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Effective models focused on pertinent low-energy degrees of freedom have substantially contributed to our qualitative understanding of quantum materials. An iconic example, the Kondo model, was key to demonstrating that the rich phase diagrams of correlated metals originate from the interplay of localized and itinerant electrons. Modern electronic structure calculations suggest that to achieve quantitative material-specific models, accurate consideration of the crystal field and spin-orbit interactions is imperative. This poses the question of how local high-energy degrees of freedom become incorporated into a collective electronic state. Here, we use resonant inelastic x-ray scattering (RIXS) on CePd3 to clarify the fate of all relevant energy scales. We find that even spin-orbit excited states acquire pronounced momentum-dependence at low temperature—the telltale sign of hybridization with the underlying metallic state. Our results demonstrate how localized electronic degrees of freedom endow correlated metals with new properties, which is critical for a microscopic understanding of superconducting, electronic nematic, and topological states. The fate of high-energy degrees of freedom, such as spin-orbit interactions, in the coherent state of Kondo lattice materials remains unclear. Here, the authors use resonant inelastic x-ray scattering in CePd3 to show how Kondo-quasiparticle excitations are renormalized and develop a pronounced momentum dependence, while maintaining a largely unchanged spin-orbit gap. [ABSTRACT FROM AUTHOR]

The present article highlights two aspects at the intersection between Rashba physics and topological matter. Topologically nontrivial matter has been in the focus for almost two decades. It depends strongly on spin–orbit coupling but, in contrast to large parts of modern solid state physics, strong electron correlation does not play a major role. In this context, SmB6 has been suggested as the first topological insulator driven by strong electron correlation and the first topological Kondo insulator. We review the important role of the Rashba splitting in determining that the observed surface states are not topological. Moreover, we point out that the Rashba splitting of SmB6 represents the extreme case of a large splitting in momentum space at a small Rashba parameter. [ABSTRACT FROM AUTHOR]

Magnetically doped topological insulators enable the quantum anomalous Hall effect (QAHE), which provides quantized edge states for lossless charge-transport applications1–8. The edge states are hosted by a magnetic energy gap at the Dirac point2, but hitherto all attempts to observe this gap directly have been unsuccessful. Observing the gap is considered to be essential to overcoming the limitations of the QAHE, which so far occurs only at temperatures that are one to two orders of magnitude below the ferromagnetic Curie temperature, TC (ref. 8). Here we use low-temperature photoelectron spectroscopy to unambiguously reveal the magnetic gap of Mn-doped Bi2Te3, which displays ferromagnetic out-of-plane spin texture and opens up only below TC. Surprisingly, our analysis reveals large gap sizes at 1 kelvin of up to 90 millielectronvolts, which is five times larger than theoretically predicted9. Using multiscale analysis we show that this enhancement is due to a remarkable structure modification induced by Mn doping: instead of a disordered impurity system, a self-organized alternating sequence of MnBi2Te4 septuple and Bi2Te3 quintuple layers is formed. This enhances the wavefunction overlap and size of the magnetic gap10. Mn-doped Bi2Se3 (ref. 11) and Mn-doped Sb2Te3 form similar heterostructures, but for Bi2Se3 only a nonmagnetic gap is formed and the magnetization is in the surface plane. This is explained by the smaller spin–orbit interaction by comparison with Mn-doped Bi2Te3. Our findings provide insights that will be crucial in pushing lossless transport in topological insulators towards room-temperature applications. In theory, the anomalous quantum Hall effect is observed in edge channels of topological insulators when there is a magnetic energy gap at the Dirac point; this gap has now been observed by low-temperature photoelectron spectroscopy in Mn-doped Bi2Te3. [ABSTRACT FROM AUTHOR]

SmB6 is predicted to be the first member of the intersection of topological insulators and Kondo insulators, strongly correlated materials in which the Fermi level lies in the gap of a many-body resonance that forms by hybridization between localized and itinerant states. While robust, surface-only conductivity at low temperature and the observation of surface states at the expected high symmetry points appear to confirm this prediction, we find both surface states at the (100) surface to be topologically trivial. We find the Γ̅ state to appear Rashba split and explain the prominent X̅ state by a surface shift of the many-body resonance. We propose that the latter mechanism, which applies to several crystal terminations, can explain the unusual surface conductivity. While additional, as yet unobserved topological surface states cannot be excluded, our results show that a firm connection between the two material classes is still outstanding. [ABSTRACT FROM AUTHOR]

The present article highlights two aspects at the intersection between Rashba physics and topological matter. Topologically nontrivial matter has been in the focus for almost two decades. It depends strongly on spin–orbit coupling but, in contrast to large parts of modern solid state physics, strong electron correlation does not play a major role. In this context, SmB6 has been suggested as the first topological insulator driven by strong electron correlation and the first topological Kondo insulator. We review the important role of the Rashba splitting in determining that the observed surface states are not topological. Moreover, we point out that the Rashba splitting of SmB6 represents the extreme case of a large splitting in momentum space at a small Rashba parameter. [ABSTRACT FROM AUTHOR]