5 research outputs found
Severe dirac mass gap suppression in Sb 2 Te 3-based quantum anomalous Hall materials
The quantum anomalous Hall (QAH) effect appears in ferromagnetic topological insulators (FMTIs) when a Dirac mass gap opens in the spectrum of the topological surface states (SSs). Unaccountably, although the mean mass gap can exceed 28 meV (or ∼320 K), the QAH effect is frequently only detectable at temperatures below 1 K. Using atomic-resolution Landau level spectroscopic imaging, we compare the electronic structure of the archetypal FMTI Cr0.08(Bi0.1Sb0.9)1.92Te3 to that of its nonmagnetic parent (Bi0.1Sb0.9)2Te3, to explore the cause. In (Bi0.1Sb0.9)2Te3, we find spatially random variations of the Dirac energy. Statistically equivalent Dirac energy variations are detected in Cr0.08(Bi0.1Sb0.9)1.92Te3 with concurrent but uncorrelated Dirac mass gap disorder. These two classes of SS electronic disorder conspire to drastically suppress the minimum mass gap to below 100 μeV for nanoscale regions separated by <1 μm. This fundamentally limits the fully quantized anomalous Hall effect in Sb2Te3-based FMTI materials to very low temperatures
Orbital selective pairing and gap structures of iron-based superconductors
We discuss the influence on spin-fluctuation pairing theory of orbital
selective strong correlation effects in Fe-based superconductors, particularly
Fe chalcogenide systems. We propose that a key ingredient for an improved
itinerant pairing theory is orbital selectivity, i.e., incorporating the
reduced coherence of quasiparticles occupying specific orbital states. This
modifies the usual spin-fluctuation via suppression of pair scattering
processes involving those less coherent states and results in orbital selective
Cooper pairing of electrons in the remaining states. We show that this paradigm
yields remarkably good agreement with the experimentally observed anisotropic
gap structures in both bulk and monolayer FeSe, as well as LiFeAs, indicating
that orbital selective Cooper pairing plays a key role in the more strongly
correlated iron-based superconductors.Comment: 13 pages, 10 figures, published versio