Irreversible proliferation of magnetic moments at cleaved surfaces of the topological Kondo insulator SmB6

The compound SmB$_6$ is the best established realization of a topological Kondo insulator, in which a topological insulator state is obtained through Kondo coherence. Recent studies have found evidence that the surface of SmB$_6$ hosts ferromagnetic domains, creating an intrinsic platform for unidirectional ballistic transport at the domain boundaries. Here, surface-sensitive X-ray absorption (XAS) and bulk-sensitive resonant inelastic X-ray scattering (RIXS) spectra are measured at the Sm N$_{4,5}$-edge, and used to evaluate electronic symmetries, excitations and temperature dependence near the surface of cleaved samples. The XAS data show that the density of large-moment atomic multiplet states on a cleaved surface grows irreversibly over time, to a degree that likely exceeds a related change that has recently been observed in the surface 4f orbital occupation

Spectromicroscopic measurement of surface and bulk band structure interplay in a disordered topological insulator

Topological insulators are bulk semiconductors that manifest in-gap massless Dirac surface states due to the topological bulk-boundary correspondence principle [1-3]. These surface states have been a subject of tremendous ongoing interest, due both to their intrinsic properties and to higher order emergence phenomena that can be achieved by manipulating the interface environment [4-11]. Here, angle resolved photoemission (ARPES) spectromicroscopy and supplementary scanning tunneling microscopy (STM) are performed on the model topological insulator Bi2Se3 to investigate the interplay of crystallographic inhomogeneity with the topologically ordered bulk and surface band structure. Quantitative analysis methods are developed to obtain key spectroscopic information in spite of a limited dwell time on each measured point. Band energies are found to vary on the scale of 50 meV across the sample surface, enabling single-sample measurements that are analogous to a multi-sample doping series (termed a "binning series"). Focusing separately on the surface and bulk electrons reveals a nontrivial hybridization-like interplay between fluctuations in the surface and bulk state energetics.Comment: 4 figures and 6 supplementary figure

Observation of a topological insulator Dirac cone reshaped by non-magnetic impurity resonance

The massless Dirac electrons found at topological insulator surfaces are thought to be influenced very little by weak, non-magnetic disorder. However, a resonance effect of strongly perturbing non-magnetic impurities has been theoretically predicted to change the dispersion and physical nature of low-energy quasiparticles, resulting in unique particle-like states that lack microscopic translational symmetry. Here we report the direct observation of impurities reshaping the surface Dirac cone of the model three-dimensional topological insulator bismuth selenide. A pronounced kink-like dispersion feature is observed in disorder-enriched samples, and found to be closely associated with the anomaly caused by impurity resonance in the surface state density of states, as observed by dichroic angle-resolved photoemission spectroscopy. The experimental observation of these features, which closely resemble theoretical predictions, has significant implications for the properties of topological Dirac cones in applied scenarios that commonly feature point-defect disorder at surfaces or interfaces. Topological insulators - influence of surface impurities: The electronic properties of topological insulators are robust against perturbations, including the presence of non-magnetic impurities. However, surface impurities can give rise to resonant states near the Dirac point, and if their density becomes sufficiently high it is predicted that they can substantially modify the dispersion of the Dirac cone and develop a collective behaviour that results in the formation of particle-like states that lack microscopic translational symmetry. L. Andrew Wray at Purdue University and at the New York University Shanghai, and colleagues, used angle-resolved photoemission spectroscopy to experimentally observe the reshaping of the surface Dirac cone in a defect-rich sample of the topological insulator Bi2Se3. These results indicate that surface impurities can provide a useful handle to control the properties of topological insulators

COLECCIÓN LUIS SUÁREZ GALVÁN [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201