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Competing electronic states emerging on polar surfaces

ABSTRACT: Excess charge on polar surfaces of ionic compounds is commonly described by the two-dimensional electron gas (2DEG) model, a homogeneous distribution of charge, spatially-confined in a few atomic layers. Here, by combining scanning probe microscopy with density functional theory calculations, we show that excess charge on the polar TaO2 termination of KTaO3(001) forms more complex electronic states with different degrees of spatial and electronic localization: charge density waves (CDW) coexist with strongly-localized electron polarons and bipolarons. These surface electronic reconstructions, originating from the combined action of electron-lattice interaction and electronic correlation, are energetically more favorable than the 2DEG solution. They exhibit distinct spectroscopy signals and impact on the surface properties, as manifested by a local suppression of ferroelectric distortions. Defect-free surfaces with excess charge are typically described as a homogeneous 2D electron gas. Here, in contrast, the authors find that the KTaO3(001) surface hosts a charge density wave coexisting with a pattern of electron polarons, highly localized states of excess electrons bound to a lattice distortion.

SUBMITTER: Reticcioli M

PROVIDER: S-EPMC9314351 | biostudies-literature | 2022 Jan

REPOSITORIES: biostudies-literature

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