Volatile two-dimensional electron gas in ultrathin BaTiO3 films

Sara Fatale, Marco Grioni, Luca Moreschini, Simon Karl Moser
AMER PHYSICAL SOC, 2018
Article

We investigate the metallic surface state in ultrathin films of BaTiO3 by angle-resolved photoemission spectroscopy. We find Fermi-surface contours derived from the Ti 3d t(2g) conduction band, similar as in SrTiO3 but with broader spectral features due to enhanced quasiparticle scattering. Oxygen vacancies created in the x-ray beam spot allow for reversible in situ doping control up to surface carrier densities as high as 1014 cm(-2), but vacancy migration into the subsurface at T >= 285 K quenches the surface state. Our analysis suggests that the charge state of oxygen vacancies in ultrathin films is predominantly 2+, which limits charge-carrier trapping and the formation of localized defect states.

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Sara Fatale, Marco Grioni, Luca Moreschini, Simon Karl Moser
AMER PHYSICAL SOC, 2018
Article

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https://infoscience.epfl.ch/record/262114?ln=fr

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vignette|Dispositif expérimental de spectroscopie photoélectronique résolue en angle|alt=|300x300px La spectroscopie photoélectronique résolue en angle (ARPES), est une technique expérimentale direct

La spectroscopie photoélectronique (photoelectron spectroscopy, PES) ou spectroscopie de photoémission (photoemission spectroscopy) est un ensemble de méthodes spectroscopiques basées sur la détect

La densité de charge électrique désigne la quantité de charge électrique par unité d'espace. Selon que l'on considère un problème à 1, 2 ou 3 dimensions, c'est-à-dire une ligne, une surface ou un vol

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Bulk and surface Rashba splitting in single termination BiTeCl

Jan Hugo Dil, Stefan Peter Muff, Thorsten Schmitt, Vladimir N. Strocov

By angle-resolved photoemission spectroscopy (ARPES) we observe a giant Rashba-type spin splitting in the electronic bulk conduction and valence bands of the semiconductor BiTeCl. This material belongs to the group of bismuth tellurohalides BiTeX (X=Cl,Br,I) which are layered non-centrosymmetric materials with strong spin-orbit interaction. By photon energy-dependent ARPES, we separate the bulk and surface contribution of the electronic structure and show that the tellurium-terminated (0001) crystal surface hosts spin-split two-dimensional surface states. On the chlorine-terminated surface at the opposite side of the crystal no surface states are observed due to photon-induced surface chemistry.

2013

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Insight into the electronic structure of semiconducting epsilon-GaSe and epsilon-InSe

Helmuth Berger, Alberto Crepaldi, Marco Grioni, Daniela Pacilè

Metal monochalcogenides (MX) have recently been rediscovered as two-dimensional materials with electronic properties highly dependent on the number of layers. Although some intriguing properties appear in the few-layer regime, the carrier mobility of MX compounds increases with the number of layers, motivating the interest in multilayered heterostructures or bulk materials. By means of angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory calculations, we compare the electronic band structure of bulk epsilon-GaSe and epsilon-InSe semiconductors. We focus our attention on the top valence band of the two compounds along main symmetry directions, discussing the effect of spin-orbit coupling and contributions from post-transition-metal (Ga or In) and Se atoms. Our results show that the top valence band at Gamma point is dominated by Se p(z) states, while the main effect of Ga or In appears more deeply in binding energy, at the Brillouin zone corners, and in the conduction band. These findings explain also the experimental observation of a hole effective mass rather insensitive to the post-transition metal. Finally, by means of spin-resolved ARPES and surface band structure calculations we describe Rashba-Bychkov spin splitting of surface states in epsilon-InSe.

AMER PHYSICAL SOC2020

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