European XFEL Science Seminar | k-resolved electronic structure by soft-X-ray ARPES: From 3D materials to heterostructures and impurities

by Dr. Vladimir Strocov (Paul Scherrer Insitute, Swiss Light Source)

Tuesday, March 21, 2017 from to (Europe/Berlin)
at European XFEL ( E1.173 (Schenefeld) )
	ARPES is the unique tool to explore electronic structure of various solid-state systems resolved in electron momentum k. Pushing this technique into the soft-X-ray energy range (SX-ARPES) brings virtues of enhanced photoelectron escape depth and a possibility of resonant photoexcitation delivering elemental and chemical state specificity [1]. In this talk I unfold recent applications of SX-ARPES to 3D crystalline systems, buried interfaces and impurity systems.
	3D materials. These applications utilize sharp definition of surface-perpendicular momentum resulting from the enhanced photoelectron delocalization. An example is the perovskite La1 xSrxMnO3 where "shadow" contours of the experimental Fermi surface reveal the rhombohedral lattice distortion affecting the CMR [2]. Other examples include polarons in Ce-doped CaMnO3, charge-density waves in VSe2 originating from its 3D nested Fermi surface, Weil semimetals, etc.
	Buried heterostructures. Our example is the LaAlO3/SrTiO3 interface embedding mobile 2D electron gas. Resonant SX-ARPES at the interface Ti3+ ions resolves band structure of the interface quantum well states, with their peak-dip-hump spectral function manifesting polaronic nature of the interface charge carriers fundamentally limiting their mobility [3]. Pump-probe XFEL experiments on polaronic systems will allow separation of the e-e and e-ph interaction effects having different time scales. Further examples include multiferroic BaTiO3/La1-xSrxMnO3 interfaces, EuO/Si spin injectors, GaN-based transistor structures and other buried systems in the heart of nowadays device physics.
	Buried impurities. Resonant SX-ARPES applied to the paradigm diluted magnetic semiconductor GaMnAs identifies the ferromagnetic Mn impurity band and establishes the mechanism of its hybridization with the host GaAs bands determining the transport properties [4]. Other examples include InFeAs with a different mechanism of ferromagnetic electron transport, magnetic Mn impurities opening the Zeeman gap in the ferroelectric Rashba semiconductor GeTe [5], etc.

[1] V.N. Strocov et al, Synchr. Rad. News 27, N2 (2014) 31
[2] L.L. Lev et al, Phys. Rev. Lett. 114 (2015)
[3] C. Cancellieri et al, Nature Comm. 7 (2016) 10386
[4] M. Kobayashi et al, Phys. Rev. B 89 (2014) 205204
[5] J. Krempaský et al, Nature Comm. 7 (2016) 13071

Host: Serguei Molodtsov