Abstract
Quasicrystals (QCs) are intermetallic alloys that have excellent long-range order but lack translational symmetry in at least one dimension. The valence band electronic structure near the Fermi energy EF in such materials is of special interest since it has a direct relation to their unusual physical properties. However, the Fermi surface (FS) topology as well as the mechanism of QC structure stabilization are still under debate. Here we report the first observation of the three-dimensional FS and valence band dispersions near EF in decagonal Al70Ni20Co10 (d-AlNiCo) QCs using soft X-ray angle-resolved photoemission spectroscopy. We show that the FS, formed by dispersive Al sp-states, has a multicomponent character due to a large contribution from high-order bands. Moreover, we discover that the magnitude of the gap at the FS related to the interaction with Brillouin zone boundary (Hume–Rothery gap) critically differs for the periodic and quasiperiodic directions.
Highlights
Quasicrystals (QCs) are intermetallic alloys that have excellent long-range order but lack translational symmetry in at least one dimension
In Angleresolved photoemission spectroscopy (ARPES), the HR gap should be clearly observed as bending of the band dispersions closer to EF32 at the q-Brillouin zone (q-BZ) boundary, which leads to the formation of a pseudogap at EF
Increase of the photoelectron mean free path l at higher photoelectron energies make the SX-ARPES experiment more bulk sensitive[33], which is essential for the QC samples because their surface stoichiometry may be distorted by structural defects and surface segregation
Summary
Quasicrystals (QCs) are intermetallic alloys that have excellent long-range order but lack translational symmetry in at least one dimension. The very existence of the decagonal QCs poses fundamental questions on how the duality between the periodic and QP orders manifests itself in electronic structure and how it is related to the stabilization of their unusual structure These questions have been explored in a number of theoretical articles[4,5,6,7,8,9,10,11] and experimental works[12,13,14,15,16,17,18,19]. The real FS could be obtained by increasing the set of G-vectors and taking into account the structure factors as well as all possible Bragg scattering effects at the q-BZ boundaries The latter open multiple gaps at the EF at certain points in k-space and transform the FS into a segmented FS that has a smaller surface area compared with the original one. Theoretical FSs were calculated ab initio for Y-AlNiCo structural model[6] and for orthorhombic approximant to the decagonal phase[10], both resulting in a highly anisotropic FS with a complex multipleband structure
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