k-resolved electronic structure by soft-X-ray ARPES: From 3D systems to buried interfaces and impurities

DIPC Seminars

V. Strocov (Swiss Light Source and Paul Scherrer Institute)
Donostia International Physics Center
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k-resolved electronic structure by soft-X-ray ARPES: From 3D systems to buried interfaces and impurities k-resolved electronic structure by soft-X-ray ARPES: From 3D systems to buried interfaces and impurities Vladimir N. STROCOV Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen-PSI, Switzerland ABSTRACT: ARPES is the unique tool to explore electronic structure of solid-state systems resolved in electron momentum k. Pushing this technique into the soft-X-ray energy range (SX-ARPES) extends its applications from surface physics towards 3D crystal systems, buried interfaces and impurity systems. These spectroscopic abilities result from enhancement of the photoelectron escape depth and a possibility of resonant photoexcitation delivering the elemental and chemical state specificity. In this talk, I unfold a diversity of new scientific highlights achieved with SX-ARPES [1]. 3D materials. The applications to 3D systems are based on sharp definition of surface-perpendicular momentum k resulting from the enhanced photoelectron delocalization. An example is the 3D perovskite La(1-x)Sr(x)MnO3 exhibiting CMR properties due to interplay of the double-exchange itineracy and polaronic self-localization. The experimental 3D Fermi surface (FS) reveals characteristic "shadow" contours, resembling those in cuprates, which manifest the rhombohedral structural distortion reducing the CMR critical temperature. Other applications include VSe2 with charge-density waves resulting from 3D nesting of its FS, bulk Rashba splitting in non-centrosymmetric topological insulator BiTeI, conventional superconductor MgB2, Fermi states in quasicrystalline AlNiCo, etc. Buried heterostructures. The LaAlO3/SrTiO3 interface of two transition metal oxides embeds mobile 2D electron gas. Its signal can be accentuated using resonant SX-ARPES at the interface Ti3+ ions, which exposes the dxy-, dyz- and dxz- derived subbands localized in the interface quantum well. Their intensity variations in k-space reveal the Fourier composition of their wavefunctions. The peak-dip- hump spectral function manifests strong polaronic coupling of interface electrons as the fundamental limit of their temperature-dependent mobility. Oxygen vacancies increase the electron concentration, as expressed by the Luttinger count of the FS, and reduce the polaronic coupling. These findings extend to other oxide heterostructure systems. Buried impurities. Resonant SX-ARPES applied to the paradigm diluted magnetic semiconductor GaMnAs has identified the ferromagnetic Mn impurity band, and established its energy alignment and mechanism of hybridization with the host GaAs bands. Combining the previous p-d exchange and double-exchange models, these results suggest a microscopic picture of the GaMnAs ferromagnetism based on the Anderson impurity model. Another example is InFeAs showing the ferromagnetism induced by doped highly mobile electron carriers. [1] V.N. Strocov et al, Synchr. Rad. News 27, N2 (2014) 31