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The symmetry of a surface or interface plays an important role in determining the spin splitting and texture of a two-dimensional band. Spin-polarized bands of a triangular lattice atomic layer (TLAL) consisting of Sn on a SiC(0001) substrate is investigated by spin- and angle-resolved photoelectron spectroscopy. Surprisingly, both Zeeman- and Rashba-type spin-split bands, without and with spin degeneracy, respectively, coexist at a K point of the Sn TLAL. The K point has a threefold symmetry without inversion symmetry according to the crystal structure including the SiC periodicity, meaning that the Zeeman-type is consistent with the symmetry of the lattice while the Rashba-type is inconsistent. Our density functional calculations reveal that the charge density distribution of the Rashba-type (Zeeman-type) band shows (no) inversion symmetry at the K point. Therefore, the symmetry of the charge density distribution agrees with both types of the spin splitting. [ABSTRACT FROM AUTHOR]

We report an angle-resolved photoemission (ARPES) study of β - YbAlB4, which is known to harbor unconventional quantum criticality (QC) without any tuning. We directly observe a quasiparticle peak (QP) emerging from hybridization, characterized by a binding energy and an onset of coherence both at about 4 meV. This value conforms with a previously observed reduced Kondo scale at about 40 K. Consistency with an earlier study of carriers in β - YbAlB4 via the Hall effect strongly suggests that this QP is responsible for the QC in β - YbAlB4 . A comparison with the sister polymorph α; - YbAlB4, which is not quantum critical at ambient pressure, further supports this result. Indeed, within the limitation of our instrumental resolution, our ARPES measurements do not show tangible sign of hybridization in this locally isomorphic system, while the conduction band we observe is essentially the same as in β - YbAlB4. We therefore claim that we identified by ARPES the carriers responsible for the QC in β - YbAlB4. The observed dispersion and the underlying hybridization of this QP are discussed in the context of existing theoretical models. [ABSTRACT FROM AUTHOR]

Using a laser-excited angle-resolved photoemission spectroscopy capable of bulk sensitive and high-energy resolution measurements, we reveal a new phenomenon of superconductors in the optimally doped trilayer Bi2Sr2Ca2Cu3O10+δ. We observe a hybridization of the Bogoliubov bands derived from the inner and outer CuO2 planes with different magnitudes of energy gaps. Our data clearly exhibit the splitting of coherent peaks and the consequent enhancement of spectral gaps. These features are reproduced by model calculations, which indicate that the gap enhancement extends over a wide range of Fermi surface up to the antinode. The significant modulation of electron pairing uncovered here might be a crucial factor to achieve the highest critical temperature in the trilayer cuprates. [ABSTRACT FROM AUTHOR]