We report results of systematic de Haas-van Alphen (dHvA) studies on Ce 1−x Yb x CoIn 5 single crystals with varying Yb concentration. For x = 0.1, the well-known Fermi surfaces and the heavy effective masses of CeCoIn 5 (x = 0) have changed only slightly. We start to observe changes of the Fermi-surface topology at x = 0.2 leading to a drastic reconstruction above x = 0.55. At these concentrations, the effective masses are reduced considerably to values between 0.7 and 2.6 free electron masses. For both YbCoIn 5 and CeCoIn 5 , the angular-resolved dHvA frequencies can be very well described by conventional density-functional theory calculations. Projection of the Bloch states onto atomic Yb-4f orbitals yields a 4f occupation of 13.7 electrons, in agreement with previous experimental results indicating an intermediate Yb valence of +2.3.
The atomic structure of ultrathin iron films deposited on the (0001) surface of the topological insulator Bi2Se3 is analyzed by surface x-ray absorption spectroscopy. Iron atoms deposited on a Bi2Se3 (0001) surface kept at 160 K substitute bismuth atoms within the first quintuple layer. Iron atoms are neighbored by six selenium atoms at a distance in the 2.4Å range indicating substantial atomic relaxations. Mild annealing up to 520 K leads to the formation of α-FeSe, characterized by a local order extending up to the sixth shell (5.80Å). Ab-initio calculations predict a non-collinear magnetic ordering with a transition temperature of 3.5-10 K depending on the iron concentration and the number of the layers in which Fe is located.
Momentum resolved photoemission spectroscopy indicates the instability of the Dirac surface state upon deposition of gold on the (0001) surface of the topological insulator Bi2Se3. Based on the structure model derived from extended x-ray absorption fine structure experiments showing that gold atoms substitute bismuth atoms, first principles calculations provide evidence that a gap appears due to hybridization of the surface state with gold d-states near the Fermi level. Our findings provide new insights into the mechanisms affecting the stability of the surface state.PACS numbers: 61. 05.cp, 73.20.At, 71.15.Mb, Topological protection of the Dirac electrons at the three-dimensional topological insulator (TI) surface caused enormous interest in these materials as potential candidates for spintronics [1,2]. This remarkable property guarantees that the Dirac electrons of a TI surface do not experience the backscattering whatever the surface quality is. The only crucial condition to be met to secure that behavior is the absence of the time-reversal symmetry breaking perturbations, for instance, an out-of-plane ferromagnetism. Therefore, since the very discovery of the three-dimensional TIs, considerable experimental effort has been devoted to the confirmation of the topological protection. The most striking evidences of the property include the absence of the elastic backscattering on the disordered or defected surfaces [3][4][5][6], existence of the well-defined Dirac states at the thallium-based 3D TI's surfaces exhibiting complex morphology [7,8], and the tolerance of the topological states to the in-plane [9,10] or, possibly, non-collinear [11] magnetic moments.
We report on a comprehensive de Haas-van Alphen (dHvA) study of the iron pnictide LaFe 2 P 2 . Our extensive density-functional band-structure calculations can well explain the measured angular-dependent dHvA frequencies. As salient feature, we observe only one quasi-two-dimensional Fermi-surface sheet; i.e., a hole-like Fermi-surface cylinder around , essential for s ± pairing, is missing. In spite of considerable mass enhancements due to many-body effects, LaFe 2 P 2 shows no superconductivity. This is likely caused by the absence of any nesting between electron and hole bands.
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