(16 citation statements)

References 49 publications

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“…Indeed, in contrast to the zero-field picture of a sharp crossover, the lattice and liquids of moat-core vortices represent a lattice or a "mircoemulsion" of s ± inclusions inside the s ++ state. Moreover, as the vortex density raises in increasing field, there is also a field-induced crossover from s ++ to the s ± , which can be resolved in local phase-sensitive probes [22][23][24]. We also pointed out that in these systems in an applied external field, the superconducting state near the Meissner current carrying boundary can be s ± while it is s ++ in the bulk.…”

Section: Discussionmentioning

confidence: 70%

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Field-induced coexistence of s++ and s± superconducting states in dirty multiband superconductors

et al. 2018

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In multiband systems, such as iron-based superconductors, the superconducting states with locking and anti-locking of the interband phase differences, are usually considered as mutually exclusive. For example, a dirty two-band system with interband impurity scattering undergoes a sharp crossover between the s± state (which favors phase anti locking) and the s++ state (which favors phase locking). We discuss here that the situation can be much more complex in the presence of an external field or superconducting currents. In an external applied magnetic field, dirty two-band superconductors do not feature a sharp s± → s++ crossover but rather a washed-out crossover to a finite region in the parameter space where both s± and s++ states can coexist for example as a lattice or a microemulsion of inclusions of different states. The current-carrying regions such as the regions near vortex cores can exhibit an s± state while it is the s++ state that is favored in the bulk. This coexistence of both states can even be realized in the Meissner state at the domain's boundaries featuring Meissner currents. We demonstrate that there is a magnetic-field-driven crossover between the pure s± and the s++ states.

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Section: Discussionmentioning

confidence: 70%

“…This result has direct implications for local probes of superconducting states, such as the one proposed in Refs. [22][23][24], and for Josephson junction experiments. The coexistence state will manifest itself in the existence of signatures of both the s ± and s ++ states depending on the probe's position.…”

Section: Discussionmentioning

confidence: 99%

Field-induced coexistence of s++ and s± superconducting states in dirty multiband superconductors

et al. 2018

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“…3c for s ± and s ++ gaps, where sign of the gap was imposed by hand. The sign of ρ ÀTh s ± does not change for the energy values within the superconducting gap and its amplitude peaks at the energy E % Δ e1 Δ h1 , both characteristics of a sign changing gap 37 ; contrariwise ρ ÀTh sþþ changes sign indicative of same sign energy gaps throughout.…”

Section: Resultsmentioning

confidence: 93%

Multi-atom quasiparticle scattering interference for superconductor energy-gap symmetry determination

et al. 2021

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Complete theoretical understanding of the most complex superconductors requires a detailed knowledge of the symmetry of the superconducting energy-gap $${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$ Δ k α , for all momenta k on the Fermi surface of every band α. While there are a variety of techniques for determining $$|{\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha |$$ ∣ Δ k α ∣ , no general method existed to measure the signed values of $${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$ Δ k α . Recently, however, a technique based on phase-resolved visualization of superconducting quasiparticle interference (QPI) patterns, centered on a single non-magnetic impurity atom, was introduced. In principle, energy-resolved and phase-resolved Fourier analysis of these images identifies wavevectors connecting all k-space regions where $${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$ Δ k α has the same or opposite sign. But use of a single isolated impurity atom, from whose precise location the spatial phase of the scattering interference pattern must be measured, is technically difficult. Here we introduce a generalization of this approach for use with multiple impurity atoms, and demonstrate its validity by comparing the $${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$ Δ k α it generates to the $${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$ Δ k α determined from single-atom scattering in FeSe where s± energy-gap symmetry is established. Finally, to exemplify utility, we use the multi-atom technique on LiFeAs and find scattering interference between the hole-like and electron-like pockets as predicted for $${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$ Δ k α of opposite sign.

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“…In this respect, a promising alternative technique was recently proposed based on phase-sensitive quasiparticle interference (QPI) or Fourier transform scanning tunneling microscopy (FT-STM). Its application in LiOH-intercalated FeSe [22] and NaFe 1−x Co x As [23] has revealed qualitative differences in the integrated antisymmetrized intensities of the local density of states (LDOS) to determine the sign-reversal order parameter [24][25][26]. In this paper, we make theoretical predictions on the QPI with both intraband and interband impurity scatterings in CeCu 2 Si 2 .…”

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confidence: 99%

Revealing sign-reversal $s^{+-}$-wave pairing by quasiparticle interference in the heavy-fermion superconductor CeCu$_2$Si$_2$

Zhao,

Liu,

Yang

et al. 2021

Preprint

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Recent observations of two nodeless gaps in superconducting CeCu2Si2 have raised intensive debates as to its exact gap structure of either sign-reversal (s +− ) or sign-preserving (s ++ ) pairing.Here we investigate the quasiparticle interference (QPI) using realistic Fermi surface topology for both weak and strong interband impurity scatterings. Our calculations of the QPI and integrated antisymmetrized local density of states reveal qualitative distinctions between s +− and s ++ pairing states, which include the intragap impurity resonance and a significant energy-dependence difference between two gap energies. Our predictions provide a guide for phase-sensitive QPI measurements to uncover decisively the true pairing symmetry in the heavy-fermion superconductor CeCu2Si2.

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Detecting sign-changing superconducting gap in LiFeAs using quasiparticle interference

Cited by 15 publications

References 49 publications

Field-induced coexistence of s++ and s± superconducting states in dirty multiband superconductors

Field-induced coexistence of s++ and s± superconducting states in dirty multiband superconductors

Multi-atom quasiparticle scattering interference for superconductor energy-gap symmetry determination

Revealing sign-reversal $s^{+-}$-wave pairing by quasiparticle interference in the heavy-fermion superconductor CeCu$_2$Si$_2$

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